Applications of surface acoustic and shallow bulk acoustic ...ieee-uffc.org/wp-content/uploads/2016/09/e89a1453.pdf · Extensive development of shallow bulk acoustic wave (SBAW) devices

Applications of Surface Acoustic and Shallow Bulk Acoustic Wave Devices COLIN K CAMPBELL FELLOW I EEE

Invited Paper

Applications of surface acoustic wave (SA W) and shallow bulk acoustic wave (SBA W) devices are reviewed SA W-device coverage includes delay lines and filters operating at selected frequencies in the ra nge from about 10 MHz to 11 GHz modeling with singleshycrystal piezoelectrics and layered structures resonators and lowshyloss filters comb filters and multiplexers antenna duplexers harshymonic devices chirp filters for pulse compression coding with fixed and programmable transversal filters Barker and quadrashyphase coding adaptive filters acoustic and acoustoelectric conshyvolvers and correia tors for radar spread spectrum and packet radio acoustooptic processors for Bragg modulation and spectrum analshyysis real-time Fourier-transform and cepstrum processors for radar and sonar compressive receivers Nyquist filters for microwave digita l radio clock-recovery filters for optical fiber communicashytions fixed- tunable- and multimode-oscillators and frequency synthesizers acoustic charge transport (ACT) and other SA W devices for signal processing on gallium arsenide SA W sensors and scanning acoustic microscopy

SBA W-devices applications include gigahertz delay lines surshyface transverse wave resonators employing energy-trapping gratshyings as well as oscillators with enhanced performance and capashybility

I INTRODUCTION

A SA W-Device Development

The phenomenon of s u rface acoustic wave (SAW) propshyagation was f i rst repo rted on by Lord Rayleigh in 1885 [1] It was not until 1965 however that such wave motion (also known as Rayleigh waves) was efficiently uti l ized fo r elecshytronic fi lter and analog si gnal-processing appl ications by the use of vol tage-excited metal-fi l m interdigital transshydu cers ( l DTs) on the su rface of a piezoelectric su bstrate [2]

Fol lowing th is development consu mer electronic intershyests in SAW devices init ia l ly focused on the l arge-volu me low-cost market for intermediate freq uency (IF) f i l ters fo r dom estic TV receivers Mi l itary and co mme rcial developshyments related to low-volu me h igh-cost SAW chi rp fi lters for radar s ignal processing This rapidly expanded into a

Manuscript received December 9 1988 revised April 27 1989 This work was supported in part by the National Sciences amp Engishyneering Research Council of Canada

The author is with the Department of Electrical and Computer Engineering McMaster University Hamilton Ontario L8S 4L7 Canada

IEEE Log Number 8929588

multitude of p rod ucts and appl ications however in exploiting the capabi l it ies of SAW devices Mechanical attr i butes cont r ibuting to t h i s expansion are ruggedness l ig ht weight and smal l size Electrical merits featu re the abi l ity for s ignal process ing at selected f req u enc ies in the range from about 10 MHz up to a c u rrent repo rted val ue of 11 GHz [3]

Whi le their c i rc u it use was init ia l ly l i m ited to i m plemenshytation in intermediate frequency ( I F) stages with large s i gshynal-voltage levels as d ictated by the high va lues of insertion loss ( 1 5-40 dB) inherent in fi rst generation SAW devices much research has been su bseq uently appl ied to SAW fi lters with insertion loss less than 3 dB for low sigshynal-level or receiver front-end fi ltering For example SAW fi lters with 3-5-W power-hand l ing capabi l it ies are employed in antenna d u plexers fo r mobi le telephone transceivers operating at 835 MHz [4] Al so increasing th rust has been appl ied to SAW-based s ignal p rocess ing and integrated-c i rshycuit com pati b i l ity on gal l i u m arsenide (GaAs) which is a piezoelectric as wel l as a sem icond ucto r

Overal l the demand for SAW devices has led to a comshymercial mar ket currently running at a multi-m i l l ion level in both annual dol lar sales and device quantity Tosh iba in Japan now produces about 5 m i l l ion SAW devices per month mainly fo r IF filters and resonators fo r TV and VCR c i rcu its [5] To i l l u strate th is rapid growth Wi l l iam son [6] in 1977 reported 45 d i fferent types of SAW devices under development includ ing 1 0 major devices with widesp read appl ication In 1985 Hartmann [7] su bsequently l i sted nine major commercial appl ications nine major consumer appl ications and 1 8 major m i l itary appl ications of SAW technology Hi ghl ights of SAW-based device appl ications are given in Table 1

Extensive development of shal low b u l k acou stic wave (SBAW) devices has also been under way since about 1 977 These can have su perior perfo rmance to SAW cou nterparts in some appl ications SBAW devices involve s ignal proshycessing of acoustic bu lk waves that are constrained to propshyagate close to the piezoelectr ic subst rate su rface As l i sted in Table 2 SSBW resonators offer s u per ior performance in some stable osc i l lators req u i ring h igher power levels and or reduced sensitivity to su rface contamination and defects

0018-9219891000-1453$0100 (C) 1989 IEEE

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Table 1 Representative Applications of SAW Devices

Device Applications

Medium loss SAW filter IF filtering Clock recovery (nondispersive) Nyquist filters MSK

modulation SAW delay line Path length equalizers Altimeters

Pressure and temperature sensors Tunable oscillators Recirculating storage

Fixed-tap delay line Pulse compression radar Barker and quadraphase coding Radar return simulation

Programmable Adaptive filtering for spread transversal filter spectrum Matched filtering

Channel equalization Radar simulator

SAW Comb filter Multiplexers Multimode oscillators Counters

Low-loss SAW filter VHFUHF front-end filtering Mobile and cellular radio Antenna duplexer

SAW resonator Precision filters and fixed oscillators

SAW chirp filter Pulse compression radar Variable delay lines and multi path cancellation Real-time Fouriershytransform processors Wideshyband linear-phase filters Reflective array compressor with large TB product

Three- and four-port Matched filtering in spread SAW convolver spectrum Long-code

correlation Radar Packet radio Acoustic charge High-speed sampling Wide-band

transport on GaAs pn-code correlator Programmable filtering

Other SAW devices on Tunable delay lines and GaAs resonators Programmable

filters and correlators SAW-based Bragg modulators Spectrum

optoelectronic analyzers Wide-band devices convolvers and correlators

Monolithic integration on GaAs

Multilayered SAW Rugged resonators and filters devices Monolithic SAW convolvers and

correlators Sensors

Table 2 Some Current Applications of SBAW Devices

SBAW Type Applications

SSBW devices Mid-loss filtering with reduced sensitivity to surface contamination Operating frequencies up to about 60-percent higher than SAW-based counterparts

STW devices Low-loss filters Resonators with highershypower capability than SAW Stable oscillators

Moreover SBAW filters can be configured with center freshyquencies up to about 60-percent higher than with SAW devices using the same piezoelectric substrates and transshyducer geometries

Many features of SAW-device technology can be readily transferred to SBAW implementation since they involve the same microelectronic fabrication and production proshycesses and may use the same piezoelectric materials Some SBAW devices can be visually indistinguishable from their SAW counterparts differing only in the piezoelectric crysshytal orientations employed

Mechanical wave propagation in SBAW devices is often referred to as surface skimming bulk waves (SSBWs) when only input and output IDTstructures are involved In SBAW resonators incorporating energy-trapping gratings the wave motion is usually termed a surface transverse wave (STW) one Table 2 lists signal-processing applications of both of these SBAW-device types

B Aim of this Paper

In this paper the salient features of significant SAW and SSBW devices are reviewed in terms of their device paramshyeters and performance It is assumed that the reader has some knowledge of SAW device principles For the SAWshydevice review emphasis is given to developments over the past 10 years I nterested readers seeking more background material are referred to a n umber of textbooks deal ing with various aspects and treatments of this su bject [8]-[20] Early key papers on SAW devices are to be found in [21]-[23] Also other review papers deal with SAW filters [24] components for electronic warfare receivers [25] SAW-device applicashytions [26]-[29] SAW resonators [30]-[32] SAW materials [33] SAW waveguides [34] SAW waves and acoustoelectric interactions [35] [36] SAW reflective array structures [37] acoustooptic Bragg modulators for integrated optic comshymunications [38] SAW-based fixed and adaptive filtering on GaAs [39] hybrid programmable transversal filters [40] and SAW-based acoustic charge transport (ACT) processes and structures on GaAs [41] Principles of SBAW propagation and devices are contained in [42] and [43] A sensor classhysification scheme is presented in [44] The use of SAW conshyvolvers in spread-spectrum communications is reviewed in [45]-[47] with wide-band packet radio emphasized in [48] Specifics of SAW Fourier transform processors for intershyference rejection in spread-spectrum communications adaptive filtering real-time spectrum and cepstrum analshyysis for radar and sonar are in [19] [49] and [50] SAW and SBAW propagation in gallium arsenide are examined in [51] and [52]

Open-literature publications on SAW and SBAW devices are largely documented in a) IEEE TRANSACTIONS ON ULTRAmiddot

SONICS FERROELECTRONICS AND FREQUENCY CONTROL and its precedessor IEEE TRANSACTIONS ON SONICSAND ULTRASONICS

b) annualEEE Ultrasonics Symposium Proceedings c) PROshy

CE EDINGS OF THE IEEE and d) Proceedings of the Annual Freshyquency Control Symposium In view of the mass of literashyture on these subjects to date references in this paper mainly relate to the first three sources

II SAW CRYSTALS AND LAYERED STRUCTURES

A Representative SA W-Filter Specifications

Key parameters for nondispersive SAW bandpass filters with typical commercial specifications are shown in Table 3 The choice of piezoelectric substrate is basic to attainshyment of such specifications involving tradeoffs between insertion loss filter fractional bandwidth temperature stashybility and shape factor (SF) where SF = tfrll1 f such that I1f = bandwidth at 1-dB points I1f = ultimate rejection bandwidth (and SF = 1 is ideal) Figu re 1 shows the response of a precision commercial SAW filter for 70-MHz IF opershyation

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Table 3 Typical Commercial Specifications for Nondispersive SAW Filters

F i lter Parameter Specifications

Center frequency 10 MHz to 2 GHz I nsertion loss lt3 dB to gt30 dB Fractional bandwidth H 1 dB 006 to 40 Transition bandwidth 035 MHz to 2 MHz Shape Factor lt 11 to gt15 Passband Amplitude ripple plusmn03 dB Peak phase deviation plusmn 3deg Close-in sidelobe level 30 dB to 60 dB

CHi 521 log MAG 10 dBI REF -2779 dB

Avg16

Fig 1 Frequency response of a precision SAW fi lter with 70-dB out-of-band rejection Horizontal scale 40-100 MHz vertical scale 10 dBdiv (Courtesy of Crystal Technology Inc Palo Alto CA)

B Single-Crys tal Substrates for SA W DTs

Figu re 2(a) shows an elementary SAW fi lter em ploying inp ut and output i nterd igital transducers ( l OTs) on a s i ngleshycrystal piezoelectric substrate whi le F ig 2(b) gives an equ ivalent c i rc u it for eac h l OT i n terms of rad iation conshyductance Ga rad iation s u sceptance Ba and transducer capacitance Ct The fi lter f req uency response i s dictated by the electrode geometry of the voltage-excited i n put and output l OTs for lau nch ing and detect ing the SAW motion I n sertion loss ( I L) depends on the degree of match between l OT impedances and loadsou rce cou nterparts

S i ng le-crystal V-cut Z-propagat ing ( Y-Z) l ith ium n iobate

InputIDT

Piezoelectric substrate

(a)

(b) Fig 2 (a) Elementary SAW fi lter with inputoutput lOTs on single-crystal piezoelectric substrate (b) Equ ivalent circuit for an lOT based on crossed-field model

(L iN b03) and ST-X qu artz piezoelectric c rystal su bstrates were i n it ially the mainstay of SAW bandpass fi lter design Lith ium nio bate with relatively large electromechan ical coup l ing coeffi cient K2 (normal ly expressed as a percentshyage) i s e m ployed in wide-band fi lters where tem perature sensitivity is not crucial Quartz with a fi rst-order zero-temshyperature coeffi cient of delay (TCD) around room tem pershyatu re is used in narrow-band designs laquo 5 percent) req u i rshyi ng tem perature stab i l ity Table 4 l i sts i m portant fi ltershydesign parameters for these piezoelectrics together with others in use or u nder develop ment in a iming for large valshyues of SAW velocity v large K2 andor low TCD These i nclude p iezoelectric t h i n-fi l m com pos ites as wel l as s i ngleshycrystal su bstrates

In the mass-production of low-cost SAW TV-I F fi lters in Japan most are fabricated on a) s i ngle-crystal X-1 12deg Y l ithshyi u m tantalate ( i e X-cut LiTa03 with propagation 1 1 2deg from Y towards Z (see [54]) fol lowed by b) s i ngle-crystal 128deg YshyX L i N b03 ( i e 1 28deg rotated-Y cut with X-propagation) c) th in-fi lm zinc oxide (ZnO) s puttered on glass for h ighshyi m pedance devices and d) various p iezoelectric ceram ics [5] Also i n Japan some narrow-band fi lters for receiver front-ends in paging systems at 280 MHz em ploy SAW m u l-

Table 4 Some Piezoelectrics for SAW Substrates and Layered Structures

SAW Velocity K2 1st-Order TCO Substrate v (ms) () Mag (ppmdegC) Comments

ST-quartz 3158 014 0 Up to 25 cm long Ref [26] Up to 25 cm long Y-Z Li Nb03 3488

128degrotated-Y X LiN b03 3992 75 Up to 25 cm long Si02 on 128deg-Y X L iNb03 == 3800 ==80 ==0 Large K2 Ref [63] Bi12Ge02o 1681 14 120 (110)-cut (001 )-propagation GaAs lt2841 lt006 35 For (100)-cut with (110)

propagation Rotated-Y cut Z-prop LiTa03 3254 072 Minimu m diffraction cut Ref

[53] X-cut 112deg V-prop LiTa03 3288 06 18 Low bul k wave emission X-Z Li2B407 3562 ==1 62 Can dissolve in water and

acids Ref [55] ZnOAINGlass 5840 21 Uses Sezawa mode of Rayleigh

wave Ref [58]

CAMPBELL APPLICATIONS OF SAW AND SBAW DEVICES 1455

(b)

(a)

t i mode cou pl in g structu res on X-112degY liTa03 or on X-c ut Z-propagat i ng l it h i u m tetraborate (li2B407) lith i u m tetrashyborate can be troublesome to work with as it can be d isshysolved in water or acid I t has fou r acoustic modes of p ropshyagation one SAW and th ree bu l k-wave components SAW delay l i nes with 10-dB i nsertion loss at 219 MHz have been reported with TCO 6 ppmoC a good contender to replace q uartz in narrow-band appl ications [55] Berl in ite (a-AI P04) s ingle crystals have also been u nder investigation as an alternative to quartz in microwave acoustic appl icashytions [64] [65]

Whi le a va riety of crystal cuts ex ists for SAW propagation on gal l i u m arsen ide (GaAs) [39] [52] the l isti n g in Table 4

2is for the (100)-cut with (110)-propagation for maxi m u m Kand com pat ib i l ity with other GaAs-based integrated-circ u it technology [52]

C Layered Structures for SA W Propagation

Among the layered structu res e m p loying th in- or th ickshyfi l m piezoelectrics the com posite ZnOAINglass can yield

2K = 437 percent TCO = 21 ppm degC and v = 5840 ms [58] I n a device operating with less than 10-dB insertion loss at 97 MHz the above results were s imu l taneously obtained usi ng a d is pe rsion-thick ness (kH) parameter kH = 105 for the ZnO and kH = 15 for AIN [58] Sputtered p iezoelectric z in c oxide (ZnO) f i lms are polyc rystal l ine with c-axis o rishyentation hav ing a repo rted sta ndard deviation of the c-axis d istri bution around the su bstrate normal of l ess than 2 percent [56] [57] In addit ion the a l u m i n u m n itr ide (AIN) piezoelectric th in f i lm is a polyc rystal l ine sputtered one with the c-axis normal to the su bstrate su rface [58]

AIN on glass may be used as an in expensive su bstitute for sa pph i re and ceramic substrates whi le provi d i n g h igh acoustic velocity Wave propagation in t h is com posite involves the Sezawa (or leaky) su rface wave wh ich is the fi rst h igher order mode of the Rayleigh wave

SAW delay l ines operat ing above 1 GHz have also been reported usi n g epitaxial AIN fi l ms on sapph i re ( i e a lushyminum oxide A1203) as wel l as on si l icon (Si) su bstrates A TCO 0 val u e was obtained for the AINAI203 combi nation [59] Potential use of this last structu re inc lu des a SAW corshyrelator in a one-c h i p radio-frequency integrated c ircuit for a spread-spectrum transceiver [59]

Epitaxial s ingle crystal ZnO f i lms have also been em ployed in the stru ct ure (0001)ZnOSi02(111)S i usi ng fused-q uartz (Si02) where the SAW velocity could be selected from 2700shy4500 ms by changing the ZnO andor Si 02 f i lm th i cknesses [60] Com posite structu res of the ZnOSi type are of i nterest for signal processing usi ng monol ith ic SAW convolvers on s i l icon [61]

ZnO thi n-fi l m SAW video i ntermed iate frequency (VI F) fi l ters fo r color TV sets have been i n production for several years I n these devices one set of u napod ized AI i n putoutshyput l OTs is placed between a borosi l i cate glass su bstrate and a th in polyc rystal l i ne ZnO fi l m deposited by RF sputshytering [60] Additional AI th i n-fi l m cou nter e l ectrodes are deposited on top of the ZnO as shown in Fig 3(a) to al low for apod ization weighting F igure 3(b) outl i n es the strucshyture of such a com m ercial V I F fi lter using two paral l el-conshynected output l OTs for low-loss operat ion around pictu re and sou nd carriers (japan) of 5875 M Hz and 5425 M Hz respectively without a pream pl if ier The i n put l OT is stagshy

lOT

GLASSSUBSTRATE

Fig 3 (a) Placement of cou nter electrodes i n th i n-fi I m SAW device (b) Geometryof low-loss ZnOthi n-fi l m SAWVIF filter using counter electrodes (Repri nted with permission from Yamazaki Mitsuyu and Wasa see (60))

gered to p rovide the req u i red n o n l i near phase and TV adjashycent channel n u l ls for p ictu re and sou n d [60]

SAW structu res have also been fabricated to y ie ld low TCO by overlaying a th in S i02 layer with negative TCO on to a piezoelect ric substrate with positive TeO such as liNb03 or l iTa03 [62] [63] Using a th ick RF sputtered f i lm (hlA = 0310) of Si02 on 128degY-X liNb03 a TCO 0 was obta ined together with a h igh val ue of K2 = 008 [63]

I I I SAW TRANSDUCERS AND FILTER MODELING

A The In terdigital Transducer (DT) and SA W Excitation

As sketched i n Fig 2(a) the basic SAW fi lter incorporates th in-fi l m voltage-exc ited i n put and output l OTs deposited on the m i rror- l ike su rface of a p iezoelectric s ingle crystal su bstrate The t ime-varying electric fields between adjacent electrodes in the i n put l OT convert electrical signals i nto mechan ical (and b id i rectional) su rface acoustic wave (SAW) motion The converse takes place at the output l OT The penetrat ion of the SAW into the piezoelectric is about one acoustic wavelength A (eg 10 X 10 -6 m in Y-Z l i t h i u m n iobate at 300 MHz) hence the req u i rement for a h ig h-qualshyity su rface fin ish

The desi red f i ltering fu nction is ach i eved by the apod ishyzation ( i e fi nger overlap) appl ied to i n put andor output l OTs In the in put l OT the ampl itude and phase of in d ishyvidual SAW em issions are dictated by f inger ove rlap and polar ity I f appl ied i n the receiver l OT apod ization governs the relative ampl itude and phase of voltages induced in each finger pai r and the resu ltant voltage at the su m m i n g bus In the example of Fig 2(a) for an elemental SAW band pass fi lter with (nomi nal) l i near phase response the normal spac ing between l OT f inge rs of alternat i ng polarity is Ao2 at fi lter center freq ue ncy fo = vAo I f the freq uency response of the i n put l OT in Fig 2(a) is H1(w) and that of the output

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one is H2(w) the overal l res ponse H(w) wil l be given by H(w) = H1(w) H2(w) e -ii3d where (3 = 27r1A = phase con stant and d = distance between l OT phase centers The in herent delay t ime T is T = dv

The overal l device i nsertion l oss ( l L) is d i ctated by m isshymatch loss between l OTs a n d respective sou rceload im pedance as well as by secon d-order effects considered below For given l OT geometries the deg ree of mismatch loss will be dependent on the electromechan ical cou pl i n g coeffic ient K2

o f t h e piezoelectric substrate Moreover b id i rectional ity of SAW emiss ions resu lts in m i n i m u m i nsertion loss o f 3 dB per l OT o r 6-dB m i n i m u m overall

B Other Techniques for SA W Generation or Detection

While transducers employed in SAW-fi lter design are l OTs of the voltage-excited type described above other transd u cer types fi nd use i n special ized appl icat ions C u rshyrent-excited electromagnetic-acoustic transd ucers (EMATs) us ing meander l ines for SAW excitation [66] have been used for noncontact i ng i nspection of metal l ic su rfaces [67] as wel l as for the measu rement of the vertical and ho rizontal d i splacements of su rface waves [68]

SAW waves can also be generated by pulsed laser excishytation of a material su rface Th is tech n ique fi nds appl icashytion to mate rials inspection of cracks and s lots usi ng for exam ple a Q-switched Nd YAG sou rce for measur ing defect depths i n the range 01-5 mm [69] Laser excitat ion of SAW can also be appl ied to h igh-resolut ion Rayleigh velocity measu rements on SAW waves [70] [71] as well as probing SAW generation and d etection by l OTs [72] Th is laser technique has also been appl ied to p robing SAW wavegu ide convolvers to meas u re the propagation attenshyuation of specific acoustic modes [73] [74]

C Secon d-Order Effects

The performance of a SAW fi lter can be corru pted to an u nacceptable degree by any one of a n u m ber of secondshyorder effects u n less these are m i n i m ized or compen sated for These inc lude the following

1 ) Electromagnetic (EM) feedthrough between l OTs causshying i n-band and out-of-band a m p l itude and phase r i pple The level of EM feedthrough general ly increases with increas ing freq uency and can be most t rou blesome i n U H F and g igahertz SAW fi lters req u i r ing exacting packaging and avoidance of ground loops 2) Triple-transit-in terference (TIl ) associ ated with mult i pl e regene rative andor nonregenershyative SAW reflect ions between b id i rect ional l OTs which can cause excessive i n-band r ipple when the i n sertion loss is low S ign ificant red uction of TTl is ac h ieved by misshymatching sou rce andor load im pedances to their lOTs with the penalty of increased in sertion loss 3) Mass-loading by the metal l OT fi ngers causes SAW velocity changes which can alter the desi red res ponse 4) Bulk waves will rad iate from an excited I DT to some extent in addit ion to the SAW emissions These will corrupt the passband response and also red uce out-of-band rej ection S i nce the bu l k-wave component velocities are h igher than for SAW passband d istortion will tend to be most p ronounced at the h igh-freshyquency band edge particu larly in large-bandwidth (BW) filshyters ( i e BW gt 25 percent) I n Y-Z lith i u m n iobate the amount of bulk-wave generat ion relative to SAW becomes large when the nu m ber of lOT fi n ger pai rs N $ 5 cor-

CAMPBELL APPLICATIONS OF SAW AND SBAW DEVICES

responding to fi lter 4-dB bandwidth BW4 = 1 00N 20 pershycent [75] 5) Circuit factor loading resu lts from fi n ite sou rce and load i m pedances S i nce the i n put and output im pedshyances of a SAW fi lter are freq uency-dependent parameters (see Fig 2(b)) voltages developed across i n put and output l OTs are freq uency-dependent u n l ess compen sated for 6) Diffraction occu rs i n SAW l OTs i n the same manner as i n optical systems with Fresnel (near-field) a n d Fraunhofer (far-field) regions I n put and output l OTs should be in each others F resnel zone for m i n i m u m d iffract ion Its pr inc ipal effect wi l l be to increase fi lter transit ion band and shape factor as wel l as to reduce the level of close-in s idel obe suppression D iffraction is a reci p rocal effect and cannot be circu mvented by reversing the i nputoutput stages 7) Harmonics can be generated by excited l OTs in addition to the fundamental This may be a d es i rable or an u ndeshys i rable feature depending on the appl ication Harmonic freq uencies and l evels wi l l depend o n the width-space ratio of an l OT finger ( i e the meta l l izat ion ratio 1) and on the l OT geometry employed [76]-[82]

D DT Structures

I n the basic 10T of F ig 4(a) employ ing s ingle-electrode geometry and u n iform fi nger spac i ng the l OT electrode periodicity is normally such that the desired filter center freq uency fo = fSf where fo = vAo Ao = acoustic wavelength and fs is the l OT synchronous freq uency The fi nger samshypling freq uency fd i s fd = 2 fs for s i ngle electrodes altershynati ng in excitation polar ity I n the spl it-electrode lOT of Fig 4(b) fo = fs still whi le the f inger sam pli ng freq uency is now fd = 4 fs The spl it-electrode geometry of Fig 4(b) is usual ly favored over the S ingle-electrode one in normal l i near phase fi lter designs where fo = fsbull The sp l it electrodes serve to negate the spu rious response due to fi nger reflecshyt ions at center freq uency As wel l the h i gher sam pli ng freshyquency 4 fs al lows for design ing passban ds with nonsymshymet ric ampl itude an dor nonl i near phase response [83] Moreover the spl it-electrode fi nger lengths can be adj u sted to p re-distort the fi lter response for d iffraction compenshysat ion [84]

E Modeling of SA W Filters with Bidirectional lDTs

Many models have been developed to relate the freshyquency and impu lse response of l i near phase l OTs of Fig 4(a) and (b) while accou nting for the nu merous secondshyo rder effects that corru pt the ideal performance Th ree models i ntrod uced at an early date are the delta-fun ction model [85] [86] the impulse response model [87] and the crossed-field model [88]-[90] The delta fu nction neglects any seco nd-order effects in model i ng the freq uency res ponse H(w) of each l OT in Fig 2 as a transversal filter where

N -iwToH(w) = L An e n =1

where Tn = nT fo r u n iform electrode finger spaci ng and A = an e iltlgtn is the (relative) complex SAW potential assoc iated with each excited fi nger The overal l fi lter response is then

-ii3d ( ideal ly) Hin(w)Hout(w) e in term s of inp ut and output l OT res pon ses Hin(w) and Hout(w) as we l l as the p hase shift (3d between phase centers of lOTs separated by d istance d

1457

]jill nun

III IIIllnlU IIIIII

(e)

II 1i1 II III II iii mm (g)

Ii

-00 h(t) e -jhftdt (2)

H(w) e hftd f (3)

(d) ()

wil l inc rease with the f in ite n u m be r of I DT fingers employed wit h i n the f in ite-substrate length

Many network analyzers are now configu red to d isplay both freq uency response and i m pu lse response where the latter is compu ted by applying a d iscrete Four ier transform to the measured freq uency-response data Obse rvation of the i m pu lse response of a SAW device is often essentia l i n separat i n g a n d identify ing levels o f second-order effects due to EM feedthrough ITI and other spu rious SAW and bu l k-wave reflections In a d i fferent i nstru mentation approach the frequ ency-response magnitude can be obtained from the i m p u lse response without n u merical processing for d i rect display on a spectrum an alyzer [91 ]

The crossed-field model a lso y ie lds i nformation on i m pedance levels With sufficient model ing it can also accou nt for harmonic responses and ITI In this model each l OT is considered as a th ree-port structu re with two acousshytic ports and one electrical port with a 3 x 3 ad mittance matrix Y relat in g the acoustic and elect rical parameters

(h)

( i ) ( j )

(k)

Fig 4 SAW lOTs and structu res for (a) s ingle-electrode lOT

for each th ree-port Alternative approaches to modeli ng the lOT i n cl ude the

use of a scattering matrix S [92] as well as a transm ission matrix T [93] [94] The transm ission matrix can also be used to model the frequency response of SAW fi l ters using parallel-connected ban ks of b id i rectional l OTs (k nown as in terdigitated interdig ital transd ucers ( I I DTs)) for low insershytio n-loss applications such as receiver front-e nd fi lter ing [95]

F Computer-Aided Modeling

Com puter-aided design (CAD) tec h n iqu es are read i ly applicable to SAW-fi lter design on single-c rystal p iezoshyelectric su bstrates These can a l low interactive analysis and model ing of 1 ) the freq uency-d ependent acoustic conshyductance Ga and H i l bert-transform susceptance Ba in F ig 2(b) 2 ) magnitude phase and gro u p delay 3) IT I and EM

geometry (b) split-electrode lOT (c) slantedcu rved lOT on interferen ce 4) i n putoutput i m peda nces and 5) i m pu lse colli mating su bstrate-shown with exaggerated tilt (d) oneshy

port resonator (e) two-port resonator with open-circuited reflection-grating elements () two-port resonator with short-circu ited reflection-grati ng elements (g) dou bleshymetallization SPUOT (h) floating-electrode SPUOT (i) Lewisshytype SPUOT ( j) conventional comb filter (k) in-line ch i rp lOT (I) ch i rp 10T for slanted-array compressor (SAC) and (m) geom etry of a reflective array compressor (RAC) us ing etched-groove reflectors

Restrictions placed on the apodization of both l OTs are apparent with th is model

The impu lse response model yields addit ional informashytion on i n put and output i m pedance levels as well as on the frequency sensiti vity of i n d ividual electrodes This model employs the Four ier-transform relations oo

H(w) =

response [96] I n addition a variety of window fu nctions can be applied to optim ize passband response in clud ing those of the Ham m i ng Blackman or Kaise r- Bessel-type [97] [98] Some CAD programs may also be spec ifi cally appl ied to Withd rawal-we ighted l OTs [99] with sidelobe suppression of u p to about 70 dB in narrow-band fi lters (BW lt 1 pershycent) [1 00]-[1 02] where the use of a multi str ip coupler (MSC) [1 03] [1 04] is u ndesi rable

A variety of l inear-phase SAW-filter responses can also be obta ined using CAD tec h n i q ues i n corporat in g the Remez exchange algorithm or ig ina l ly appl ied to o pt i m u m l i nearshyphase digital filters These in clude SAW band pass bandshystop and am plitude-weighted eq ualizer fi lters as well as mu lt i band fi l ters with u p to 10 passbands im plem ented with in one l OT [1 05] Also t h is Remez techn ique allows the user to set the l OT syn chron ism freq uency fs outside the pass band An appropriate choice of fs fa then enables roo r-00

single-fi nger l OTs to be used without finger reflections at midband [1 05]

h(t) =

for a l i near system with a one-to-one correspo nden ce between H(w) and h(t) where h(t) is the i m pulse response This is most useful in SAW-filter design si nce the f inger overlap pattern (apod ization) of an l OT is a spatial ly-samshypled approx imation to its i m pu lse response The accu racy

G Predicting Bulk-Wave Interference

Rigorous model ing may be appl ied to p redict spu rious bul k-wave responses i n apodized l OTs One approach uses Green s function formal ism to relate piezoelect ric su rface potential and charge d ist r i butio ns over al l e lectrodes in the

PROCEEDINGS OF THE IEEE VOL 77 NO 10 OCTOBER 1 989 1458

excited l OT [13] [106] [1 07] I n anothe r tec h n iqu e appl ied to 128deg Y-X l i N b03 each mode of bul k-wave t ransport i s del ineated i n both the t ime and freq uency domain [1 08]

H Diffraction Analysis and Compensation

As noted above the effect of d i ffraction on the res ponse of a SAW band pass fi lter can be most pronou nced in the tran sit ion and stop bands The s i m plest approach to m i nshyi m izing th i s d i ffraction of cou rse is to u se l OTs with very wide acoustic apertures [109] Where th is is not feas ible d iffract ion com pen sation req u i res a knowledge of the SAW beam profi le which is dependent on the va riation of SAW velocity v with p ropagation d i rect ion Fast computations are req u i red for efficient design algorithms

Diffraction compensation has been extens ively appl ied to si ngl e-crystal ST-X quartz whose s lowness su rface about the pu re-mode SAW propagation axi s is approximated by a parabola More general non parabol ic s lowness su rfaces such as for Y-Z l ith ium niobate req u i re a fu l l angular specshytru m representation to calc u late the effect of d i ffraction [84] [ 110]-[1 1 2] The comp utation t ime for th is can becom e excessive O n e fast method for calculating SAW diffract ion i n an isotropic substrates uses an asym ptotic expan sion of the d i ffract ion i nteg ral which i s accu rate i n the very nearshyfield region Th is tec h n ique i n c reases the com putation speed by a factor of at least 25 over those fo r d i rect n u mershyical i ntegration of the d i ffract ion i ntegral [1 1 3] [1 1 4]

Magnitude and phase compen sat ion for d i ffraction are accom pl i shed by adju sting the i nd iv idual fi nger-pa i r overshylaps in the spl it-electrode l OT of Fig 4(b) together with the relative length of elements i n each fi nger pai r [84] With such tec h n iq ues i m p rovements i n s idelobe su ppression in the order of 15 dB can be attained [114]

I Modeling the Acous toelectric Field in Layered Structures

The above model ing d i scuss ions have tacit ly appl ied to SAW devices on si ngle t h ick piezoelectric su bstrates Other model s have been developed fo r l ayered struct u res propagat in g the Rayleigh (SAW) wave and h igher order acoustic modes such as the Sezawa wave l OT static capacshyitance in mult i layered devices can be computed u s i n g a tran sm issi on-l ine approach i n conju nction with an eq uivshyalence to Poissons equation fo r G reens fu nction [1 1 5] Model l ing has also been appl ied to the acoustoelectric i nteraction between su rface acoustic waves and a semishyconductor in the presence of a layer with d i fferent carr ier concentrat ion on the semiconductor su rface [116]

Appl ications incl ude mu lt i- layer th in-fi l m SAW devices on glass Si GaAs or sapph i re su bstrates One app roach appl ied to a th ree-layer structu re of ZnO and AIN t h i n fi l m s o n glass emp loys t h e same co nstitutive eq uations u sed to der ive the Rayleigh wave in a s i ngle med i u m [58] [1 1 7] Another ZnO th i n-fi l m model ta kes i nto account the crystal gra i n-random ori entation as wel l as the lattice d i stortion [118]

An effic ient iterative computational techn ique has also been appl ied to determ i n e the acoustoelectr ic field of conshyfigu rations where the l OT may be bo u nded on either s ide by an arbitrary number of layers This method i s l i m ited to mate rials of hexagonal sym m etry with the axis of s ix-fold sym metry paral lel to the l OT e lectrodes [1 1 9]


J Modeling Wide-band Linear-Phase Filters and Delay Lines

li near-phase SAW fi lters with bandwidth s of up to 50 pershycent or more have been i m plemented on l iN b03 us ing s lanted- or cu rved-fi nger l OTs as sketched i n F ig 4(c) Opershyation rel ies on the autoco l l i mati o n p roperties of l i N b03 for fi n ger ti lt angles u p to about plusmn 7deg abou t a normal to the SAW propagation axis Delta fu nction or general ized i m pu lse response model i ng may be appl i ed to obtain the transfer fu nction Differ ing i nputoutput l OT geometries can be employed to red uce passband r ipple [1 20]-[122]

IV SAW RESONATORS

A Resonator Specifications

SAW resonators employi ng reflect ion grat ings [1 23] [1 24] are employed for p recis ion f i lter ing and osc i l lator appl i shycations H igh-Q SAW-resonator osci l lators are now the preshyferred design for prec is ion freq u ency-control application i n the freq uency range 200 MHz to 1 GHz i nvolvi ng specshytrum analyzers freq uency synthesizers as well as carriershynoise test sets [1 25] [1 26] No ise floors of - 1 76 dBcHz have been reported for precis ion SAW-resonator osc i l lators [1 27] The reflection grati ngs com pr ise d of several-hu n d red perishyodic and weakly-reflect ing elements provide high reflecshytivity over narrow stop bands and al low for operation with i n sertion-loss capabi l ity of less than 6 dB Size restr ict ions normal ly l i mit the i r operat ion to a bove 1 00 MHz Q-factors attainable (Q = 1 BW) ran g i ng from ==80 000 at 1 00 MHz to 3000-10 000 at 1 GHz compare favo rably with BAW counshyterparts [1 29] For s i ngle th ick piezoelectric su bstrates SAW resonators on ST-q uartz offer excel lent tem perature stabil ity with zero l i near TCD near 25deg C and a qu ad ratic coefficient corresponding to a d rift of plusmn 15 ppm over 0deg to 55degC W h i le aging d ri fts of less than 01 ppm are attai nable typical SAW-resonator agi ng rates are between 1 and 10 ppmyear [1 32] Recent SAW-resonator designs on quartz have reported Q = 2000 for a 26-GHz resonator with i nsershytion loss less than 11 dB [1 28]

Various loss mechan isms l i mit the attai nable resonator QThese i nc lude SAW to BAW mode-conversion in the gratshyings [130] res i stive loss in the electrodes and v iscous damping i n the su bstrate Atte n u ation due to v iscous damping increases as the squ are of the freq uency It also i ncreases at low freq uencies due to i ncreased tran s m i ss ion through the fi n ite-length g rat ings [1 30] In add it ion powershyhand l i n g capabi l it ies of SAW resonators are l i m ited to a max i m u m of about 1 5-20 dBm Excessive SAW power levels lead to freq uency sh ifts of the resonator respo nse andor destructive fai l u re due to m igrat ion of the l OT meta l l izat ion by violent su rface vibrat ions

B Resonator Geometries and Modes

F igure 4(d) (e) and (f ) i l l u st rate transducer geometries fo r one-port and two-port resonators While the one-port structu res can be employed fo r d i rect replacement of some BAW crystal resonators operat ing above 50 MHz i n overshytone modes [1 32] the two-port structu res provide more design versat i l ity [131] F igu re 5 shows the freq uency response of a precis ion two-port SAW resonator operati ng at 1 GHz

1459

OC

-- 1

J

f ( r

1 v

-

r--

I ll f I V

r---

---

)

521

999 00 o MHz

-----------

Cor-

-

---------

CENTER 1 000000 000 MHz SPAN 10000 000 MHz

Fig 5 Transmission response of a precision 1-GHz two-port SAW resonator Horizontal scale 1-GHz center frequency with 10-MHz span Vertical scale 5 dBdiv Marker at 9999 MHz (Cou rtesy of Hewlett Packard Laboratories Palo Alto CA)

Centers of SAW reflections in periodic reflection gratings are at the edges of grating element Centers of reflection in excited lOT on the other hand are mid-finger positions This gives a positioning difference of AuiB at center freshyquency for metallization ratio f = 0 5 [133]-[135] (This acoustic wavelength difference is also to be found in some natural orientations of lOTs on quartz and LiNbOl [136])

Gratings have been fabricated using shallow grooves metal strips dots or ion-implanted strips to achieve the desired impedance discontinuity AZIZ [141] SAW resonator filters with up to size poles have been designed [143] As an examshyple of this technique a two-pole design at 150 MHz exhibshyited 2-dB insertion loss and 70-dB rejection at plusmn 4 MHz [144] Two-pole resonator filters on X-cut 112degY-propagation LiTa03 12BoY-cut LiNb03 and quartz are now in wideshyspread use in Japan for paging systems in the 2BO-MHz band [5] Figure 6 illustrates the compact packaging of a com-

Fig 6 Photograph of a 3 x 5-mm four-cavity SAW resoshynator chip ribbon-bonded to ceramic base (Reprinted with permission from Bray see [125])

CH2 log MAG 5 dB REF 0 dB 1 -7 1279 dB

Optimum resonator response requires correct positioning of gratings with respect to lOTs This is dictated by the magshynitude and phase of the grating reflection coefficient which is a function of the type of grating (open strips shorted strips grooves etc) as well as the substrate employed [8] [93] [137] [13B]

SAW reflections from lOTs can be detrimental to SAW resonator performance With quartz substrates this effect has been reduced by using recessed aluminum lOTs yieldshying Q values over 3200 at 1 GHz [32] In the grating reflector scattering of the SAW into bulk waves will result in increased insertion loss with a 35-dB loss demonstrated for normal incidence grating with 200 grooves and hlA = 21 percent [130]

C SA W Narrow-Band Resonator-Filters

In two-port SAW resonators single-mode operation occu rs when the resonant spacing between lOTs is reduced to support only one mode within the width of the grating stop band Mu Itimode operation can be attai ned by i ncreasshying the resonant spacing between lOTs [137] This capability has applied to the design of narrow-band SAW filters (BW == 1 percent) on lithium niobate using a staggered resoshynator structure [139] Staggered two-port SAW resonators have also been employed for harmonic operation with a Q = 2213 demonstrated for such a structure operating in the fifth-harmonic mode [140]

Narrow-band SAW filters using coupled SAW resonators have also been extensively examined for insertion loss less than 6 dB and 500 s Q s 50 000 [93] [141] [142] Resonator interconnections can include transducer multistrip waveshygu ide folded-acoustic or un idi rectional acoustic cou pi i ng

mercial 5 mm x 3 mm four-cavity SAW-resonator filter chipshyribbon bonded to a ceramic base Substrates are O5-mm thick 50-mm diameter 3B4deg V-rotated quartz with SAW propagation along the X-axis chosen to give zero TCO at 35degC [125]

D Analytic Methods

Analytical approaches to the design of SAW resonators and narrow-band filters on single-crystal su bstrates include the use of the scattering matrix S [145] cavity analysis [146] and coupling-of-modes (COM) analysis [93] [133]shy[135] One COM approach employing an unweighted 2 x

2 complex grating matrix G in conjunction with a 3 x

3 transducer matrix T and a transmission line matrix D [93] is readily extendable to the design of low-loss singleshyphase unidirectional transducers (SPUOTs) [94]

Grating reflectors can also introduce undesirable transshyverse-mode responses [147] These can be decreased or eliminated by use of tapered gratings [148] [149]

E SA W Resonators Using Layered Structures

SAW resonators have also been fabricated with layered structures For example an ZnOSi02Si layered resonator with the ZnO limited to the lOT regions (and etched-groove gratings on either the Si02 or Si) yielded Q-values in excess of 20 000 at 115 MHz [150] Resonators of this type can have temperature stabilities comparable to quartz One-port SAW resonators are also in wide use that employ a leaky SAW on 36degY-cut X-propagating LiTa03 for high K2 with moderate temperature stability In this structure the grat-

PROCUDINGS O THE IEEE VOL 77 NO 10 OCTOBER 1989 1460

75 77

ing pitch and l OT f inger spac i n g are sl ightly d ifferent with the aim of cance l ing bulk waves from grat i ngs and l OTs This design was establ is hed u s i n g a theoretical analys i s of bul k-wave rad iat ion from the grati ng reflector elements [1 51]

F Notch Filters Using SA W Resonators

A two-port SAW resonator can be configu red for either 0deg or 1 80deg phase sh ift at center frequency By con necting a su itable s h u nt netwo rk across the 180deg structu re h igh lyshyselective notch-f i lter act ion can be ach ieved Oesigns have been reported yield ing 40-d B rejection over BW = 0035 percent at 200 MHz with an i n sertion loss of 1 5 dB plusmn 1 5 dB from OC to 800 MHz [152]

V Low-Loss SAW FILTERS

A Low-Loss SA W-Filter Types

Low-loss SAW-fi lter design i nvolves some design tradeshyoffs regard less of the struct u re employed These i nc lude one or more penalties i n fabricational com plexity device size match ing networks bandwidth passband r i pple and sidelobe s idel obe suppression Apart from the resonatorshyfi lte rs considered above var ious other low-loss SAW fi lter designs i ncl ude those with m u ltist r ip couplers [103] [104] th ree-phase l OTs [153] grou p-type l OTs [154] and i ntershyd i gitated lOTs [95] [1 55]

In recent yea rs considerable i nterest has evolved in the design of low-l oss SAW fi lters for V H FUH F receiver frontshyend circu itry Low-loss fi lters are req u i red in these stages s ince the signal-to-noise performance is degraded by the amou nt of fi lter i nsertion loss This has led to a focusing of atte ntion on the use of low-loss single-phase u n i d i rect ional transducers (SPUOTs) for fi lters with fractional bandwidths BW == 1 to 5 percent Some S PUOT geometr ies are outl i ned in Fig 4(g) (h) and (i) Fract ional bandwidths of up to 10 percent have also been repo rted with a further tradeoff i n i nsertion loss [1 56] A l l o f these exploit the A8 wavelength

reflection grat i ngs placed to give the 1J8 d isplacement relshyative to adjacent banks of l OT rungs [1 61] This posishyt ioning i s dependent on whether open o r shorted g rating str ips are used as wel l as on the p iezoelectric su bstrate Typical ly each SPUOT has a total of 1 00 reflectors str ips d ivided between 1 0 l OT rungs O iffer ing rung period icities are employed in in put and output S PUOTs An insertion loss capabi l ity of IL $ 26 d B at 80 MHz has been reported for such struct u res on l ith ium n iobate with BW = 1 to 1 5 percent [94]

B Increasing Sidelobe Suppression in SPUDT Filters

A problem with u nweighted S PUOT fi lters is that the close- in s i delobe su ppression i s usual ly o n ly about 20 to 25 dB This has been increased to 40 dB i n the S PUOT of Fig 4(i) however by wei ghting the l OT rung apertu res with some trad eoff i n i n sertion loss to I L = 49 d B [156] S lanted S PUOTs have also been reported with fractional bandshywidths up to 1 0 percent [156] Moreover c lose-in sidelobe suppression of 70 dB was atta ined us ing two cascaded and weighted SPUOTs with overall i nse rtion loss I L = 85 d B a n d fract ional bandwidth B W = 1 5 percent a s shown i n Fig 7 [162]

0 -10 -20

-30 -40

rn rn0 -50 -60

Z0 E= e3Vl

-70 -80 -gO

-100 -110 -120

79 81 83 85 87 89 d ifference between the centers of transduction and reflecshy FREQUENCY (MHz)tion in an electrode of metal l ization ratio YJ = 05 U n l i ke b id i rect ional lOTs the u n i d i rect ional ity of the SPUOTs al lows match ing at both the electric and acoustic ports Also coup l ing-of-modes (COM) analysis can be read i ly appl ied to some SPUOT designs

In the origi nal SPUOT design [135] shown in Fig 4(g) the A8 transd uction d ifference parameter was obtained by using two sepa rate meta l l izations of a l u m i n u m and gold The same end result can be obtained by using a l u m i n u m electrodes o f d i ffer ing th ick ness Use o f a shadow-cast ing technique to ach ieve such a SPUOT fi lter yiel ded an i nsershytion loss IL $ 28 dB in a UHF fi lter at 500 MHz on 128degYshyX L iNbOj [157] Th i s structu re a l so exh i bited a m i n i m u m i n sertion loss of 1 5 dB at 1 GHz with a tradeoff i n inc reased passband r i pple [158]

The S PUOT of F ig 4(h) with float ing i nternal reflector electrodes comprised of open and shorted metal str ips has

(a)

(b) been reported with i nsert ion loss IL $ 23 dB and bandshywidth BW == 3 percent at 97 MHz on 1 28deg Y-X L iN b03 with e lectrode pairs in i n put and output S PUOTs Here the A8 d isplacement electrode is o btained by jud ic ious p lacement of the reflector electrodes [1 59] [1 60]

The S PUOT fi lter of F ig 4(i ) is com posed of ban ks of short

LAMIBHL APPLICA I I UNS Uf SAW AND SBAW DtVIGS

Fig 7 (a) Predicted frequency response of low-loss casshycaded SPUDT filter using COM method Horizontal scale 75-89 MHz vertical scale 10 dBdiv (b) Measured response over 75-91 MHz with vertical scale 10 dBdiv Bandwidth 15 Insertion loss 85 dB at 8277-MHz marker Sidelobe suppression 70 dB (Reprinted with permission from Campshybell dnd Saw see [162] Courtesy of Electronics Letters)

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90

V I SAW COMB FILTERS AND M U LTI PLEXERS

A Conventional SA W Comb Filters

Figure 4( j ) shows one form of a conventional SAW comb fi lter i nvolvi n g a tapped delay- l ine structu re with rungs of the same periodicity in equal i n put and output l OTs Because of the small n u m ber of electrodes per rung req u i red for b road-band o peration these fi lters have h i gh i nsert ion loss (eg 20 t0 40 dB) The bandwidths BWe of i n d ishyvid ual comb responses i n t h i s part icular structu re are BWe = O72 fofR middot W wh i le the n u m ber of comb modes M with i n

t h e overall ( s i n X)X ampl itude envelope i s M = ( WIN) + 1 I n addit ion the separation l fe between com b peaks i s l fe = fofW where W i s t h e n u m ber o f acoustic wavelengths at center freq uency fo N i s the nu m ber of finger pairs in each l OT rung and R i s the numbe r of rungs i n each l OT [8]

Such comb fi lters can f ind a variety of appl ications For example H itac h i has emp loyed a set of fo u r two-rung comb fi lters in a TV channel i n d icat ing system with freq uency synshythesizer Each TV channel n u m ber is i dentified by cou nt ing the n u m ber of comb peaks after the local osc i l l ator starts its sweep [163] In another exam ple a SAW comb fi lter i s u sed as t h e feed back element i n a m u lt imode SAW local osci l lator for a f requency hoppi ng radar [1 64] One such osc i l lator fabricated on ST-quartz operated at center freshyquency fo = 400 MHz with R = 50 rungs rung s pacing W = 40 )0 and N = 2 fi n ger pairs i n each l OT This gave M = 26 comb modes with a Q = 7lR W = 6280 for each mode [1 64]

B Low-Loss SA W Comb Filters

Wide-band low-loss comb fi lters have been reported us ing the S PUOT fi lter of Fig 4(i) but with identical l OTs in i n put and output One such comb fi lter yielded a m i nshyimum insertion loss of 3 7 dB together with a separation of 10 MHz between adjacent comb modes [165] The wideshyband capabi l ity is a consequ ence of the added signal-samshypl ing introd uced by the period ical ly-spaced reflection gratshyings desp ite the fact that each grat ing has a narrow stop band [166]

C SA W Multiplexer Techniques

SAW multi plexer action is readi ly ach ieved by u sing a broad-band i n put l OT of wide acou stic aperture to i l lushym i nate separate freq uen cy-selective output l OTs which may or may not be contiguous Freq uency measu rements of narrow RF pulses req u i re contiguous fi lter banks which should be h igh ly-selective in the freq uency domain and d i sshytortion less in the t ime domai n One approach to th is in an eight-channel design yield ing excellent performance i n both domains e m ployed flat-exponential SAW fi lters on the m i n imal d i ffraction cut of l it h i u m n iobate This yielded t i me-spurious su ppress ion in excess of 445 dB with low VSWR [167]

Another SAW mult iplexer design employs hyperbol ishycal ly-tapered i n put and output l OTs [121] [1 68] The s mallshyaperture output l OTs are positioned on either s ide of the s i ngle wide-aperture i n put l OT covering the total freq uency band I n th is way a 14-channel mult i plexer with a total bandwidth of 120 MHz (1 octave) cente red at 180 MHz achieved 40-dB out-of-band rejection with i n sertion loss I L = 1 9 d B When cascaded these fi lters yielded 80-dB out-ofshyband rejection with I L = 30 dB [168]

A qu ite d i fferent SAW mult ip l exer tec h n iq ue em ploying staggered offset half-length m u lti str ip couplers was develshyoped for a 1 6-channel SAW m u ltiplexer for range-l ine resshyolut ion in frequency-mod ulated conti nuous-wave (FMCW) mi l l imeter-wave radar This was centered arou nd an IF freshyquency of 85 MHz as s hown in F ig 8 Channel se paration

B5 FREOUENCY (MHz

Fig 8 Frequency response of 1 6-channel SAW-based mulshytiplexer for FMCW mi l l i meter-wave radar Horizontal scale 80-90 MHz vertical scale 10 dBdiv (Reprinted with pershymission from Solie and Wohlers see ref [169])

was 05 MHz with a 3-dB bandwidth of 1 MHz for eac h Range-bin widths of about 01 to 0 5 percent of range could be realized with this tec h n i que [1 69]

V I I SAW C H I RP F I LTERS

A SA W Chirp Filter Typ es

SAW dispers ive c h i rp fi lters des igned for l i near or nonshyl i near FM response are i ntegral com ponents of p u lseshycom pression radar systems Li near FM ch irps with quadshyratic phase respon se are co m monly u sed for reduced senshysitivity to Doppler s h ift whi le nonl i near ones are employed to improve the SIN perfo rmance (05-1 d B) over the fo rmer SAW l i near FM ch i rp fi lters are also u sed to i m plement variable delay l i nes real-t ime Fourier-tran sfo rm p rocessors fo r spect rum and cepstrum analys is and real-t ime adaptive filters Three types of c h i rp fi lter t ransdu cers are shown in Fig 4(k) (1 ) and (m) whi l e Table 5 i l l u strates typical SAW

Table 5 I l lustrative Saw Chirp Fi lter Parameters

Parameter Specification

Center frequency 10 MHz to 2 GHz Bandwidth B up to == 1 1 GHz Time dispersion T 10 ns to 150 -s Time-Bandwidth (TB) product up to 10 000 Phase deviation from quadratic s 050 Pulse-compression sidelobes 40 dB I nsertion loss 25 to 55 dB

c h i rp fi lter parameters and the al l- im portant t ime-bandshywidth (TB ) prod uct giv ing com pression gai n

F igure 4(k) shows an i n- l ine d i spersive transducer with metall ized fi ngers With t h i s structu re fi nger reflections and TIl normally restrict the u sable TB prod uct to TB lt 1000 Whi l e the s lanted-array com p ressor (SAC) of F ig 4(1) also has modest TB perfor mance it offers reduced degshyradation of respon se due to electrode reflect ions The reflective array com pressor (RAC) of Fig 4(m) i s employed for the h ighest TB req u i rements up to TB = 10 000 Th is RAC type can employ up to about 6000 obl ique etched groove reflectors i n each track [37] [1 70] [171] An alternative struc-


ture us ing a metal reflective d ot array (RDA) p rovides s imshypler fabrication wh i le attai n ing TB prod ucts TB = 1 000-2000 [1 72] The RAC RDA and SAC a l low for the use of a phase plate between i nput and output transd ucers to cor rect for deviations from the qu ad ratic phase response that would otherwise red uce both com p ressed-pu l se sidelobes and resolution

B Losses in SA W Up-Chirp and Down-Chirp Filters

I n pr inc i ple SAW u p-ch i rp and down-c h i rp fi lters should have the same response characteristics except fo r the change i n d i spersion s lope I n p ractice however u se of the down-chirp struct u re is prefer red This is due to several effects cau sed by electrode reflectivity On h ig h-coupl ing su bstrates piezoelectric short ing dominates caus ing changes i n SAW velocity and acoustic im pedance Massshyload ing dominates on low-co upl ing substrates such as quartz Electrode reflections i n crease the level of TTl in the ch i rp fi lter I n addit ion and as with SPUDT l OTs they int roshyduce some degree of acoustic u n idi rect ional ity into the fi lshyter perfo rmance A resu lt of this is that the down-c h i rp filshyters can have lower i n sertion loss than the ir u p-ch irp cou nterparts [13] [1 73] Moreover u p-ch i rp structures have a 33-percent bandwidth l i m itat ion imposed on their use by SAW conversion to b u l k waves [1 73] As a result pu l seshyco mpression systems em ploying both SAW expander and com pression filters often employ down-ch i rp fi lters in the transm itter (expander) and receiver (comp ressor) stages in conj u nction with spectral i nversion [174]

C Examples for Pulse-Compression Radar

l on-beam etched RACs on L iN b03 were or iginal ly employed for a i rg rou nd pul se-compression rad ar and wider bandwidth systems with typical d i s persions of T =

40 pS and co mpressed-pulse width of 200 ns [175] Imp roved tem perature stabi l ity and s idelobe su ppression can be obtai ned in the a irground systems us ing an RDA on quartz [1 70] such as the fo u r-bou nce type [172] F igure 9 is a photo of a com mercial RAC on q uartz for a radar appl ication with d i spersion T = 80 ps

As an i l l u stration of current SAC capabi l ity a SAC was reported operating at fo = 1400 MHz with bandwidth B =

11 00 MHz d i s persion T = 440 ns and TB = 484 The phase

Fig 9 Photograph of an 80-Ls quartz RAe for radar appl ishycations (co u rtesy of SAWTEK I ncorporated Orlando FL)

CAMPBElL APPLICATIONS OF SAW AND SBAW DEVICES

plate was a c h rome fi l m exposed by E-beam l ithography which red uced the RMS phase error f rom 1 71 deg to 6deg and changed the typical ch i rp slope by no more than 004 pershycent out of a total nominal val ue of 2500 MHzs Highest t ime sidelobes in the compressed pu lse were at about - 268 d B [176]

D SA W Chirp Filters for Nondispersive Delay Lines

Li near FM c h i rp fi lters are the m ost versat i le of SAW sigshynal-processing devices For exa mple a variable nond isshypersive delay l i n e was invented at an early date us ing two cascaded l i near FM SAW chirp fi lters and m ixers operat ing with spectral i nversion [177] This tech nique has been used in the 70-MHz I F stages of a sate l l ite com m u n ications l i n k t o provide adaptive cance l lation o f m u lti path s ignals arrivshying at the receiver up to 30 ps after the d i rect signal [1 78] Two down-c h i rp RACs were employed in the variable delay l i ne The i n put RAC had TB = 1200 with T = 60 ps whi le the output one had TB = 300 with T = 30 ps [1 78]

E SA W Chirp Structures for Broad-Band Filters

Li near-phase SAW-fi lter operation can be realized with equal in put and output c h i rp l OTs laid down with the same frequency-time slope [1 70] This can be part icular ly usefu l in large bandwidth designs such as i n 70-MHz I F stages of satel l ite grou nd-station receivers requ i r ing bandwidths u p t o BW = 5 0 percent Delay l i nes with octave bandwidth (i e BW = 66 percent) are a lso reported us ing slanted c h i rp fi lshyters on Y-Z L iNb03 with 2-1 0-ps delay 140-MHz bandwidth and up to plusmn 01-dB passband flatness [179] By using i n-l ine SAW c h i rp transd ucers with cub i c rather than q uad ratic phase response delay l i nes with g reater than 100-percent fractional bandwidth have been fabr icated on Y-Z Li N b03 with 39-dB u nmatched i n sertion loss [180]

VII I COD I NG U S I NG SAW TRANSVERSAL F I LTERS

A Matched Filtering Versus Correlation

Matched fi lter ing of a data bit provides a completely asynshychronous method of demod u lation with a conti nuous outshyput in t ime that represents all relat ions between signal and reference codes Correlation on the other hand fu rn ishes only one output sample at a time as a part icular val ue of the relation s h i p between signal and reference [181]

SAW-based matched fi lter ing can be i m plemented us ing fixed or prog rammable transversal fi lters (pTFs) for modest processing ga ins PG = N where N is the nu m ber of bits or c h i ps in the cod ing wavefo rm Appl ications inc lude a) matched fi lters i n sp read-spectrum com m u n ications and radar b) adaptive fi lters fo r interference m itigation c) channel equal ization i n mi crowave di gital rad io and d) radar s imu lation [40]

B Barker-Coded SA W Transversal Filters

Barker codes are bi phase codes with equal-ampl itude ti me-sid elobes with peak-to-sidelobe ratios (PSR) of 20log (N ) d B u nder pu lse compression where N i s the n u mshyber of code bits I n pu lse-compression radar these PSR valshyues wi l l of cou rse decrease away from the zero-doppler axis [183] P u re Barker codes have maxi m u m length N = 1 3 Com muni cations appl ications i nc lude use in search radars

1463

85

---+- -+-+-P r o g ro m m o Ie

ve rsion yielded a PSR 2 21 dB [1 87] Studies of PSR red ucshy Spurious Free Dynamic Range (dB) 60

where i n c reased range resolution and rangi ng accu racy are req u i red as we l l as for im proving sub-clutter v is ib i l ity whi le us ing p u l se lengths su itable for detect ion

Co mbi ned Barker codes are obtained by further encodshying each Barker bit Na with a faster Barker code of c h i p length Nbbull Whi le th is gives a process ing gai n P C =

1 0 log (NaNb) peak-sidel obe ratios with u nwei ghted codes remain at PSR = 20 10g (Na) [1 82] I t has been demonstrated however that valu es of PSR for Barker codes can be increased by we ighting the s idelobes in the energy dens ity spectrum of the autocorrelation fu nction Th is is ach ieved by inc lud ing a rec iprocal-r ipple fi lter in the SAW-fi lter design [184] U s i n g th is techn iq ue an N = 13 Barker-coded l OT (u nweighted PSR = 223 dB) on qu artz was modified to yield s idelobe su ppression of over 28 dB us ing frequencyshydomain analysis and the inverse d i screte Fou rier transform to calculate the tap weights [1 85]

C SA W lOTs For Quadraphase Codes

Quad raphase-coded waveforms can be em ployed to reduce excessive radar spectral splatter that can result using b i phase Barker-code modu lation [1 86] Barker codes can read i ly be converted to quadraphase ones for SAW l OT i m plem entat ion In th is way a SAW device on ST-q uartz with l OT geo metries for 1 3-bit Barker-q uad raphase conshy

code select ion or none Tap switc h i n g t imes are about 1 00 nSf This has been demonstrated for a program mable 1 6-ch ip coded l OT on l i t h i u m n io bate with SAW sam pl ing rate of 200 MHz Over 40 dB of tap weight was provided by the l OTs In adaptive fi lter operat ion a 1 2-MHz passband cou l d be provided about a center frequ ency tunable from 200 MHz to 300 MHz [191] In an M I T Lincoln Laboratory hybr id PTF with a fixed n u m ber of fi ngers (175 or 350) on l i t h i u m niobate the electric f i e l d s generated by t h e su rface wave are coupled d i rectly to an adjacent s i l icon c h i p with the Si02 su rface form i n g MOS capacitors [1 92] [1 93] I n d ividual MOS capacitances are fu nctions of the bias-voltage appl ied These contro l the level of RF signal coup led from i n put to output I n th is way a device with 350 taps with 30-dB on-off ratios yielded a p rogrammable bandwidth of 100 MHz censhytered at 1 75 MHz [1 92] [1 93] Table 6 l i sts some parameter values for these th ree hybrid PTFs

Table I) Parameters of SAW Hybrid Program mable Transversal Fi lters (After Ref [40))

MIT TI Hazelt ine

Bandwidth (MHz) 100 100 1 25 Du ration ( its) 1 5 008 102 TB Prod uct 150 8 1 28 Total Taps 350 16 1 28 Thermal Dynamic Range (d B) 75 50 (73)

t ion us ing rec iprocal-r ipple fi lters have also been repo rted for 5 x 5 co mbi ned Barker codes with quadraphase l OT geo metries on ST-q uartz [188]

D Minimum Shift Keying (MSK)

I n spread-spect rum system s em ploying m i n i m u m shift keying (MSK)-also known as cont inuous phase-shift modshyu l at ion (CPSM)-transmiss ions are in the form of contigshyuous signals at one of two freq uencies f1 2 = fo plusmn (NR4) =

fo plusmn (1 4Tc) where fo is the center freq uency N is the nu mshyber of chi psmessage bit R is the message bit rate and Tc i s the c h i p t ime The power s pectrum of MSK has higher s idel obe su ppression of s idelobes (23 dB) than fo r biphase modu lation th ereby cau s ing less cross-modu lation or i nterference Moreover the main lobe of the MSK power spectrum contains 995 percent of the MSK energy comshypared with 92 percent for bi nary phase-sh i ft codi n g

Using SAW technology the MSK seq uence can be read i ly generated by applyi ng either a b iphase-coded i n put seq uence [189] o r a coded i m pu l se one [1 90] to an MSKshycoded SAW l OT Us ing the latter techn iqu e an MSK genshyerator us ing an l OT with s ine (not s inc) apod izat ion opershyated at fo = 300 MHz with N = 1 27 chips per message bit at rate R = 91 Mbits with Tc = 10 8 n S [190]

E Programmable Coding with SA W Transversal Filters

Oesign co nstraints on TB p roduct dynamic range tap n u m bers and accu racy may req u ire the use of hybrid proshygrammable tran sversal f i lters for h a nd l i ng coded waveshyforms rather than fixed-tap fi lters One method reported employed by Hazelt ine is based on large-scale-i ntegration SAW (LSISAW) tec h n iqu es [40] In a Texas I nstru ments hybrid design the l OT is physical ly separate from the conshytrol electronics [191] Here du al-gate f ield-effect transi stors can be connected to either SAW l OT bus bar for 1 0

As out l ined in F ig 10 PTFs have also been i m plem ented on epitaxial CaAs us ing a (001 ) -orien ted substrate for maxshyimu m piezoelectric cou pli ng to the su rface waves and SAW propagation along a (1 10) di rect ion [52] [1 94] The h igher

n - epi tox io l loyer C o n t r o l of on S I - GoAs

A m p l i tudeP h o s e

T o p W e i g h t s

Fig 1 0 Geometric outl i ne of a progra mmable transversal fi lter on expitaxial GaAs (after Grudkowski Montress G i lshyden and Black see [52]

electron-mobi l ity and large bandgap of CaAs provide for operat ion up to about 1 CHz The SAW velocity for CaAs is 2868 ms com pared with 3158 ms for ST-q uartz whi le K2 for CaAs is on ly 38 percent less The large TCO of + 52 ppm degC for CaAs can be reduced to zero us ing th in-fi l m overlays

For PTF operation with the CaAs device a tapped FET interaction reg ion al lows d i rect i nteraction with the SAW [39] This provides m i l l iwatt power d i ssi pation per tap with h igh i n put dynam ic range low spurious signal levels and large tap onoff rat ios Also this CaAs device can be conshyfigu red for operation as a variable phase shifter a tu nable resonator or for correlation of Barker or biphase codes [52] [194]

PROC E E D I N G S OF THE I E EE VOL 77 N O 10 OCTOBER 1 989 1464

P ate f ----J Epita xia l

sllcon--- r-sllcon----- l OT

-J I D T

P o rt I n p u t

lith ium nio b ate P o rt 2 Reference

IX SAW CONVOlVERS AND CORRElATORS

A Nonlinear Operation

Th ree-port and fou r-port SAW convolvers (configu red to act as correlators) have fo u n d extensive use in spread-specshytrum com m u n icati ons and wide-band radar [46] [1 95] and more recently i n packet-rad i o systems [48] [196]-[198] These devices ope rate in a nonl i near mode u n der sufficiently h i gh power levels of SAW excitat ion [199] to correlate a s ignal u nder scrutiny with a local reference signal or code in the receiver The signal contai n s the code modu l at ion In conshytrast to the PTFs cons idered above the modulation code can be a l engthy or rapid ly-c hanging one for large p roshycess ing gai ns an dor sec u re com m u n ications Range resshyolution data rates and process ing gai n are fu nctions of the signa l-cod i n g techn iques employed Because of the l i m ited acoustic penetration depth of a SAW wave nonl i near opershyat ion of SAW-based devices can usual ly be achieved with much lower signal power levels than fo r bul k-wave devices For example SAW power levels of about 10 mWmm of acoustic aperture i n Y-Z l ith i u m n iobate represent the u p per l i mit fo r l i near operation at 1 GHz [200]

B Three-Port SA W Convolvers

Pr inc ipal comm ercial th ree-port SAW convolvers are the monol ithic waveguide (al so known as an elastic or planar convolver) type of F ig 1 1 (a) or the acou stoelectr ic one of F ig 1 1(b) S i nce these devices bas ical ly deal with convoshyI ution interactions of cou nter-propagati ng su rface acoustic waves their operation as correlators req u i res storage and recal l of a t ime-reversed repl ica of the origi nal cod ing s igshynal which is (normal ly) recal led in synchronism with the s i gnal u nder scruti ny

In these th ree-port convolvers the i n put message s ignal conta in ing the reference cod ing is appl ied to one i nput port (1) whi le the reference code is appl ied to the second in put port (2) Both in put s ignals are at the same IF carrier freshyquency f Under non l i nea r operation a c ross-cor relation res u lt is then obtai ned f rom the output port (3) at freq uency 2 f from the i nteraction of the counter-propagat ing su rface waves as measu red at an interposed metal electrode S i nce these cou nter-propagat ing waves are eq ual ly affected by temperature variations oven control of tem peratu re may not be req u i red

The convol ution efficiency 1 of a th ree-port SAW conshyvolver may be defi ned as 1 = 10 log (PouPs Prj d B m - T where Pout is the output power at Port 3 whi le P and Pr are the s ignal and i nteraction powers at Ports 1 and 2 respecshytively The trend is for Pout to be evaluated when Ps = Pr =

o dBm

C Monolithic SA W Convolver

As depicted in Fig 11(a) convolution efficiency in the monolithic SAW convolver type can be i nc reased by focusshying the SAW in to an acoustic aperture W == 2-3 A [201 ] One technique fo r achieving t h i s employs a m u ltistr ip beamshywidth compressor (BWC) [13] [201] Wide-band BWCs can be designed with loss wel l u nder 1 dB [202] Mo reover di fshyf raction compensat ion can be appl ied to the mu ltistr ip beam com pressors fo r improved perfo rmance [203] Other SAW focus ing methods em ploy horn com pressors cu rved l OTs or narrow-apertu re ch i rp l OTs [26] Beamwidth

CAM PBELL APPLICATI ONS OF SAW A N D SBAW DEVICES

PORT 1 Sig n a l

R T 2 R efere n c e

IolSC beam width com pressors

l ithium n io b ate

PORT 1 I nput coded

(a)

PORT 3 Output

sil icon layer

Air g a p 2000 A

(b)

P o rt 3 P o rt 4O u tputs

-1 1 b it 1 b it r- -4 l-N c h ip s N c h i p s (c )

Fig 1 1 (a) Outline of 3-port monolithic SAW convolver using MSC beamwidth compress ion (after Defranould and Maerfeld see [201] ) (b) Th ree-port acoustoelectric SAW conshyvolver on silicon (after Reible [45]) (c) Four-port acoustoshyelectric SAW convolver on silicon (After Reible [45])

compression also serves to su ppress spur ious tran sverse acoustic modes which can deg rade 1 by add i n g d i spersion andor reduc ing t ime-sidelobes [204]

Grou nd return planes on either s ide of the paramet ric electrode in F ig 11 (a) al low for a s ingle metal l izat ion Moreshyover the plate capacitance i s i ndependent of the plate width The Q of the output c i rcu it can then be kept low for wi de-band operation In these structu res a metal waveshyguide with acoustic aperture W = 5 A w i l l su pport th ree propagating modes at an operat ing freq uency of 300 M Hz whi le providing operation with large bandwidth and low d ispersion [202] The parametric electrode plate can a l so have u ndesi rably- large end-to-end resi stance up to several h u n d red ohms which can red uce output signal levels and a lso introduce spatial non u n i form ities Co mpensation fo r th is req u i res the metal p late to be electrical ly interconshy

1 465

nected by l eads attached at a n u mber of p laces along its length [26]

I n some designs on l ith i u m n iobate the len gth of the parametric electrode may be about one-half of the EM waveshylength at the o perat ing frequ ency T h i s can lead to standshying-wave problems u n less the strip i s properly term i n ated [26] [205] In anothe r design tech n iq ue spu rious reflecshyt ions and problems d u e to self-convol ut ion of the i n put s igshynal are m i n i m ized by u si ng two sets of i n put l OTs and two convolvi ng parametric electrodes [26]

Monol ithic th ree-port SAW convolvers on l iNb03 have been reported u s ing beamwidth com p ressors cu rved l OT focus ing [206] or smal l-apertu re focu sed ch i rp transducers with eq ual or better perfo rmance The c h i rp l OT type h as yielded a t i me-bandwidth TB = 1 615 with B = 95 MHz

referred to the in put s ignals and effi ciency 7Jc = -61 dBm at midband freq uency at 300 MHz [203]

A s ingle-track monol ithic convolver has demon strated a ti me-bandwidth TB = 2000 on l iN b03 with B = 1 00 MHz interaction t i me T = 20 lS and 7Jc = - 70 dBm [207] With a t ime d u ration of 20 lS operat ion at code rates of 90 Mch i ps wou l d then al low for the processing of codes u p to 1 800 ch ips long Model ing o f the non l i near response i n such designs has been carried out us ing variational f in iteshyelement analysis [208]

D Three-Port Acoustoelectric SA W Convolver

Figu re 1 1 (b) outl i nes a th ree-port SAW convolver employshyi ng acou stoe lectric i nteract ions with an epitaxial s i l icon layer separated by an air gap of - 2000 A [45] [209] This

des ign is attractive for very wide-band radar appl icat ions Operat ing pr inci ples d i ffe r from the waveg u i de device in terms of the non l i near m ixi ng Here non l i near m ix ing proshyduces second-harmonic voltages across the S i depletion

layer [35] [21 0] This can be u sed to obta in an increase in convol ution efficiency over the monol ithic convolver

Th ree-port acou stoelectric SAW convolvers have been engi neered to provide in put bandwidth s u p to 1 00 MHz with proce ssing gains of 30 dB (i e TB = 1 000) convol ution effishyciencies 7Jr - -55 dBm and dynamic range exceedin g 50 dB (Typical ly the dynamic range shou ld be at least 10 dB greater than the p roces s in g gai n if the effectiveness of the

latter i s to be real ized) Designs for spread-spect rum comshym u n ications and wide-band radar have been fabr icated for inp ut bandwidths of 200 MHz [1 95]

E Four-Port Acoustoelectric SA W Convolver

A fou r-port SAW convolver is sketched in out l ine in Fig 1 1 (c) I t contai n s two segme nted s i l icon elements of eq ual length Each wi l l accom modate one message bit conta i n i ng N c h i p excu rsions Th is device f inds use in spread-specshytrum com m u n icati ons wide-band radar and packet-rad io co m m u n i cations us ing MSK mod u lation (see Sect ion V I I I shy

D) of message s ignals with d i fferential phase sh ift keying (DPSK) [45] [21 1] Such d u al-s i l icon SAW convolvers have been engineered on l iNb03 fo r i n put bandwidth s up t0 200 MHz interaction lengths of 22 ls (two data bits) and ti meshy

bandwidth prod ucts TB = 2400 at IF center freq uencies of 500 MHz Convolution efficienc ies are 7Jr = -68 to - 78 dBm wh i l e the operati ng temperatu re range i s - 25 Co to + 75 C o B y co m bi n i ng th is convolver with binary-q uantized postshyprocessing waveforms can be processed with a search winshy

dow of m icroseconds for a 1 00-M Hz Signal with p rocessing gai ns in excess of 60 dB [1 95] Other spread-spectrum appl ishycat ions of the hyb rid correl ator i nclude anti m u lt ipath proshy

cess ing for data demod u lation and rangi ng Potential wideshyband radar capabi l it ies i n c lude 075-m range-resolut ion and 32 Doppler bins for each of 1280 range bins [1 95]

F Asynchronous Matched Filtering

Asynch ronous matched f i ltering of long wavefo rms can be ach ieved with SAW convolvers in power-l i m ited spreadshys pectrum system s [48] [1 95] S ignal and reference waveshy

forms are each req u i red to h ave a d u rat ion of 2 T for a SAW convolver with interaction t ime T Si nce th is req u i res no gaps in the appl ication of the reference code sam p les two SAW convolvers are needed for i m p lementation Detection

of a s ignal of u n k nown arrival t ime i s then im med iate once it has passed through the correlation interact ion area Th is technique has been appl ied to wide-band packet-rad io i ntended to provide data com m u n icat ions over a wide geoshy

graphic area [48] Packet-rad io modems have a lso been demon strated fo r a fad i n g environ ment us ing two sets of monol ithic SAW convolvers as PTFs with TB = 64 and 2000 Data rates were from 1 4 M bs down to 44 bs with almost ideal tradeoff in signal-process ing gai n from 18 dB to 61 dB [1 96]-[198]

M u lt ip le SAW convolvers can a lso be u sed to red uce the acq u i sit ion t ime of a d i rect-seq uence (OS) spread-spectru m co m m u n icat ions system This rel ies on the s i m u ltaneo u s paral lel-process ing o f d i fferent su bcod es o f a longer spread ing seq uence It resu lts i n a red uction in search time proportional to M x N where M i s the n u m ber of c h i ps

being processed in each convolver and N is the n u m ber of convolvers [21 2]

Monolithic SAW convolver structu res of ZnO-S iOrSi with high convolut ion efficiency have been repo rted [213] These structu res employed Sezawa wave propagation and exploited the nonl i nearity of the space-charge layer at the s i l icon su rface Convol ution efficiencies 7Jc = - 35 to -475 dBm were obtai ned in this way [213]

A di sadvantage to u sing the Sezawa mode of propagat ion in these structu res i s in the l i m ited bandwidth that can be achieved due to frequ ency d i spersion of the gro u p velocity The max i m u m TB = 227 obta i ned experi mental ly was close to the opti m u m avai lable value of 320 for T = 1 1 5 lS and B = 279 MHz about a center freq uency of 300 MHz [21 3]

C Cap-Coupled SA W Memory Correia tors

To date SAW-based memory correlators have not been able to com pete with SAW convolvers in provid ing TB prodshyucts of TB = 2000 (for B = 200 M Hz) in wide-band radar and

com m u n ications systems [214] Nevertheless they can f ind systems appl icat ions not h and led by the convolver c ircuishytry Reca l l that (with SAW convolver operation) the refershyence code is appl ied with pr ior knowledge of the s ignal to

be correlated aga inst There may be situations however where a copy of the s ignal code is not avai lable to the refshyerence prior to its emiss ion This is the case for mu lt i-signal sort ing and i dent ification SAW memory correlators may be u sed to com bat this deficiency si nce the correlators can be program med in one half of the carrier signal period even when the transm itted signal is a s ingle-shot one

SAW memory correlato rs can be real ized u sing the

PROCE E D I N G S OF THE I E EE VOL 77 NO 10 OCTOBER 1 989 1466

DOWN-ltHIRP (Expansion)

_ _ _ _ _ _ _ _ _ _ _ _ _ _

-------

-----------

--------

L iNbOrSi gap-co u pled device of Fig 1 1 (b) [215] or with GaAs-LiN b03 gap-coupl i ng [214] Other gap-coupled memshyory correlators i nvolve two-port variations of Fig 1 1 (b) where memory storage is ach ieved us ing either Schottky diodes [216] [21 7] or p + n d iodes i n a flash mode [218] The Schottky-d iode structure provided eight-channel operashytion with 40-MHz bandw idth and a 65-JLs delay in each channel [217]

H Other SA W Memory Correia tors

Monolithic SAW memory corre lators on GaAs have been reported on with potential capabi l ity for TB = 1000 [219] When us ing GaAs however lower correlation efficiencies are obtai ned i n wide-ba nd devices u n l ess a piezoelectric fi l m overlay is employed [220] A large scale monol ithic SAW storage correlatorlconvolver has been repo rted usi ng ZnOshySi 02-S i with h igh ly-oriented ZnO and n-type S i (1 1 1 ) together with an enhancement-mode P I-FET [221] Correshylationconvolution is performed by the FET structu re [222] Higher efficiency is ach ieved by incorporati ng piezoelecshytric oxides in the FET with self-al igned gates Devices of th is type with 35-mm length and aco ust ic delays of 1 0 JLS were fabri cated for operation at 340 MHz with i n sertion loss less than 35 d B and dynamic range greater than 55 d B [221] Another monol ithic correlator u s i ng metal-Zn O-S iOrS i has ion-i mplanted depletion in an MOS region of n-type s i l icon This structu re yielded 3-d B storage times i n excess o f 05 s [220]

I SA W-Based Acoustooptic Convolvers and Correlators

SAW-based acoustooptic (AO) tec h n iques can be appl ied to convol ution or correlation in sp read spectrum receivers [223]-[226] An AO memory convolver was reported u s i ng the acousto-photorefractive effect to store aco ust ic s ignals i n L iN b03bull In a write operati on a reference waveform r(t) is stored i n the SAW reg ion on the L iN b03 due to refractive i ndex variation when t h e laser beam is appl ied [224] A read waveform is then performed by appl ication of another laser beam conta in ing the signal mod u l at ion

An AO convolver on Li N b03 performed by us ing doubleshyd i ffract ion of the laser beam or squ are-law m ix ing in the detector for the req u i red nonl i nearity Processing gains projected for the AO co nvolver ranging from 35 to 42 dB with dynamic ranges from 45 to 52 d B are about the same as for the AO memory co rrelator [224] This structu re is outshyl i ned i n Fig 1 3(b)

One-d imensional SAW-based AO correlators are emp loyed in air-borne passive ranging to locate the range of a jam m i n g sou rce These can operate with bandwidth B = 100 M Hz with signal i ntegrat ion over 5 t0 20 ms with t ime resolution of less than 1 0 ns [227] A 2-D AO correlator has a lso been employed to cover a bandwidth B = 60 M Hz with signal i ntegration over a 30-ms period This device can detect radar returns with SIN ratios of -60 dB with Doppler resolut ion of 30 Hz [227]

X REAL-TIME SAW FOURI ER-TRANSFORM PROCESSORS

A Transform Processor Types

Three types of SAW-based Fourier-transform processors reviewed here concern a) s ingle-stage processors for realshyt ime spectral or netwo r k analysis b) two-stage processors


fo r cepstrum analys is and c) two-stage processors for onshyline adaptive fi ltering [49] Each of these techn iq ues i nvolves s ignal processing with SAW l i near FM c h i rp f i lters i n receiver I F stages as outl i ned in F i g 12

LINEAR Flot UP-CHIRP SAW FILTER 2

(Compression) 1---1

r- - - - - - --J T Bi e e

PREIotULTIPLIER LINEAR Flot SAW FILTER 1 I

l _ _ _ _ _ _ _

Impulse in Impulse in

(a)

CEPSTR U M S TAGE

I I Impu lse in L

1 st FOURIE R TRANSFORM (b)

ON-LINE

I function I(reol time)

I FOURIER TRAN SFORIot INVERSE FOURIER TRANSFORIot

(c)

Fig 1 2 (a) Real-time M-C-M Fourier-tran sform processor using three linear FM SAW chirp fi lters Con figuration here assumes no spectral inversion in mixers (b) Rea l-time cepshystrum processor employs two Fourier-tran sform operation s a n d logarithmic amplifier (c) Real-time ada ptive fi lter capashybility requires time-gating between Fou rier-tra nsform and inverse Fourier-tran sform stages (after Jack Gra bull and Colshylins [49])

B Single-Stage Fourier-Transform Processors

The s ingle-stage tran sform p rocessors im ple ment a real shyt ime Fou r ier transform S (27rJLt) operat ion for rea l-t ime specshytral or netwo rk analys i s where JL = BIT = magnitude of the l i n ear FM c h i rp slope Sonar appl icat ions i nc lude beamshyform in g and p u l se com pres sion in q u asi-real-t ime passive l i sten i ng systems as we l l as sea-bottom i maging [228] Hybrid

1467

SAWd igital tran sform processors en joy a reasonable comshypat i b i l ity for process ing signals with bandwidths up to 1 00 MHz and d u rations 1 00-200 jts (228] In such hybrid sysshytems for exa mple u p to 100 beams can be employed over the l isteni n g band from 10 Hz to 2 kHz Us ing SAW c h i r p f i lters with bandwidth B = 4 0 MHz a n d T = 100 jt s spectral resol ut ions of about 2 Hz can be real ized over 1 000 points (228]

U s i ng t h ree c h i r p fi lters with i m p ulse-d riven m u lt i p l iers as sketc hed i n Fig 1 2(a) both the magnitude and phase of the spectral response can be obta i ned As shown th i s i nvolves a c h i r p m u lt ip l icationconvol ut ionm u lt ip l i cation (M-C-M) operation to yield the Fo u r ier transform Overal l the c h i rps perfo rm the Four ier tran sform S (27rjtt) which can be decom posed as

S (27rjtt) = e - t fr (s (T) e lt )] J e -Iw dT (4)

For s impl ic ity (4) neglects any mi xer spectral in version or i n herent c h i rp l i n ear-delay terms The choice of ch irp slopes depends on whether or not spectral i nversion i s u sed i n the m i xers Spectral i nvers ion is employed i f down-c h i rp fi lters are em ployed t h roughout Post-mult ipl ication is om itted (M-C-(M)) if spectral phase is not req u i red Relative d i sshypersion t i mes for the m u lt ipl ier ch i r p (Te B) and the conshyvolver ch i rp ( Te BJ d ictate whether or not meaningful phase data is obtai nable

Real-t i m e SAW-based network analyzers of the M-C-M type can f ind appl icat ion in the co nt inuous mon itoring of transmission parameters in tropospher ic scatter and other co m m u n ications l i n ks to establ ish fad in g patterns (230] SAW com pressive receivers for power spectra on ly yield a s l id ing Four ier transform [13] [230] Opt i m u m spectral covshyerage occu rs when B = 2B and T 8 = 4T 8 with the n u m be r of resolvable output freq uencies F = T B P roshycessors with la rge n u m bers of tran sform points (eg 1024) req u i re RAC c h i r p fi lters [49]

A fou r-channel SAW com press ive receiver has been eng ishyneered to analyze a 1-GHz signal bandwidt h where each sub-channel had bandwidth B = 250 M Hz sample time T = 250 ns as well as a d u ty cyc le of 1 00 percent I h i s yiel ded an ove ral l freq uency resol ut ion of 4 MHz with a t ime resshyol ution of 500 ns and a 1 00-percent probabi l ity of i ntercept for a signal d u rat ion greater than T The design u sed idenshytical ch i rp fi lters for both c h i r p fu nct ions in an M-C-(M) structu re with t ime-grat ing of the pre m u lt ip l ier ch i rp to attain the req u i red param eters [231]

The d ual tran sform processor (C)-M-C i s e m ployed i n some appl icat ions W h i l e t h e M-C-M d evice c a n yield better SIN rat io on ly when mag n itude data is req u i red the C-M-C stru ct u re can give better dynamic range si nce weighting for s idelobe su p pression can be i ncl uded in the compressor whereas the i n put to the M-C-(M) structure must be pre-weighted to i m p rove th is [231] However the addit ional expansion loss due to spectral-energy spreadshying m u st also be considered in the choice of structu re [13]

In a (C)-M-C configu rat ion appl ied to Doppler velocity measurements of moving targets Doppler resol ut ions of 1 6 kmh relative to a stationary target were obtained using an infrared laser The convolving RAC c h i rp fi lters had TB = 400 with c h i rp-slope magnitude of 1 kHzns whi le the m u lt ip l ier RAC with the same slope had TB = 900 The specshytral resol ut ion was 84 kHz [232]

146H

The tec h n i q u e can a lso be extended to perform twoshyd i m ensional sonar and rad ar imaging [228] such as for tershyrain mapping with synthetic aperture radar Radar appl i shycations include electron ic support measu res (ESM) for rapid spectral analysis of incoming signals An appl icat ion has been descri bed of a d igital- in d ig ital-out 512 x 512 point SAW-based transformer for analyzing rea l-t ime 4-M Hz baseband s ignals The d i g ital i n put is coded into eight comshyplex b its and converted to a real-t ime s ignal with 8-MHz bandwidth and 64-Ls l i ne t i me I t i s then processed by two SAW Fou rier transformers us ing c h i r p fi lters with TB prodshyucts T1Bl = 64 jts x 8 MHz and T2B2 = 1 28 jts x 16 MHz with 27-dB process ing gai n [233]

C Use of SA W Bilinear Mixers

In some Fou rier-transform processor designs it may not be desirable to u se conventional double-balan ced mi xers since these req u i re one m i xer- input level to be held i n satshyu ration SAW b i l i near m i xers can be e m ployed instead to al low both i n puts to be control led T h i s a l lows the i n put c h i rp s ignal (wh ich can be generated d igital ly) to be ampl ishytude-we ighted for red u ction of t i me-s idelobes One such b i l i near mi xer on L i N bOJ operated with in put signal freshyqu encies of 510 MHz and 838 MHz at s ignal levels of + 23 dBm and + 26 dBm respectively with a dynamic range greater than 65 d B acoustic conversion loss of 23 dB and spur ious su ppression of 33 dB [234]

D Two-Stage Processors for Cepstrum Analysis

A SAW-based cepstru m processor is out l i ned in F ig 12(b) This i s com posed of two Four ier transformers of Fig 1 2(a) separated by a logari thmic ampl i fier By defi n i t ion the power cepstru m C (T) of a t i me-dependent s ignal s ( t) with spect rum S (w) is [235]

C(T) = I I [log l s ( t) ) 1 2)W (5)

where represents the Four ier-t ransform operat ion For situations where s (t) i s d i storted by a small period ic echo of ampl itude of (3 and de lay T the com posite power specshytru m I D (wW is ap prox imated as

I D (wW == I S (wW (1 + 2(3 cos (WT) + 32) (6)

Use of the logarith m i c a m p l i f ier al lows the signal and echo prod uct response from the fi rst stage to be separated by the output processor ( i e log (AB) = log A + log B) The output from the second transformer is in the pseu do-t ime (queshyfrency) domai n with the d i mensions of seconds

The tec h n i q u e has appl icat ions to sonar for real-t ime sepshyaration of echo reverbe rat ion as well as to radar for sepshyarat ing mu lti path i nterference With cu rrent RAC c h i rp f i l shyters with t i m e delays of 2 jts to 50 jtS and t i me-bandwidth capabi l ity u p to TB = 10 000 SAW cepstrum processors have the capabi l ity of meas u r ing pu lse d u rations from 50 ns to 50 jts Other appl icat ions in c lude the abi l ity to dete rmine

b) the code le ngth of a b in ary code or the bit rate given a

While the c h i r p fi lters in the f i rst stage of I ig 1 2(c) are configu red to i m plement a Fou rier transform those in the seco nd stage yie ld an i n verse Iou rier transform Th is sep-

VUL N U I l l UC f UK I R IYtl

a) the u n known di spersive slope of a radar c h i rp s igna l and

priori knowledge of one of these parameters [49] [236]

E Adaptive-Filter Fourier-Processor

PRUC lc lc U I N C ) lJf I H lc I f i f

I Input --- I rfs I

aration al lows for the inc lus ion of an i ntermed iate t imeshygat ing c i rc u it to perform an on-l i ne filtering function [47] [49] [50] [229] The i ntermed iate t ime-gating function h (t) i s the i m p u l se res ponse of the desi red series notch fi lter fu nction H (w) It can be configu red to act as a fixed or adapshytive notch fi lter Th is SAW-based tech n ique has an advanshytage over CCD tech nology for very wide-band com m u n ishycations with bandwidths B 1 00 MHz [50]

The filtering capab i l ity of th is real-t ime SAW transform processor for spread-spectru m comm u n icati ons has been com pared with that of a d i rect sequ ence (DS) receiver not em ployi ng a s u ppression f i lter I n one determ i nation the conventional DS receiver would req u i re a processing gain i n the range 255-51 1 to yield the same probabi l ity of error performance with a transform processor with a processing gai n of 31 [50]

SAW Fou rier-transform processors in system s for anti-jam protection may req u i re a dynamic range of 80 dB to handle variat ions of i n put power level [50] This capabi l ity was demshyonstrated i n a SAW spectrum analyzer designed for a 30-MHz i nstantaneous bandwidth and a resolution better than 1 00 kHz for an input s ignal centered at 204 MHz Th is yielded a preci s ion of 03 dB with a SIN ratio g reater than 70 dB and dynam ic range greater than 80 dB [237]

F Acoustooptic Spectrum Analysis and Computation

As an alternative to the SAW compressive receiver which provides outputs serial ly i n t ime SAW-based i ntegratedshyoptics spectrum analyzers ( (OSA) em ployi ng SAW Bragg cel l s f ind appl ication at i n put freq uencies 1 GHz where there is a close match between SAW and optical fields with bandwidth capabi l ity lt 1 GHz [26] [28] The SAW Bragg cel l s can b e employed i n h ighmiddotspeed A O computing systems [38] [238] [239] I n the acou stooptic (AO) spectrum analyzer depicted in Fig 1 3(a) the Fourier transform i s a spatial one

Photodiode Arra

Diffracted Ligh _

-- -

LiN b03 Lens lOT

(a)

Photo-Detector

PORT 2 INPUT INPUT

LiN b 0 3 Beam

(b)

Fig 1 3 (a) Outl ine of acoustooptic spectrum analyzer (after Tsai [38]) (b) Outl ine of acoustooptic convolver on LiN b03 (after Becker Reible and Ralston [224])

CAMPBELL APPLICATIONS OF SAW AND SBAW DEVI CES

i m plemented by an optical lens on a piezoelectric s u rface Here l ight from a laser d iode is confi n ed to the su rface region by an i n put planar lens Bragg diffraction of the l ight beam then res u lts from its i nteraction with the period ic refractive i ndex changes due to the SAW from an excited I DT which can be a ch irp one for wide-band operation [240] The angular d i str ibution of Bragg deflected l ight is subshyseq uently transformed by the second lens with a l i near array of receivi ng photod iodes along its focal plane [26] [38]

Most of these devices reported to date have employed L iNb03 substrates which only a l lows for hybrid packaging Recent stu d ies have been appl ied to GaAs wavegu ides for total or monolithic integration with laser d iode sources and photodetectors [239]

X I SAW OSC I LLATORS AND FREQUENCY SYNTHESIZERS

A SA W Oscilla tors and Types

SAW osc i l lators are fi nd ing ever- increasing appl ication i n precis ion i n stru mentation [1 25] com m u n ications and radar by virtue of their merito rious featu res of a) high specshytral purity b) fundamental freq uency capab i l it ies from 100 MHz to 2 GHz or more c) smal l s ize and weight and d) low power d ra in with max i m u m RF powers in the range up to

20 dBm Delay-l ine or resonator-type SAW osci l lators with low vibrat ion sensit ivity and aging rates of less than 1 ppm year offer freq uency stabi l it ies com parable with those of low-freq uency BAW osc i l lators and su bstantial improveshyments over mu lt ipl ied BAW osci l lators [1 25]-[129]

In this paper SAW osc i l lators with two-port configu rashytions [131] [132] are grou ped into th ree types accord i n g to their design as 1 ) s i ngle-mode fi xed-freq uency sou rces 2) s i ngle-mode voltage tu nable sources or 3) those with m u lshytimode capabi l ity

B Single-Mode Fixed-Frequency SA W Oscillators

These fi nd appl icat ions as com pact freq uency sou rces i n preci s ion i n strumentation com m u n ications and radar c i rshycuitry For freq uencies below 1 GHz SAW osci l lators u s i ng high-Q resonators yield the best stab i l ity perforshymance whi le SAW osci l lators em ployi ng delay l i nes have compatible stab i l ity perfor mances at h igher freq u encies [241]

low phase-noise performance can be attained us ing h ighshyqual ity free-ru n n ing SAW osc i l lators An alternate way of attai n i ng low-noise performance however is by inject ionshylocking an osci l lator with poor phase noise to a low-noise sou rce With th is techn ique the overal l noise perfo rmance i s ent i rely that of the i njection sou rce [242] An inj ectionshylocked SAW osci l lator has also been employed as a central component in the design of a U H F FM demodu lator with improved FM threshold perfo rmance [243]

The ag ing rate of SAW resonators i n SAW osci l lators i s a fu nction o f t h e operating power level varying from a few pp myear to gt 1 000 pp myear [244] Moreover at power levshyels above about 20 dBm (depe n d i ng on the design) excesshysive resonator su rface v ibrat ions wi l l l ead to migration of the I DT al u m i n u m metal l izat ion which can cause device fa i l u re with i n a few m i nutes [245] This migration can be i n h ibited to some extent by u si ng an AICu al loy fi l m rather than pure AI in the I DT metal l ization [244]

1469

Sou rces of noise in oscil lators i n c lude pertu rbati ons d ue

to oneor more of a)wh ite phase ( f) f l icker ph ase (11f) wh ite freq u ency (11f2) fl icker freq uency (1 1f3) and random walk (1(4) with freq uency-dependent spectral s lopes ind icated White freq uency and fl icker frequency are due to pertu rshybations with in the bandwidth of the feed back loop cau sed by wh ite and fl icker phase noise respectively [246] Ranshydom wal k noise relates to long-term aging

Whi le the predo m i n ant noise i n most SAW devices i s fou nd t o b e t h e 1 1 f f l icker phase o n e SAW resonato rs are invariably fo und to a lso have a 1f2 contri bution wit h i n 1 0 - 2

Hz of the carrier frequency [247] [248] The level of noise

in quartz resonators can be dependent on transducer metal l izat ion u sed [249] as we l l as f i lm stress [250] SAW devices on l iN b03 substrates can also exhi bit an addit ional bu rst noise of varying d u ration [247]

By way of i l l u strat ing h igh-performance capabi l ity a stashy

bi l ized 310-M Hz SAW osc i l l ator was reported with a noise floor of - 1 76 d BclHz at 20 kHz Fou rier-freq ue ncy offset This employed a SAW resonator on q u artz with Q = 12 000 The acoustic apertu re of the resonator was 148 10 whi le its

effective cavity len gth was 370 10 The large resonator s u rshyface area was em ployed to red uce m igrational stress levels in the AICu l OTs at an operat ing power level of +20 dBm The pea k stress level of 34 x 1 07 Nm2 was wel l i n s ide the h igh aging l evel for pu re a l u m i n u m l OT metal l izat ion [127]

The stabi l ity performance of SAW osc i l l ators i s crit ical ly dependent on the in herent tem peratu re sensit ivity of the crystal sub strate One way of com bati ng th i s i s to ensu re

that the crystal is held at a constant tem peratu re in an oven with low thermal t ime constant Another technique em ploys tem perat u re com pensation with mU lt ip le resonators [251] A th i rd approac h u ses a piezoelect ric with two SAW delay l i nes on AT quartz The delay l i n e with 10w TCD is employed in the osci l lator loop The other delay l ine is at an angle to the fi rst along a h igh TCD axis Th is forms part of a temshyperatu re-sensing and m icroprocessor-control c i rcuit and adj u sts the phase sh ift around the osc i l lator loop to comshypen sate fo r tem peratu re changes This techn ique reduced the tem perature-ind uced frequency-d ependent variation from plusmn 125 ppm to plusmn 1 4 ppm over a tem peratu re range of

-23deg to 75degC in a system operat ing at 300 MHz [252]

C Tunable SA W Oscillators

SAW voltage-co ntrol led osc i l lators (VCOs) f ind appl icashyt ion in VHFU H F com m u n ications for mobi le and cel lu lar rad io where both precis ion tunabi l ity and stabi l i ty are req u i red over a large n u mber of channels with n5-kHz o r 25-kHz separat ion and - 70-d B a n d - 80-dB adjacent-chanshynel selectivity F igure 14 is a photograph of a com pact comshymercial SAW VCO Most SAW VCOs employ a fi xed SAW delay l ine in series with a vol tage-co ntrol led phase sh ifter in the feedback loop Whi le quartz is the preferred delayshyl i n e substrate l iNbO can be used to reduce the feed bac k ampl if ier gain req u i red U se of th i s latter su bstrate req u ires the feedback loop to be locked to a low-freq uency BAW crystal osc i l lator [256] with a phase-noise m u lt ip l ier-ratio

20 log (n) where n is the freq uency m u l t ip l ier rat io [257]

Variable SAW delay l i nes have also been fabri cated with sputtered zinc oxide on an oxid ized n-s i l icon substrate with freq ue ncy sh ift of 560 ppm [253] Tu nable SAW delay l i nes and two-port resonators are also reported on epitaxial GaAs [52]

Fig 1 4 Photograph of a compact commercial voltage-conshytrolled SAW osci l lator (cou rtesy of SAWTEK I ncorporated Orlando FL)

Typical SAW VCO specif icat ions for mobi le rad io wo u l d cater f o r a t u n i n g range of u p to == 1 percent output power of 4-5 dBm and a phase noise of - 1 25 d BclHz at a Fou riershyfreq ue ncy offset of 10 kHz from the carrier Th in- or th ickshyfi l m hybrid construct ions can be employed Thick-fi l m hybrid SAW osc i l lators have been reported for t h e freshyq uency range 750-1500 M H z with freq ue ncy settabi l ity of

plusmn 10 ppm [254] [255] Use of a d i fferent ial SAW delay l i ne with a MOSFET conshy

trol ler in the feedback loop offers a possible improvement in l inearity of t u n i ng respon se over the standard type [258] Also a tu nable SAW osc i l lator with th ree delay l i nes and a l i m iter i n the feedback loop i s reported with a tun ing range of about 1 1 7 percent with no mode hoppi ng even when the osc i l lator was tu ned over several modes [259]

D Multimode SA W Oscilla tors

M u lt imode osci I lators fi nd appl ication in freq uency-agi Ie radar Freq ue ncy agi l ity perm its decorrelation between

radar echoes from s uccess ive p u l ses as wel l as a red uction of c lutter inten s ity [260] A m u lti mode SAW comb osc i l lator centered around 400 MHz h as been descri bed for the localshyosc i l lator stage of a freq uency-ag i le rad ar Each com b l OT on the ST-X quartz su bstrate had 50 rungs s paced by 40 10 with two electrode fingers per rung This su pported 21 comb modes spaced 1 0 M Hz apart (see Section VI-A) Com b-freshyq u ency selection was made us ing a varactor-tu ned fi lter i n t h e feedback loop [164] Another freq ue ncy-selection techshynique e m ploys tem porary forced-i njection of the desi red freq uency us ing SAW l i near FM chirp fi lter m ix ing [261] Also low-loss SPU DT-type comb fi lters can be u sed i n oscilshylator feedback loops to provide red uced osc i l lator phase noise over that obtai ned us ing conventional comb fi lter cou nterparts [1 66]

E SA W-Based Frequency Synthesizers

A fast freq ue ncy-hopping system fo r spread-s pect rum co m m u n ications has been descri bed which is based on freshy

q uency m ix ing us in g i m p u l se-d riven l inear FM chirp f i l ters of oppos ite slope [262] The desi red CW signal (p l u s a host of intermod u lation prod ucts prior to fi lteri ng) is obtained as a su m-or-difference mixer output when the m ixer i s

PROCEE D I N G O F T H E I E E E VOL 77 N O 1 0 OCTOBER 1989 1470

d riven by the two impulsed c h i rps The CW s ignal is l i nearly dependent on the time delay between the impu lse excishytations [262] A reported system used doubly-d ispersive in-l ine chirp filters on ST-X q uartz with d ispersion T = 1 0 p sa n d ch i rp s lope magnitude p = 48 MHzs Fast frequency hopping was obtained at 200 khops to any of 240 channels i n either of two bands at 356-404 MHz and 306-354 M Hz Potential ly this tech nique should allow for up to 400-hop freq uencies over the 500-MHz bandwidth [262]

Another frequency-synthesis technique employed a comb generator us ing a step-recovery d iode to d rive SAW fi lter ban ks on ST-q uartz with n ine SAW filters per ban k over the frequency range 1 369-1 606 M Hz with tone spacshying of 1 MHz and switc h i ng speed less than 1 00 ns [263]

X I I SAW FILTERS IN DIGITAL COMMUNICATIONS

A Systems Components

SAW oscil lators and filters are used in many sections of microwave digital radio and satel l ite dig ital-commun icashytions l i nks [264] [265] I n sate l l ite-commun ications l i n ks us ing phase-shift-keyed (PSK) d ig ital mod u lation they are to be found in the d igital mod u lator (SAW osci l lator) bandshywidth l i m iting (SAW filter) and u p-converter stages (SAW VCO) in the transm itter as wel l as in the down-converter (SAWVCO) noise bandwidth l i m iting filter (SAW filter) and d igital demodulator stages (SAW VCO) of the receiver [264] I n m ic rowave d igital rad io for the common-carrier bands at 4 6 and 11 GHz with bandwidths of 20 30 and 40 MHz SAW filters play an im portant role in spectral-shaping of 70-MHz or 140-M Hz IF stages in conju nction with spectrallyshyefficient d igital-mod u lation tech niques such as q uad rashytu re-am pl itude-m odu lation (QAM) [266]-[268] At th is ti me 16-QAM and 64-QAM m ic rowave digital rad ios (em ploying SAW Nyqu ist fi lters) have been engineered whi le 256-QAM systems are under development

In long-haul optical-fiber data-com m u n ications l i nks operating at bit rates from 1 00 Mbits to over 1 000 Mb its SAW filters are employed in the clock-recovery c i rcu its for regenerative repeaters operating at freq uencies up to the 1-GHz range [269]

B SA W Nyquist Filters

U nder the Nyqu ist bandwidth theorem b i nary data can be transm itted through an ideal low-pass or l inear-phase bandpass channel on an error-free basis (Le without i ntershysym bol-interference ( 15 1)) at a rate equal to twice the fi lter cutoff frequency Practical fi lters with non rectangular passshyband shapes can sti l l tran smit with negl igible 1 5 1 at this rate however provided that the fi lter transition band rol loff i in accord with Nyqui sts vestigial sym metry theorem [270] Typically this req u i res a 50 percent excess bandwidth over the ideal one

Matched fi lter ing req u i res the Nyq u ist fi lte r function to be split eq ually between transm itter and receiver Moreshyover for avoidance of 1 5 1 with rectangular pulse trai ns with (s in X )X 2 power spectral d istribution a compensating spectral shaping fi lter with X(s in X ) ampl itude response is additionally req u i red i n the transm itter U sing SAW techshynology th is spectral-shaping filter can be i ncorporated with the portion of the Nyquist fi lter i nto one com posite fi lter in the transmitter


Since SAW fi lters for Nyq uist and spectral shaping in microwave d igital rad io m ust meet stringent specifications if the bit-error-rate (BER) is to be m i n imal this means that bul k-wave interference d i ffraction and I DT end-effects m ust also be m i n i m ized To this end some such SAW-fi lter designs em ploy V-l ine I DTs with offset apod ization as shown in Fig 15 where fi ngers with short overlaps near the

Fig 15 A V-l ine I DT with offset apodization (Reprinted with permission from Vigil Abbott and Malocha [272])

ends of the I DT have negl ig ib le cou pl ing to ground [271 ] [272]

The use of two weighted I DTs coupled by a m u lt istr ip coupler can be advantageou s for precision SAW Nyq u i st fi lters with large fractional bandwidth O ne design for a 70-MHz Nyqu ist filter with 74-percent bandwidth on 1 28degshyrotated L iNb03 had ampl itude and group delay ri pples of 02 dB and lt 1 0 ns respectively The design em ployed a second-order com pen sation algorithm which was appl ishycable to I DTs with up to 1 000 fingers [273] A 1 40-MHz SAW I F filter for a 1 6-QAM digital rad io operat ing at 1 40 Mb its with = 50-M Hz bandwidth on 128deg-rotated L iNb03 exh i bshyited negl igible 1 5 1 [274]

C Clock Recovery In Optical-Fiber Communications

SAW fi lters are considered to be the most mature techshynology available for clock-recovery in regene rators in longshyhaul optical-fiber com m u nications at data rates from 1 00 Mbits to over 1 000 M bits [269] Practical Q ranges 500 Q 800 req u i red for these systems d ictate the u se of transshyversal filters rather than resonators with phase-slope ratios of 2 to 3 and a maxi m u m freq ue ncy detuning al lowance of 02 rad [269]

X I I I SAW ANTENNA DUPLEXERS

Nonci rcu lator types of antenna d u p lexers con sist of transm itter and receiver fi lters connected in paral lel to a common transm itreceive anten na In mobile and cel lu l ar co mmu nications the tran smit fi lter must have low insershytion loss with power-hand l i n g capabi l ity up to 2 W or more The receive fi lter mu st also have low insertion loss as wel l a s good side lobe suppression Wh i le t h e receiver SAW fi lshyters are read i ly designed the problem has been to engi neer the SAW transm itter fi lter to withstand h igh power levels without breakdown

SAW-based antenna d u plexers are now being employed in U H F portable telephones for cel l u lar rad io transceivers [275] Under EIA standards fo r Class I I portable telephones they must withstand = 35-d B m ( = 33-W) i nput power level These 800-MHz devices are fabricated on a 2 x 2-m m 36deg YshyX LiTa03 chip in a TO-5 package Their in sertion loss i s about 1 -1 2 dB with output handl ing powers o f up t o 2 W

1471

7J7l7

----i (illl Mot

C

lt l -H uP =

I

I-

-LL

S m11 1 I I I IJG I

I

Out

Piezoelectric Substrate

Fig 1 6 High-power transmit fi lter for UHF antenna duplexer u ses cascaded SAW resonators (Repri nted with perm ission from Hokita Ish ida Tabuchi and Ku rosawa [275])

The h i gh-power transmit f i l ter is constructed with elecshytrical ly-cascaded SAW resonators as sketched in Fig 1 6 with 300-400 l OT fi nger pairs in each resonator The reson ators them selves are not conventional h igh-Q types but wideshyband ones operat in g on a pr inc ip le s i m i lar to that of a laser with d istri buted feed bac k [275]

In the above du plexer metal l ization of the h i gh-power wide-band resonator fi lter u ses alu m i num with 1 5-25-pershycent copper doping [275] By us ing sputtered a l u m i n u mshytitan i u m (AITi) metal l ization with 04-08-wt percent Ti however ladder-type SAW fi lters for anten na du plexers in mobi le telephone transceivers have operated in the range of 3 W at 835 MHz [4]

X I V SAW SIGNAL PROCESS ING ON GALL IUM ARSENIDE

A Bias for lOTs on CaAs

While l OTs can be fabricated without modification on semi-i nsu lat ing GaAs those depos ited on epitaxial GaAs must be b iased to form Schottky barriers Biasing is used to deplete the mobi le charge carriers in the reg ion beneath the l OTs so that they do not short out the e lectrical f ields between excited electrodes With this mod ification matched f i lter ing program mable f i ltering or p rogramshymable syn c h ronous correlation can be im plemented on GaAs with in tegrated-c i rcui t compat ib i l i ty [39] [52] In a reported program mable SAW fi lter on n-type GaAs with a carrier concentration of 1 x 1016 cm - 3 segme nted-FET c i rshycu itry was used for tap select ion FET sou rce and d rain conshytacts were o h m ic whi le the float in g gate electrode formed a Schottky barrier Reversal of the dc bias changed the outshyput phase by 1800 [39] [52] Moreover in SAW resonator designs on epitaxial GaAs voltage control of the dc b ias on the resonator sections a l lowed for a t u n i n g capabi l ity by control l i n g the transm ission phase through the reflection grati ng Such a structure a l lowed a freq ue ncy tu n i n g of 89 ppm in a SAW oscil lato r fo r a bi as voltage change of 1 8 V [52] I n another GaAs fi Iter design operati ng at 300 M Hz with bandwidth B = 30 M Hz a quad ratu re arrangement of two PTFs o n the same substrate al lowed for control of both the ampl itude- and ph ase-weighting for each tap [276]

B Acoustic Charge Transfer (ACT) Devices

SAW-based acoustic charge tran sfer (ACT) devices on e pitaxial GaAs have been u n der i ntense developme nt in recent years for appl icat ions such as to program mable

(a)

+ 8V RtreclO1 Stull

I I

CGoAs

(b)

tapped delay l i nes [277] high-speed sam pl i ng paral lel-serial storage and convolvers [41 ] [278] ACT convolver operation is reported with a t ime-bandwidth prod uct TB = 400 with B = 160 MHz together with a spur ious-free dynamic range of 37 d B and sig nal-to-noise ratio SIN = 37 d B [279]

Operation of an ACT on GaAs evolves from SAWCCD devices fabri cated on L i N b03 where the SAW created a trave l l ing potential wave at an adjacent depleted Si su rface [280] Monolithic charge transport SAW devices us ing metal ZnOSi02Si have also been reported [281]

In the i l l u strative ACT structu re of Fig 1 7 a metal f i lm plate (biased for Schottky-d iode o perat ion) serves as a

367 MHz 367l MHz

(c)

Fig 1 7 (a) Side view of ACT structu re on GaAs (b) Transshyport charge potentials (c) Charge in jection and detect ion (Repri nted with permission from Hoskins and Hu nsi nger [41])

charge-transport channel to the output port In operat ion SAW waves from the excited (and biased) i n put l OT create trave l ing potential wel ls at and below the piezoelectric s u rshyface which transport the charges at the SAW velocity [41 ] F igure 1 8 out l i nes an ACT program mable delay l ine with

SAW Drive

Input

Address Buss

DC Power Deloy Select (Oi9itol)

Output

Fig 1 8 Schematic of an ACT progra m mable delay l i ne (courtesyof E lectron ic Decis ions I ncorporated U rbana I ll

taps to the Schottky transport plate Such structu res can al low for delay ranges of 96 ns to 813 ns in sta ndard prodshyucts with up to 1 28 delay sett ings at tap spaci ngs of 56 ns over bandwidths of B = 1 50 MHz with 35-dB spur ious-free dynamic range and power consu m ption lt 5 W

PROC E E D I N G S OF T H E I E EE VOL 77 NO 10 OCTOBER 1989 1472

I n another ACT design tech n ique the charge is transshyported i n a heteroj u nction chan nel layer of (AI Ga)AsGaAs (AI Ga)As This ACT has the potential for higher dynam ic range as wel l as for i ntegrated-ci rcuit compatibi l ity with field-effect transi stors [282]

An ACT structu re has also been reported us ing a p-type GaAs transport channel plate on an n-type channel layer Th i s al lowed for the d i rect optical injection from a 5145- A

laser beam gated by an acoustooptic mod u l ator [283]

xv SAW SENSORS

A Sensor Classification

Sensors may be classified with i n the framework of s ix catshyegories [44] These relate to 1) Measurands (eg acoustic chem ical) 2) Technological Aspects (eg resolution senshysitivity) 3) Detection Techniques (eg biological magshynetic) 4) Sensor Conversion Phenomena (eg biochemical transformation photoelastic) 5) Sensor Materials (eg organ ic piezoelectric) and 6) Fields of Application (eg automotive space) SAW sensors have been engi neered to measu re mon itor or control a n u m ber of chem ical and physical parameters such as gas concentration [284]-[287] desorption of organic vapors [288] acceleration stress and press u re [289]-[291] electrostatic potential [292] magneticshyfield strength [293] acoustic absorption [294] and transshyverse acoustoelectric voltages for nondestructive characshyterization of sem iconductor s u rfaces [295] Usual ly the parameter u nder study is determi ned by cau sing it to pershyturb the electric or acoustic characte ristics of a SAW delay l i ne in a meas u rable way The d elay-l ine pertu rbations can be measu red d i rectly as for the case of sem iconductor s u rshyface characterization through a SAW-sem icond uctor i ntershyaction [295]

Where the pertu rbation effect is very weak or can not be measu red d i rectly its level can be ded uced from the freshyq uency change produced in a SAW d elay-l i ne osc i l lator I n magnetic-field SAW sensors fo r exam ple the SAW-osci lshylator frequency sensitivity i s 70 Hzgauss [293] I n accelershyation measu rements on ST-q uartz delay-l ine osci l lators freshyq uency sens itivities in the order of 10- 7g have been reported [291] H ighl ights of some of these tech n iques are given below

B SA W Chemical Gas Sensors

A typical approach to chem ical sens ing is to cause the gas to alter the freq uency of a SAW delay-l i n e osci l lator with sens itivity theoretically increasi ng with frequency [284] The aim here is to su itably sensitize the delay-I ine s urface to give maxim u m change in osci l lator frequency which is u sual ly constrained to be less than 300 M Hz A change of gas conshycentration causes a change in s u rface mass This affects the acoustic field of the SAW It also affects the conductivity of the su rface layer and thus the electric field of the SAW

One SAW gas sensor e m ployi ng this technique u ses two isolated delay-l i ne SAW osc i l lators and ST-X q uartz subshystrates [285] One of these is affected by the measurement while the other acts as a reference sou rce The dual conshystruction thus al lows for fi rst-order co m pe nsation for temshyperatu re h u m i d ity aging inf luences etc The d elay-l ine su rface on the meas u ri ng device is coated with a chem ical i nterface i n the form of an organic sem icond uctor (physhyhalocyani ne) for measur ing N 02 gas concentration Gas


i nteraction with this s u rface causes a change i n SAW velocshyity v and delaY T The freq uency d iffe rence is then a measure of gas concentration Sensitivities of 1 00 Hzppm N02 at an operating freq uency of 3948 M Hz were reported with a threshold sensitivity of about 05 ppm [285]

Another d ual SAW-osci I lator c ircu it for measu ri ng hyd roshygen su lphide (H2S) employed twin SAW delay l i nes fabrishycated on a s ingle L iN b03 substrate In this case the sen s i ng SAW delay l i n e was coated with a fi l m of activated tungsten trioxide Th i s sensor was fou n d to respond to concentrashytions of H2S of less than 1 0 parts per b i l l ion [286]

C Electrostatic Surface Voltage Sensors

To ensure clean copies electrostatic s u rface potential measu rements are requ i red to mon itor and control the electrostatic su rface potential of the photosensitive drum i n a paper-copying machi ne One technique used for this measu rement e m ployed an FM-mod u l ated SAW delay- l ine osc i l lator [292] The delay l ine was on 1 28deg Y-X L iN b03 and incorporated an add itional col lector electrode d riven by a vi brating mod u l ator The output from an FM demodu lator then changed l i nearly with electrostatic h igh voltage Th i s sensor h a d i n put i mpedance over 1 012 0 with high sensishytivity and i m m u n ity to overload [292]

D Touch Panel Sensor

An economical touch panel has been reported using SAW absorption The touch system emp loys i nput and output non dispersive reflective arrays for S ingle-freq uency opershyation Th is is in conjunction with i nput and output wedge transd ucers u s i ng thickness-reson ant slabs of piezocershyamic attached to one side The refl ective arrays cause the output s ignal to be a composite of a l l the SAW components having d ifferent transit ti mes Appl ication of a finger to one poi nt of the i ntermed iate su rface space causes a dip to appear i n the output signal at a t ime which is a fu nction of the horizontal position of the touch [294]

E Acceleration Stress Compensation

Acceleration and vibration can i n d uce stress in a SAW delay l ine or resonator and seriou sly pertu rb its freq uencyshyresponse characteristics This is acceptable of cou rse if the aim is to sense these changes In other SAW osc i l lator deSigns however it may be necessary to min i m ize accelshyeration and vibrational sens itivity I n a SAW device or oscilshylator su bject to acceleration load i n g it is thus necessary to have a precise knowledge of the su bstrate geometry crystal orientation and mounting

In related stud ies it is reported that an STC-cut SAW device fabricated on a rectangular plate wi l l have accelshyeration sensitivities of less than 1 0 -9g (in terms of gravishytational g) expressed as a fract ional change in resonant freq uency [289] [290]

XVI SAW DEVICES IN SCANNING ACOUSTIC MI CROSCOPY

A SAM and SLAM Microscopes

Scann i n g acoustic imaging has i m portant applications to the nondestructive testing of microelectronic devices and industrial materials as well as biomed ical d iagnosis Such imagi ng systems are configu red as either scan ning laser

1473

I I I I I U I iTjill l

acoustic mi croscopes (SLAM) or scann ing acoustic m ic roshyscopes (SAM) [296] SAM system s f ind pr inc ipal appl ication in the sub-su rface imag i ng of opaq u e objects [297] In both of these i maging techn iqu es d i sti l led water is the most com mon fl u id used for cou p l i n g the u ltrasound to the area u nder observat ion with an absorption loss of 22 d Bmm at 1 00 MHz at 220 d Bmm at 1 G H z [296]

B SAM Imaging

A major problem with the SAM i maging technique is in e l i m inating strong su rface reflections from the l i q u id-su rshyface interface These can be reduced by operat ing the SAM in a pu lse mode us in g RF excitation pulses i n conj u nct ion with t ime-gat ing to remove spu rious echoes [297] For objects with weak reflectivity Signal-level enhancement can be i m p roved by operat ing with chi rped RF pu lses The pulseshycompression SAM ope rates in analogous fashion to SAWshybased pulse-com pression radar H ere the expander waveshyfo rm passes t h rough an aco u stic focus ing lens and l i q u i d interface t o the object u n der study T h e reflected signal i s then processed by a SAW compressor ch i rp fi lter in the receiver Mechan ical o r electrical scann ing control can be employed

Us ing SAW c h i rp fi lters with d i spersion Tand bandwidth B yields a processi n g gai n TB with compressed pulse width B - 1 bull For maxi m u m resolut ion therefore it i s desi rable to ope rate with large-bandwidth SAW ch i rp fi lters However the maxi m u m usefu l c h i rp fi lter bandwidth also depends on the fi lter center freq uency em ployed With this l i m ited to about 1 GHz because of losses in the cou p l i n g f lu id the usable bandwidth is about 300 MHz [297]

C SA W-BA W Mode Conversion Imaging

Experim ents are reported on a 100-MHz SAM where object-scann i n g for a two-di m ensional image rel ies o n a grat ing scanner Th is grat ing scanner mode-converts s u rshyface acoustic waves into bu lk acoustic waves to i m plement a d i rected beam of acou stic energy Th is was ac h ieved by scattering a non l i near ch i rped SAW from a cu rved periodic grat ing of 350 metal strips on Y-Z L iN b03 as shown in F ig 19 to obta in a scan ni ng-l ine focus of bu lk longitudi nal

Lith ium gtNon linear ch irp niobate l OT

Fig 1 9 A SAW-BAW mode-conversion i maging techn ique for scanning acoustic microscopy at 100 MHz (after Chen Fu and Lu [298])

waves as a transm itter with a wide-band bu lk probe transshyducer as a receiver The SAW nonl i near ch i rp fi lter operated arou nd 100 MHz with T = 1 3 Jls and B = 50 MHz This yielded real-t ime imaging with a resolut ion of 70 Jlm with a scanning velocity 3500 ms The f ie ld of v iew was 10 m m with a u n iform ity better than 1 dB [298] Two-d imensional aco u stic

mapping is a lso repo rted us ing a l eaky SAW on 1 28deg V-X L iNb03 [299]

XVI I SHALLOW BULK ACOUSTIC WAVE (S BAW) DEVICES

A SBA W Requirements and Piezoelectrics

The operation of shal low b u l k acoustic wave (S BAW) devices req u i res efficient propagation of such waves close to the p iezoelectric su rfaces as depicted in Fig 20 [300]

I D T I D T

Fig 20 I l l ustrating su rface sk imming bulk wave (SSBW) and su rface transverse wave (STW) polarization and propshyagation

[301] To achieve this the selection of both the piezoelectric and its crystal or ientation m u st satisfy a n u m ber of criteria This i ncl udes req u i rements for large coupl ing coefficient for the SBAW zero beam-steeri ng above and below the su rshyface zero TCD together with zero (or m i n i mal) co u p l i n g t o SAW or other bu lk waves [42]

Both SBAW and SAW devices em ploy l OTs I n some i n stances the two device types can be visual ly ind ist inshygu ishable from one another For exam ple operation i n one or the other mode on ST-q uartz merely i nvolves the choice of a d i fferent crystal ax is for wave propagat ion Moreover SBAW devices can have a n u m ber of relatively attractive features over the SAW ones

a) SBAW velocities are higher than SAW ones I n 90degshyrotated ST-q uartz the SBAW velocity is about 1 6 h igher than for SAW For the same l ithograph ic capashybi l ity th is i n creases the device u ppe r-freq uency capabi l i ty by the same factor

b) I n some cuts of quartz and LiTa03 SBAW devices have lower TCD than their SAW cou nterparts

c) S i nce the SBAW p ropagation is below the piezoshye lectric su rface th is offers red uced sensit ivity to su rshyface contam i nation as wel l as better aging perforshymance in osc i l lator appl icat ions

d) SAW resonators and delay l ines can operate at m u ch h igher powers than SAW cou nterparts before the on set of p iezoelectric non l i nearities

e) Some SBAW devices can have red uced spurious responses

f) SBAW can have lower propagation l oss than SAW at mic rowave frequ e ncies

Table 7 i s a l ist of some SBAW crysta ls and orientations for s i ngly-rotated cuts as shown in Fig 21 (a) Tem perature com pensat ion of the 90deg-propagat ing si ngly-rotated qu artz as wel l as f ine-tun ing of device freq uency has been obtai ned us ing a th in-fi l m SiOz overlay [303]

Doubly-rotated cuts of qu artz with axes shown in Fig 21 (b) have also been exam ined for SBAW appl ications with part icular attention to the SC-cut [304] The doubly-rotated cut is de noted ( YXw1 )ltigtO where the angle cgt gives an extra degree of freedom and also a l lows for o pt im ization of other

PROCEEDINGS O F T H E I EEE VOL 77 N O 1 0 OCTOBER 1989 1474

---I LaJL

gtlt-___ -

() 35 45

33

plusmn 55

sBAW Velocity K2 Euler Angles TeD

Table 7 I l lustrative sBAW Piezoelectrics and Parameters (After Refs [43] [302])

Crystal (ms) A p () (deg) (ppmdegC)

35deg rotated Y-cut LiTa03 X-prop

4221 47 0 0

5937deg rotated Y-cut 4802 167 0 3793 0 L iNb03 X-prop

Rotated Y-cut sT- 4990 1 89 0 13275 90 quartz

+355deg (AT) rotated 5100 1 44 0 12515 90 plusmn 1 27 Y-cut quartz ( - 55 to +85degC)

-505deg (BT) rotated 3331 04 0 41 90 Y-cut quartz ( - 55 to +85degC)

SAW C U T S SSBW CUTS BT- cut B T - cut Z - a xis

AT -ATshycutcut

q u a rtz q u a rtz

V- axis V-axis

(a)

y

X (b)

Fig 2 1 (a) Rotated-Y cuts o n quartz f o r SAW and ssBW use (after Lewis [42]) (b) si ngly- and doubly-rotated crystal cuts (after Bal lato and Lu kaszek [304])

parameters [304] Berl in ite has also been under study for SBAW appl ication

B Surface Skimming Bulk Waves Devices

Devices em ploying SBAW propagation are also referred to as su rface sk imming b u l k wave (SSBW) ones when no wave-trapping grat ing is employed between input and outshyput l OTs i n Fig 20 [42] [43] I n model ing the impulse response h (t) of an SBAW filter relative to its SAW counshyterpart it has been shown that the two are related by h (t)SSBW ex h (t)SAWJi in terms of res pon se t ime t [42] For an u nashy

2podized SSBW l OT th is yields the same (s in X)X power dependence as for a conventional SAW delay l i ne [305]

Ante n na theory may be appl ied to a model ing of the freshyqu ency response of the SBAW l OT [42] One reason for this is that SSBW motion is c losely related to that for Love waves Bl uestei n-Culayevwaves and those on corrugated su rfaces [306] In a l l of these last-mentioned propagation mechashynisms acoustic energy is confi n ed to the su rface reg ion by a s lowing mechan ism such as a grat ing or su itable su rface layer I n the SSBW device on the other hand the surface confi nement resu lts from the act ion of the excited i n put l OT as an end-fire antenna array d i rect ing the acoustic energy to the output one The received power varies at 1R in terms of path length R [42]

Also in terms of antenna theory an equ ivalent c i rcuit model can be obtained for the radiation resistance of a


SSBW l OT and transducer capacitance which is s i m i lar to the in-l i ne model u sed for some SAW devices [42] [43] A major d i fference however is that the effective coupl ing of the SSBW is i nve rsely proportional to -IN (N = finger pairs) wh i le the cou pl ing is i ndependent of N i n the SAW case [43] Also SSBW l OTs with spl it electrodes have been found to be more d i rective than those us ing s ingl e ones [307]

A problem that can arise in the design of SSBW devices relates to the spu rious wave reflections from the sides of the crystal particu larly s i nce the reflectivity of SSBW is high and it i s d ifficult to damp out reflected waves by us ing absorbers on the crystal su rface For BT-cut quartz it has been shown that only one propagating wave is reflected from an unmetall ized crystal side s ince the shear horishyzontal wave is the slowest one i n this c rystal For LiN b03 two wave com ponents are reflected si nce the shear vertical one is the slowest in this med i u m [308] [309]

Wide-band SSBW delay l i nes have been reported us ing a m u ltistrip cou pler (MSC) in conjunction with two apodshyized l OTs on 35deg rotated V-cut LiTa03 and 37deg rotated V-cut LiN b03 These devices had en hanced spurious b u l k wave rejection and tem perature stabi l ity over their SAW cou nshyterparts [310] U n l ike a SAW device however 1 00-percent SSBW power transfer is not performed by an MSC Th is is due to u nequal strengths of symmetric and antisym metric mechan ical vibrational under the MSC stri ps [31 1]

The insertion loss of the SSBW d evice is the sum of th ree cont ributions due to input and output l OTs (as for a SAW device) with an added loss due to acoustic power-spreadshying [43] S ince the power loss wi l l i ncrease by an additional 3 d B for every doubl ing of the path length SSBW devices are not su itable for delays longer than about 1 00 A For shorter delays i n sertion-loss performance is com parab le with those for SAW fi lters SSBW fractional bandwidths BW = 03-2 percent on qu artz and B W = 1 5 percent on LiTa03 have been re ported with i n sertion l oss 13 dB and sideshylobes gt 55 dB with TCD 0 for the first-o rder and secondshyorder delay coefficients [43]

SBAW delay l i nes and h igh-O oscil lators have been reported us ing AT-q uartz delay l ines with I L = 34 dB at 31 CHz and fifth-harmonic BT-q uartz delay l i nes with I L = 35 d B at 22 C Hz The freq uency-O prod ucts fO 68 X 1 012

are wel l above those reported for SAW delay- l ine devices [302]

C Use of an Energy-Trapping Grating

Without compensation energy loss can be excessive i n SSBW delay l i n es and fi lters for l OT acoustic separations

1475

OC

--

17

1

[ JV r1 1 VV lr-A III

V v v

A V I I V f

V

V - - --- --

C H 1 greater than about 1 00 A [304] Loss reduction can be ac hieved however by u se of a su rface slowing layer such as a Si02 fi lm on rotated V-c ut qu artz [312] or by an energyshytrapping grat ing or corrugated su rface between I DTs [306] SBAW devices in corporat ing such trapping structu res are referred to as su rface t ran sverse wave (STW) ones when the acoustic wave motion is predomi nantly shear-horizontal (SH)

U n l ike SAW su rface transverse waves can have a conshytrol lable depth of propagation i nto the piezoelectric subshystrate Th is depth of penetration is dependent on the design of the energy-trappi ng grati ng I ncreasing the metal strip th ickness resu lts in trapping the SH wave more closely to the su rface l ead i n g to in creased diffraction and i nsertion loss [313] [314]

In th ese designs it i s des i rable to m i n i mize the acoustic power dens ity s ince the FM noise floor of an osci l lator varshyies inversely with the squ are root of the osc i l lator power [31 3] whi le the aging perfo rmance worsens with increasing power l evel [244]

STW propagation has been exam ined on corrugated surshyfaces for groove depths hA from 075-1 37 percent and 501 or 701 grooves [31 5] as wel l as with alu m i n u m stri p gratings of va rious height-to-period ratios [31 3] STW propagation un der a metal-str ip grat ing d i ffers from that un der a grooved one [31 3] Whi le both the metal strips and grooves slow the SBAW the metal str ips have an additional s lowing effect due to the d i fferent shear-wave ve locities in metal and subshystrate This effect is s i m i lar to the slowi ng of a Love wave along a q uartz su rface with a th in metal f i lm overlay [31 3] As wel l the load ing of the i n putoutput I DT electrod es themselves can affect the shape and mutual posit ions of the stopbands for the periodic I DT electrodes [316]

D STW Resonators and Oscilla tors

Two- port STW resonators em ploy reflect ion grat i ngs and an energy trappin g grat ing as sketched in F ig 22 Here the period 0 of the e lectrodes i n the reflection grat i ngs is the

ifimmli liIDImil EN ERGY- TRAP PING

GRATING Fig 22 A two-port STW resonator employing an energyshytrapping grat ing for low-loss operation

same as for the I DT f ingers The period O2 of the grating strips corres ponds to O20 sl ightly less than u n ity

Whi le theoretical Qs as h igh as 1 60 000 are pred icted for two-port STW resonators on isotropic su bstrates [318] meashysu red val ues to date are typical ly in the 5000 to 10 000 range F igure 23 shows the measu red response of a 1 726-G Hz STW resonator on V-rotated qu artz fabricated with E-beam l ithography and a l i ftoff process with l i newidth 074 It m reflection grati ng period 1 48 It m un loaded Q 5600 and i n sertion loss 1027 dB [31 7] Packaged STW resonators operat ing at 500 MHz and 632 MHz showed insertion loss less than 6 d B and Qs as h i gh as 1 2 000 [31 7]

Measurements on a 640-MHz SA W resonator osci l lato r

52 1 l o g MAG 5 dBI REF 0 dB 1 - 1 0 2 79 dB 1 726 50 o MHz

Cor

CENTER 1 726 0 00 000 MHz SPAN 20 000 000 MHz Fig 23 Transmission response of a 1 726-GHz STW resoshynator on Y-rotated quartz Fabricated with E-beam l i thogshyraphy and l ift-off process L inewidth - 074 tm and pitch - 1 48 tm Qu - 5600 IL = 1027 dB (Repri nted with pershym i ssion from Bagwel l and B ray [31 7] )

operat ing at a power level of + 24 dBm showed an im meshydiate decrease in reson ant freq uency A 632-M Hz STW resshyonator operating at + 26 dBm however showed no appreshyciable ch ange in Q or freq uency after 49 days of h igh-power operation [31 7] Fl icker phase (1 1f) noise performance i n STW resonators was fou nd t o im prove with expos ure to h igh operat ing powers exh i bit ing device noise l ess than - 1 35 dBcHz at 1 Hz Fou rier-frequency offset This may be comshypared with typical 11f noise levels of - 1 1 5 to - 1 35 dBCHz at 1 Hz offset in com parable SAW devices [31 7]

As with SAW devices SBAW ones can also be configu red to operate in harmonic modes [31 9] [320] In demonstration of this a harmonic grou p-type STW fi lter on AT V-rotated quartz was fa br icated without sub-m icron l ithography for operation at the third-ha rmonic freq uency of 1 1 3 GHz with in sertion loss I L -26 to - 30 dB [321 ] I t has been shown however that the in sertion loss of such harmonic STW devices is critical ly dependent on the th ickness of the ene rgy-trapping grating increas ing as m u ch as 50 d B when the grat ing th ick ness is increased by a factor of fo u r [322]

XVI I I D I SCUSSION

Over a period of 20 years the SAW-device f ield has grown i nto a matu re tech nology exten d ing in to nu merous areas of electron ics and com m u n icat ions In so doing the techshynology has had a su bstantial in f lue nce o n RF systems arch ishytecture and packagi ng such as in the u se of hybrid modshyu les This has led to red uctio ns i n syste ms costs s ize and weight with particular i m pact on mobi le and portable elecshytron ic systems [7] A recent example of th is capabil ity relates to use of SAW devices in secu re automobi le ign ition sysshytem s 1 n one such system an i ndividual ly-coded SAW strucshyture is actual ly embedded in the ign ition key I n sertion of the key causes a SAW-encoded signal to be sent to an elecshytron ic i nterrogation modUle and then to the engine control com puter Use of the wrong key wi l l prevent the engine from start ing up

SAW tech nology is now being routinely u sed for co m plex

PROCEED I N C S OF THE I E E E VOL 77 N O 10 OCTOBER 19R9 1476

signal-processing techniq ues in both analog and dig ital com m u n ications systems The sophistication of both design and fabrication techniques is now such that SAW fi lters are being bu i lt to meet specificat ions on ampl itude and phase response that wou ld have been considered u n real ist ic j ust a few years ago [7] In part this is d u e to read i ness by which many improvements i n semicond uctor microelectronic fabrication and l ithographic tec h n iq ues can be adapted to the SAW-d evice field

SAW-device capabil ity has also been responsible for s h ift ing I F signal processing to s ign ificantly h igher freshyq uencies than those l i m ited by conventional I u m ped or d i sshytr ibuted inductance-capacitance netwo rks This is attracshytive i n that it al lows for a wider bandwidth capabi l ity as wel l as for reducing or el i m i nating spu rious m ixer s ignals i n I F stages With their h igh I F freq uency capabil ity SAW fi lters will undoubted ly play a vital role in the design and develshyopment of I F stages for h igh-defin ition TV (H OTV) with fi rstshyI F stages operating at or above 900 MHz [7]

Another SAW appl ication area which (if successful) cou l d resu lt i n a d ramatic increase i n cu rrent production levels relates to the use of SAW tran sd ucers as passive elements i n electromagnetical ly-scanned electro n ic packaging labels i n locations where optical-scan n i ng can not be employed or is impractical In operation the label package wou ld include a SAW fi lter with ampl itude- or phaseshyweighted l OTs attached to an RF anten na In operation the label is scan ned by an EM Signal yielding a re-radiated RF signal that repl icates the l OT cod i ng for label detection

Shal low bulk acoustic wave (SBAW) device tec hnology is about 1b years you nger than that fo r the SAW field Al ready SBAW devices have proved to be most attractive in comshypetition with SAW ones in areas of resonators and precis ion osc i l lators G iven the yardstick of SAW-device developshyment fo r com pari son the next few years should be imporshytant ones for real izi ng the fu rther potential of SBAW devices

ACKNOWLEDGMENT

Th is study was supported in part by an operating grant to the author from the Natural Sciences and Engineering Research Cou nci l of Canada

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[312) J Z Wilcox and K-H Yen Shear horizontal su rface waves on rotated y-cut quartz IEEE Trans Sonics Ultrason vol SU-28 pp 449-454 Nov 1981

[313) D F Thompson and B A Auld Su rface transverse wave propagation u nder metal str ip gratings in Proc 1986 IEEE Ultrason Symp vol 1 pp 261-266 1986

[314) D L Lee Analysis of energy trapping effects for SH-type waves on rotated y-cut quartz IEEE Trans Sonics Ultrason vol SU-28 pp 330-341 Sept 1981

[315) A Renard J Henaff and B A Auld SH su rface wave propshyagation on corrugated su rfaces of rotated y-cut quartz and berl in ite crystals in Proc 1981 IEEE Ultrason Symp vol 1 pp 123-127 1 981

[316) E J Danicki Propagation of transverse su rface acoustic waves in rotated y-cut quartz substrates u nder heavy perishyodic metal electrodes IEEE Trans Sonics Ultrason vol SU-30 pp 304-312 Sept 1983

[317) T L Bagwel l and R C Bray Novel su rface transverse wave resonators with low loss and high Q in Proc 1987 IEEE Ultrason Symp vol 1 pp 31 9-324 1987

[318) A R0nnekleiv High Q resonators based on su rface transshyverse waves in Proc 1986 IEEE Ultrason Symp vol 1 pp 257-260 1986

[319] D L Harmon F Josse and J F Vetel ino Su rface skimming bul k waves i n y-rotated quartz-Experimental characterizashytion and filter device implementation in Proc 1979 IEEE Ultrason Symp pp 791 -796 1979

[320] K F Lau et al Further i nvestigation of shal low bu lk acousshytic waves generated by using i nterdigital transducers i n Proc 1977 IEEE Ultrason Symp pp 996-1001 1977

[321) R Hugl i GHz SAW and STW bandpass filters without subshymicron geometries using harmonic group type un id i recshytional transducers in Proc 1987 IEEE Ultrason Symp pp 183-187 1987

[322) R L Baer and C A Flory Harmonic operating of STW filshyters in Proc 1988 IEEE Ultrason Symp 1988

Colin K Campbell (Fellow I EEE) was born in St And rews Scotland in 1927 At the age of 15 d u ring World War I I he trained as a Radio Operator for the British Merchant Navy and at 17 volu nteered for active sershyvice with the Royal Corps of Signals British Army From 1946 to 1948 he was a Comshymunications Engi neer with the Foreign Office London England the British Embassy Washington DC and the British Delegation to the U nited Nations New

York He has also served in the m i l itary forces of Canada and from 1 962 to 1968 was Commanding Officer of 201 U niversity Squadron Royal Canadian Air Force

He attended MIT twice on scholarships i nc luding the Massashychusetts Golf Scholarship and obtained an SM degree in elecshytrical engi neering there in 1953 fo r a thesis on power and machines He also holds an Honors BSc degree in electrical engineering

CAMPBEll APPLICATIONS OF SAW AND SBAW DEVICES 1483

(1952) a PhD degree in low-temperatu re physics (1960) from St And rews University Scotland and a D Se in engineering and appl ied science (1 984) from the Un iversity of Du ndee Scotland As a graduate student i n 1 959 hewas an I nvited Member of the British research student delegation at the Meeting of Nobel Physics Prize Win ners in Lindau Bavaria

An experi mental ist by t ra in ing and inc l ination he has cond ucted research in a wide range of fields inc luding low-temperature su perconductivity giant-pulse lasers dielectrics power-elecshytronic devices VLS I m i l l i meter-wave instrumentation and d isshytrib uted-parameter devices He has publ ished n u merous papers on SAW devices as wel l as a textbook on SAW signal processing

Dr Campbell is a Fellow of The Royal Society of Canada a Fellow of The Engi neering Institute of Canada a Fellow of The Royal Socishyety of Arts (England) and a Member of Sigma Xi He holds The I nventor ins ignia awarded by Canadian Patents and Development Ltd as well as th ree C itat ions for outstanding contributions to un ishyversity teaching and education In 1983 he was the fi rst electrical engi neer to be awarded the Thomas W Eadie Medal of The Royal Society of Canada for major contributions to engi nee ring and applied science in Canada

He was with McMaster Un iversity Ham i lton Ontario Canada from 1960 to 1989 where he was a Professor of electrical and comshyputer engi neering He is now an i ndependent consu ltant

PROCE E D I N G S OF THE I E EE VOL 77 NO 10 OCTOBER 1989 1484

Table 1 Representative Applications of SAW Devices

Device Applications

Medium loss SAW filter IF filtering Clock recovery (nondispersive) Nyquist filters MSK

modulation SAW delay line Path length equalizers Altimeters

Pressure and temperature sensors Tunable oscillators Recirculating storage

Fixed-tap delay line Pulse compression radar Barker and quadraphase coding Radar return simulation

Programmable Adaptive filtering for spread transversal filter spectrum Matched filtering

Channel equalization Radar simulator

SAW Comb filter Multiplexers Multimode oscillators Counters

Low-loss SAW filter VHFUHF front-end filtering Mobile and cellular radio Antenna duplexer

SAW resonator Precision filters and fixed oscillators

SAW chirp filter Pulse compression radar Variable delay lines and multi path cancellation Real-time Fouriershytransform processors Wideshyband linear-phase filters Reflective array compressor with large TB product

Three- and four-port Matched filtering in spread SAW convolver spectrum Long-code

correlation Radar Packet radio Acoustic charge High-speed sampling Wide-band

transport on GaAs pn-code correlator Programmable filtering

Other SAW devices on Tunable delay lines and GaAs resonators Programmable

filters and correlators SAW-based Bragg modulators Spectrum

optoelectronic analyzers Wide-band devices convolvers and correlators

Monolithic integration on GaAs

Multilayered SAW Rugged resonators and filters devices Monolithic SAW convolvers and

correlators Sensors

Table 2 Some Current Applications of SBAW Devices

SBAW Type Applications

SSBW devices Mid-loss filtering with reduced sensitivity to surface contamination Operating frequencies up to about 60-percent higher than SAW-based counterparts

STW devices Low-loss filters Resonators with highershypower capability than SAW Stable oscillators

Moreover SBAW filters can be configured with center freshyquencies up to about 60-percent higher than with SAW devices using the same piezoelectric substrates and transshyducer geometries

Many features of SAW-device technology can be readily transferred to SBAW implementation since they involve the same microelectronic fabrication and production proshycesses and may use the same piezoelectric materials Some SBAW devices can be visually indistinguishable from their SAW counterparts differing only in the piezoelectric crysshytal orientations employed

Mechanical wave propagation in SBAW devices is often referred to as surface skimming bulk waves (SSBWs) when only input and output IDTstructures are involved In SBAW resonators incorporating energy-trapping gratings the wave motion is usually termed a surface transverse wave (STW) one Table 2 lists signal-processing applications of both of these SBAW-device types

B Aim of this Paper

In this paper the salient features of significant SAW and SSBW devices are reviewed in terms of their device paramshyeters and performance It is assumed that the reader has some knowledge of SAW device principles For the SAWshydevice review emphasis is given to developments over the past 10 years I nterested readers seeking more background material are referred to a n umber of textbooks deal ing with various aspects and treatments of this su bject [8]-[20] Early key papers on SAW devices are to be found in [21]-[23] Also other review papers deal with SAW filters [24] components for electronic warfare receivers [25] SAW-device applicashytions [26]-[29] SAW resonators [30]-[32] SAW materials [33] SAW waveguides [34] SAW waves and acoustoelectric interactions [35] [36] SAW reflective array structures [37] acoustooptic Bragg modulators for integrated optic comshymunications [38] SAW-based fixed and adaptive filtering on GaAs [39] hybrid programmable transversal filters [40] and SAW-based acoustic charge transport (ACT) processes and structures on GaAs [41] Principles of SBAW propagation and devices are contained in [42] and [43] A sensor classhysification scheme is presented in [44] The use of SAW conshyvolvers in spread-spectrum communications is reviewed in [45]-[47] with wide-band packet radio emphasized in [48] Specifics of SAW Fourier transform processors for intershyference rejection in spread-spectrum communications adaptive filtering real-time spectrum and cepstrum analshyysis for radar and sonar are in [19] [49] and [50] SAW and SBAW propagation in gallium arsenide are examined in [51] and [52]

Open-literature publications on SAW and SBAW devices are largely documented in a) IEEE TRANSACTIONS ON ULTRAmiddot

SONICS FERROELECTRONICS AND FREQUENCY CONTROL and its precedessor IEEE TRANSACTIONS ON SONICSAND ULTRASONICS

b) annualEEE Ultrasonics Symposium Proceedings c) PROshy

CE EDINGS OF THE IEEE and d) Proceedings of the Annual Freshyquency Control Symposium In view of the mass of literashyture on these subjects to date references in this paper mainly relate to the first three sources

II SAW CRYSTALS AND LAYERED STRUCTURES

A Representative SA W-Filter Specifications

Key parameters for nondispersive SAW bandpass filters with typical commercial specifications are shown in Table 3 The choice of piezoelectric substrate is basic to attainshyment of such specifications involving tradeoffs between insertion loss filter fractional bandwidth temperature stashybility and shape factor (SF) where SF = tfrll1 f such that I1f = bandwidth at 1-dB points I1f = ultimate rejection bandwidth (and SF = 1 is ideal) Figu re 1 shows the response of a precision commercial SAW filter for 70-MHz IF opershyation


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1459

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gtlt-___ -

() 35 45

33

plusmn 55





4221 47 0 0






AT -ATshycutcut

q u a rtz q u a rtz

V- axis V-axis

(a)

y

X (b)

















1475

OC

--

17

1


V v v

A V I I V f

V

V - - --- --













Cor












ACKNOWLEDGMENT


REFERENCES









































1477













































































































































































































































































































OC

-- 1

J

f ( r

1 v

-

r--

I ll f I V

r---

---

)

521

999 00 o MHz

-----------

Cor-

-

---------













D Analytic Methods








75 77











0 -10 -20

-30 -40

rn rn0 -50 -60

Z0 E= e3Vl

-70 -80 -gO

-100 -110 -120




(a)





1461

90












B5 FREOUENCY (MHz

































1463

85

---+- -+-+-P r o g ro m m o Ie









MIT TI Hazelt ine












T o p W e i g h t s







-J I D T

P o rt I n p u t









o dBm




PORT 1 Sig n a l

R T 2 R efere n c e


l ithium n io b ate

PORT 1 I nput coded

(a)

PORT 3 Output

sil icon layer

Air g a p 2000 A

(b)






1 465


































_ _ _ _ _ _ _ _ _ _ _ _ _ _

-------

-----------

--------














(Compression) 1---1

r- - - - - - --J T Bi e e


l _ _ _ _ _ _ _


(a)

CEPSTR U M S TAGE

I I Impu lse in L


ON-LINE



(c)




1467









146H






C(T) = I I [log l s ( t) ) 1 2)W (5)


I D (wW == I S (wW (1 + 2(3 cos (WT) + 32) (6)










I Input --- I rfs I






Photodiode Arra

Diffracted Ligh _

-- -

LiN b03 Lens lOT

(a)

Photo-Detector

PORT 2 INPUT INPUT

LiN b 0 3 Beam

(b)














1469














































1471

7J7l7

----i (illl Mot

C

lt l -H uP =

I

I-

-LL

S m11 1 I I I IJG I

I

Out










(a)

+ 8V RtreclO1 Stull

I I

CGoAs

(b)




367 MHz 367l MHz

(c)



SAW Drive

Input

Address Buss


Output







xv SAW SENSORS




















1473



B SAM Imaging












I D T I D T













---I LaJL

gtlt-___ -

() 35 45

33

plusmn 55





4221 47 0 0






AT -ATshycutcut

q u a rtz q u a rtz

V- axis V-axis

(a)

y

X (b)

















1475

OC

--

17

1


V v v

A V I I V f

V

V - - --- --













Cor












ACKNOWLEDGMENT


REFERENCES









































1477













































































































































































































































































































75 77











0 -10 -20

-30 -40

rn rn0 -50 -60

Z0 E= e3Vl

-70 -80 -gO

-100 -110 -120




(a)





1461

90












B5 FREOUENCY (MHz

































1463

85

---+- -+-+-P r o g ro m m o Ie









MIT TI Hazelt ine












T o p W e i g h t s







-J I D T

P o rt I n p u t









o dBm




PORT 1 Sig n a l

R T 2 R efere n c e


l ithium n io b ate

PORT 1 I nput coded

(a)

PORT 3 Output

sil icon layer

Air g a p 2000 A

(b)






1 465


































_ _ _ _ _ _ _ _ _ _ _ _ _ _

-------

-----------

--------














(Compression) 1---1

r- - - - - - --J T Bi e e


l _ _ _ _ _ _ _


(a)

CEPSTR U M S TAGE

I I Impu lse in L


ON-LINE



(c)




1467









146H






C(T) = I I [log l s ( t) ) 1 2)W (5)


I D (wW == I S (wW (1 + 2(3 cos (WT) + 32) (6)










I Input --- I rfs I






Photodiode Arra

Diffracted Ligh _

-- -

LiN b03 Lens lOT

(a)

Photo-Detector

PORT 2 INPUT INPUT

LiN b 0 3 Beam

(b)














1469














































1471

7J7l7

----i (illl Mot

C

lt l -H uP =

I

I-

-LL

S m11 1 I I I IJG I

I

Out










(a)

+ 8V RtreclO1 Stull

I I

CGoAs

(b)




367 MHz 367l MHz

(c)



SAW Drive

Input

Address Buss


Output







xv SAW SENSORS




















1473



B SAM Imaging












I D T I D T













---I LaJL

gtlt-___ -

() 35 45

33

plusmn 55





4221 47 0 0






AT -ATshycutcut

q u a rtz q u a rtz

V- axis V-axis

(a)

y

X (b)

















1475

OC

--

17

1


V v v

A V I I V f

V

V - - --- --













Cor












ACKNOWLEDGMENT


REFERENCES









































1477













































































































































































































































































































90












B5 FREOUENCY (MHz

































1463

85

---+- -+-+-P r o g ro m m o Ie









MIT TI Hazelt ine












T o p W e i g h t s







-J I D T

P o rt I n p u t









o dBm




PORT 1 Sig n a l

R T 2 R efere n c e


l ithium n io b ate

PORT 1 I nput coded

(a)

PORT 3 Output

sil icon layer

Air g a p 2000 A

(b)






1 465


































_ _ _ _ _ _ _ _ _ _ _ _ _ _

-------

-----------

--------














(Compression) 1---1

r- - - - - - --J T Bi e e


l _ _ _ _ _ _ _


(a)

CEPSTR U M S TAGE

I I Impu lse in L


ON-LINE



(c)




1467









146H






C(T) = I I [log l s ( t) ) 1 2)W (5)


I D (wW == I S (wW (1 + 2(3 cos (WT) + 32) (6)










I Input --- I rfs I






Photodiode Arra

Diffracted Ligh _

-- -

LiN b03 Lens lOT

(a)

Photo-Detector

PORT 2 INPUT INPUT

LiN b 0 3 Beam

(b)














1469














































1471

7J7l7

----i (illl Mot

C

lt l -H uP =

I

I-

-LL

S m11 1 I I I IJG I

I

Out










(a)

+ 8V RtreclO1 Stull

I I

CGoAs

(b)




367 MHz 367l MHz

(c)



SAW Drive

Input

Address Buss


Output







xv SAW SENSORS




















1473



B SAM Imaging












I D T I D T













---I LaJL

gtlt-___ -

() 35 45

33

plusmn 55





4221 47 0 0






AT -ATshycutcut

q u a rtz q u a rtz

V- axis V-axis

(a)

y

X (b)

















1475

OC

--

17

1


V v v

A V I I V f

V

V - - --- --













Cor












ACKNOWLEDGMENT


REFERENCES









































1477


































































































































































































































































































































1463

85

---+- -+-+-P r o g ro m m o Ie









MIT TI Hazelt ine












T o p W e i g h t s







-J I D T

P o rt I n p u t









o dBm




PORT 1 Sig n a l

R T 2 R efere n c e


l ithium n io b ate

PORT 1 I nput coded

(a)

PORT 3 Output

sil icon layer

Air g a p 2000 A

(b)






1 465


































_ _ _ _ _ _ _ _ _ _ _ _ _ _

-------

-----------

--------














(Compression) 1---1

r- - - - - - --J T Bi e e


l _ _ _ _ _ _ _


(a)

CEPSTR U M S TAGE

I I Impu lse in L


ON-LINE



(c)




1467









146H






C(T) = I I [log l s ( t) ) 1 2)W (5)


I D (wW == I S (wW (1 + 2(3 cos (WT) + 32) (6)










I Input --- I rfs I






Photodiode Arra

Diffracted Ligh _

-- -

LiN b03 Lens lOT

(a)

Photo-Detector

PORT 2 INPUT INPUT

LiN b 0 3 Beam

(b)














1469














































1471

7J7l7

----i (illl Mot

C

lt l -H uP =

I

I-

-LL

S m11 1 I I I IJG I

I

Out










(a)

+ 8V RtreclO1 Stull

I I

CGoAs

(b)




367 MHz 367l MHz

(c)



SAW Drive

Input

Address Buss


Output







xv SAW SENSORS




















1473



B SAM Imaging












I D T I D T













---I LaJL

gtlt-___ -

() 35 45

33

plusmn 55





4221 47 0 0






AT -ATshycutcut

q u a rtz q u a rtz

V- axis V-axis

(a)

y

X (b)

















1475

OC

--

17

1


V v v

A V I I V f

V

V - - --- --













Cor












ACKNOWLEDGMENT


REFERENCES









































1477













































































































































































































































































































85

---+- -+-+-P r o g ro m m o Ie









MIT TI Hazelt ine












T o p W e i g h t s







-J I D T

P o rt I n p u t









o dBm




PORT 1 Sig n a l

R T 2 R efere n c e


l ithium n io b ate

PORT 1 I nput coded

(a)

PORT 3 Output

sil icon layer

Air g a p 2000 A

(b)






1 465


































_ _ _ _ _ _ _ _ _ _ _ _ _ _

-------

-----------

--------














(Compression) 1---1

r- - - - - - --J T Bi e e


l _ _ _ _ _ _ _


(a)

CEPSTR U M S TAGE

I I Impu lse in L


ON-LINE



(c)




1467









146H






C(T) = I I [log l s ( t) ) 1 2)W (5)


I D (wW == I S (wW (1 + 2(3 cos (WT) + 32) (6)










I Input --- I rfs I






Photodiode Arra

Diffracted Ligh _

-- -

LiN b03 Lens lOT

(a)

Photo-Detector

PORT 2 INPUT INPUT

LiN b 0 3 Beam

(b)














1469














































1471

7J7l7

----i (illl Mot

C

lt l -H uP =

I

I-

-LL

S m11 1 I I I IJG I

I

Out










(a)

+ 8V RtreclO1 Stull

I I

CGoAs

(b)




367 MHz 367l MHz

(c)



SAW Drive

Input

Address Buss


Output







xv SAW SENSORS




















1473



B SAM Imaging












I D T I D T













---I LaJL

gtlt-___ -

() 35 45

33

plusmn 55





4221 47 0 0






AT -ATshycutcut

q u a rtz q u a rtz

V- axis V-axis

(a)

y

X (b)

















1475

OC

--

17

1


V v v

A V I I V f

V

V - - --- --













Cor












ACKNOWLEDGMENT


REFERENCES









































1477















































































































































































































































































































-J I D T

P o rt I n p u t









o dBm




PORT 1 Sig n a l

R T 2 R efere n c e


l ithium n io b ate

PORT 1 I nput coded

(a)

PORT 3 Output

sil icon layer

Air g a p 2000 A

(b)






1 465


































_ _ _ _ _ _ _ _ _ _ _ _ _ _

-------

-----------

--------














(Compression) 1---1

r- - - - - - --J T Bi e e


l _ _ _ _ _ _ _


(a)

CEPSTR U M S TAGE

I I Impu lse in L


ON-LINE



(c)




1467









146H






C(T) = I I [log l s ( t) ) 1 2)W (5)


I D (wW == I S (wW (1 + 2(3 cos (WT) + 32) (6)










I Input --- I rfs I






Photodiode Arra

Diffracted Ligh _

-- -

LiN b03 Lens lOT

(a)

Photo-Detector

PORT 2 INPUT INPUT

LiN b 0 3 Beam

(b)














1469














































1471

7J7l7

----i (illl Mot

C

lt l -H uP =

I

I-

-LL

S m11 1 I I I IJG I

I

Out










(a)

+ 8V RtreclO1 Stull

I I

CGoAs

(b)




367 MHz 367l MHz

(c)



SAW Drive

Input

Address Buss


Output







xv SAW SENSORS




















1473



B SAM Imaging












I D T I D T













---I LaJL

gtlt-___ -

() 35 45

33

plusmn 55





4221 47 0 0






AT -ATshycutcut

q u a rtz q u a rtz

V- axis V-axis

(a)

y

X (b)

















1475

OC

--

17

1


V v v

A V I I V f

V

V - - --- --













Cor












ACKNOWLEDGMENT


REFERENCES









































1477













































































































































































































































































































Documents

Applications of surface acoustic and shallow bulk acoustic ...ieee-uffc.org/wp-content/uploads/2016/09/e89a1453.pdf · Extensive development of shallow bulk acoustic wave (SBAW) devices