Vco Based Fbar

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FACULTY OF ENGINEERING AND SUSTAINABLE DEVELOPMENT .

Design and Development of Gigahertz Range VCO Basedon Intrinsically Tunable Film Bulk Acoustic Resonator

Danial Tayari

June 2012

Masters Thesis in Electronics

Masters Program in Electronics/Telecommunications

Examiner: Prof. Daniel Rnnow

Supervisor: Prof. Spartak Gevorgian


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PREFACE

The Master s the sis is the outcome of my research at Terahertz and millimeter wave laboratory

of Chalmers University of Technology, Sweden, for the Master s program in Electronics/

Telecommunication Engineering at University of Gvle, Sweden.

Professor Spartak Gevorgian at Chalmers University of Technology supervised me during the thesis.

The thesis is examined by Professor Daniel Rnnow at University of Gvle.

The main focus of the thesis is on design and fabrication of voltage controlled oscillators by the

use of tunable film bulk acoustic resonator. The design was done in Advanced design system

(ADS) and fabrication was performed at Chalmers clean room at the department of Micro

technology and Nano Science, MC2.


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AbstractThe purpose of this thesis is to design and fabricate Gigahertz range voltage controlled oscillator based on intrinsically tunable film bulk acoustic resonator.

Modified Butterworth Van Dyke (MBVD) model was studied and implemented to simulateFBAR behavior. Advanced designed system (ADS) was used as the simulation tool.

Oscillator theory is studied and an oscillator based on non-tunable FBAR at 2GHz is simulatedwhich shows -132 dBc/Hz phase noise @ 100 kHz offset frequency.

A 5.5 GHz Voltage controlled oscillator based on intrinsically tunable FBAR is designed.Frequency tuning of 129 MHz with phase noise of -106 dBc/Hz @ 100 kHz is achieved. Thecircuit is designed on a novel carrier substrate which includes integrated resonators and passivecomponents. Bipolar junction transistors are mounted on the carrier substrate by silver epoxy.

The thesis describes the design, development and processing of the carrier substrate, BSTO based resonators, and the oscillator circuit.


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AcknowledgmentsI would like to thank Professor Spartak Gevorgian for considering me as a member of hisresearch group.His constant supervision during the thesis period guided me through the right

pass to achieve my goal.Dr.John Berge who helped me in the fabricat ion process of the VCO,without his help thefabrication wouldn t have been done in the proposed time.

My special thanks to Professor Daniel Rnnow for accepting to be the examiner of my work.

To my friends at Gvle and Gteborg who always helped and supported me during my stay inSweden.

Finally I am thankful to my family for encouraging and supporting me in life.


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Notations and Abbreviations

Notations

C Capacitance

Cm Motional capacitance

f off ,off Offset (angular) frequencyg Coplanar wave guide gap width

k t (effective) piezoelectric coupling coefficient

Phase-noise relative to carrier at offset frequency

Lm Motional inductance

PDC DC power

Q p Parallel resonance quality factor

Qs Series resonance quality factor

R m Motional resistance

s Coplanar wave guide strip width

Zo Characteristics impedance

eff Effective permittivity

Attenuation constant Acoustic phase


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Abbreviations

AC Alternating Current

AIN Aluminum Nitride

BAW Bulk Acoustic Resonator

BJT Bipolar Junction Transistor

BSTO Barium Strontium Titanate

CPW Coplanar Waveguide

DC Direct Current

FBAR Film Bulk Acoustic Resonator

FOM Figure of Merit

GSG Ground Signal Ground

HFO Hafnium Oxide

IF Intermediate Frequency

LO Local Oscillator

MBVD Modified Butterworth Van-Dyke

PLD Pulsed Laser Deposition

PN Phase Noise

RF Radio Frequency

SAW Surface Acoustic Wave

VCO Voltage Controlled Oscillator

ZnO Zinc Oxide


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Contents 1 Introduction ......... .......... ........... ......... .......... .......... ........ ........... .......... ......... .......... .......... 1

1.1 Introduction and Motivation.......................................................................................... 1

2 Film bulk acoustic resonators.......... .......... .......... ......... .......... ........... ........ .......... ........... .... 3

2.1 Characteristics ............................................................................................................. 6 2.1.1 Quality factor .......... .......... ........... ........ .......... ........... ........ ........... .......... ......... ..... 6

2.1.2 Effective Coupling coefficient........... .......... .......... ......... .......... ........... ........ ........... . 6

2.2 Modeling .................................................................................................................... 7

2.3 Tunable FBAR ............................................................................................................ 8

3 Oscillator theory .......... .......... .......... ......... .......... ........... ........ .......... ........... ........ ........... ..11

3.1 Types of oscillators ..................................................................................................... 11

3.1.1 Relaxation oscillators .......... ........... .......... ........ ........... .......... ......... .......... .......... ..11

3.1.2 Harmonic oscillators..... ........... .......... ......... .......... .......... ......... .......... ........... ........12

3.2 Oscillation criteria....................................................................................................... 12

3.2.1 Reflection oscillator ........... .......... .......... ......... .......... ........... ........ .......... ........... ...14

3.2.2 Transistor oscillator .......... .......... ........... ........ ........... .......... ......... .......... .......... .....15

3.3 Oscillator Phase noise.................................................................................................. 16

3.4 Oscillator figure of merit.............................................................................................. 17

4 FBAR Oscillators .......... ........... .......... ........ ........... .......... ......... .......... .......... ......... ........... 18

4.1 Fixed frequency FBAR Oscillator .................................................................................. 19

4.2 Voltage controlled oscillator (VCO) Based on Non-tunable FBARs.................................... 22

5 Tunable FBAR VCO .......... ........... .......... ......... .......... .......... ......... .......... .......... ......... ......25

5.1 Design....................................................................................................................... 25

5.1.1 ADS momentum design .......... ........... .......... ......... .......... .......... ......... ........... ........26

5.1.2 Substrate definition .......... .......... ........... ........ ........... .......... ......... .......... .......... .....26

5.1.3 Coplanar waveguide ........... .......... .......... ......... .......... ........... ........ .......... ........... ...27

5.1.4 Grounding capacitors.......... .......... .......... ......... .......... ........... ........ .......... ........... ...29

5.1.5 Tunable FBAR resonator.................. .......... ......... .......... ........... ........ .......... ...........315.1.6 Decoupling capacitor .......... .......... .......... ......... .......... ........... ........ .......... ........... ...32

5.1.7 Meandered circuit .......... ........... .......... ......... .......... .......... ......... .......... ........... ......33

5.1.8 Co-Simulation .......... ........... .......... ......... .......... .......... ......... .......... ........... ........ ...34

6 Device Fabrication and Measurement ........... .......... .......... ......... .......... ........... ........ ........... 37

6.1 BSTO film growth by the PLD...................................................................................... 38


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6.1.1 PLD overview .......... ........... .......... ......... .......... .......... ......... .......... ........... ........ ...38

6.1.2 Laser-target interaction. .......... ........... .......... ......... .......... .......... ......... ........... ........39

6.1.3 The plume.......... .......... .......... ......... .......... ........... ......... .......... .......... ......... .........39

6.1.4 Pulsed laser .......... .......... .......... ......... .......... ........... ........ .......... ........... ........ ........39

6.2 Measurements .......... .......... .......... ......... .......... ........... ......... .......... .......... ......... .........42

6.2.1 Test resonator measurement................... .......... ......... .......... ........... ........ ........... .....42

6.2.2 Oscillator measurements ......... ........... .......... ......... .......... .......... ......... .......... .........44

7 Conclusion and future work .......... .......... ........... ........ ........... .......... ......... .......... .......... .....45

8 References .......... ........... .......... ......... .......... .......... ......... .......... ........... ........ .......... ........... 46

Appendix1: Tunable FBAR Resonator MBVD model Extracted Parameters ...............................49

Appendix2: Transmission line parameter extraction ..................................................................50

Appendix3: Fabrication Steps and recipe .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... ..53


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1 Introduction

The motivation for the work presented in the thesis and thesis organization are provided in thischapter.

1.1 Introduction and Motivation

Oscillators are devices which create a periodic AC signal at a defined frequency. All RF andmicrowave devices containing transmitters or receivers use oscillators. Usually oscillators aredeployed in receivers and transmitters with mixers in which the signal can be up or downconverted in frequency. In contrast to fixed frequency oscillators, - the voltage control oscillators(VCOs) can produce a range of frequencies enabling the radio device using them to operate onmany different frequencies.

Communication systems frequency range can be determined by the frequency range of theoscillator. So this frequency range is desirable to be large enough for covering the operatingcommunication band.

In today s communication systems, staying within the allocated frequency band and notdisturbing other users of adjacent frequencies is very important. Therefore the frequency stabilityof the devices should be very high. In case of oscillators the frequency stability is defined by its phase noise and it is a critical issue since it determines the frequency stability of the complete

radio transceiver.There are number of parameters affecting the oscillator phase noise. One of the most importantone is the reactive components quality factors. In LC oscillators reactive components such asinductors and capacitors are employed in the resonator part .The LC resonator defines theoscillation frequency and the quality factor of the resonator has significant impact on oscillator phase noise. So the concern is to have resonators with higher quality factor. LC resonator qualityfactor is generally very low (around 20) making it a challenge for designers to design low phasenoise oscillators based on LC resonators. However designing broad frequency range oscillators iseasier when using these low quality factor components.

To have high quality resonators, surface acoustic wave (SAW) and bulk acoustic wave (BAW)devices can be used. The film bulk acoustic resonator (FBAR) is a type of recently developedBAW devices with very high quality factor.

The main focus of this thesis work is to present an oscillator based on quite recently developedtunable FBAR, based on BSTO material in which presents tunable characteristics under dc bias.


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These types of FBARs make it possible for the oscillator to have relatively high tuning rangecompared to traditional AlN FBAR oscillators and are suitable in wireless communicationsystems and sensor applications, e.g. bio sensing.

The contents of this thesis are organized as follows.

Chapter 2 discusses the film bulk acoustic resonator, its characteristics and modeling. TunableFBARs are also briefly introduced in this chapter. Chapter 3 gives some background onoscillation theory and important criteria for oscillators. Design of fixed frequency FBARoscillators is presented in chapter 4 while chapter 5 gives detailed explanation of a VCO basedon tunable FBAR. Chapter 6 argues about the fabrication process and presents the measurementresults. The conclusions and future work are given in the final chapter.


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2 Film bulk acoustic resonators

Film bulk acoustic resonator (FBAR) consists of a piezoelectric thin film which is sandwiched by a pair of electrodes. Depending on the applied frequency of the e lectrical signal to the FBAR;

its piezoelectric material may expand or contract resulting in generation of the acoustic waves.When the thickness of the piezoelectric layer is the same as an integer of half acousticwavelength the resonance occurs which means the resonance frequencies are determined bythickness and are independent from lateral dimensions.

At some frequency the impedance of FBAR reaches its minimum magnitude, which means thegenerated acoustic wave travels in the most efficient way through the physical material. Thisfrequency is referred to the series resonant frequency f s . On the other hand when FBARimpedance magnitude reaches its maximum there is no response from the piezoelectric meaningthat no acoustic wave transfers energy through the FBAR. This happens at parallel resonancefrequency or anti resonance frequency f p[1].

Fig. 2.1 FBAR structure under bias volt age

Piezo-electric material


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Fig. 2.2 illustrates the relation between the FBAR Impedance and its resonance frequencies

In comparison to LC resonators FBAR offers very high quality factor. In recent years FBARsusing different material with very high quality factors of more than 2000 at a few gigahertzeshave been introduced and FBAR duplexer filters for mobile phones now are commercially inuse. Integrated LC resonators with varactor typically have Q factor of around 20.

In order to have high quality factor of the FBAR, the resonator must be acoustically isolatedfrom the substrate. Depending on the Type of isolation FBARs are categorized as solidlymounted or membrane mounted, Fig. 2.3.

The first type uses an acoustic reflector, a Bragg reflector, consisting of /4 layers with high andlow acoustic impedance alternatively. The second type based on an air cavity formed below the bottom electrode.

Series resonance

Parallel resonance

Fig. 2.2 A typical FBAR frequency response. Parallel and series resonances are shown


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(a) (b)

Fig 2.3(a) solidly mounted and (b)membrane mount ed FBAR

Dimensions of FBAR are relative to acoustic wavelength. Acoustic propagation speed in solidmaterials is about 103 _104 m/s. For electromagnetic waves however it is of order 107 _108 m/s. Soacoustic wavelength is four to five order of the magnitude lower than electrical wavelength,consequently FBARs are much smaller than electromagnetic resonators based on transmissionline segments, for example. In addition acoustic loss is fairly low for piezoelectric materials atgigahertz range making them useful for high quality factor resonators at those frequencies. Forexample AlN_FBARs with quality factor of 280 demonstrated at 20 GHz at [2]. Some reportedFBARs are given in Table 2.1.

Table 2.1: some recently reported FBARS

Reference f s[GHz] Qs Size[mm ]

[3] 1.1 386 0.058

[4] 1.9 832 -

[5] 1.9 1200 0.01

[6] 5 290 -

[7] 1.9 1025 -

[8] 4.9 300 -

[9] 1.8 8000 -

Air

Top-electrode


Silicon

bottom-electrode

Top-electrode


Silicon

bottom-electrode

Z1

Z2

Z2

Z1


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2.1 Characteristics

The important characteristics of FBAR relevant for Oscillators are the Q-factor (quality factor)and the resonance frequencies. Regarding these, the coupling coefficient is important in that the

quality factors and impedance response depend on it.

2.1.1 Quality factor

For a resonator the quality factor is defined as

(2.1)

Where the maximum Energy stored in the resonator and is the energy dissipated inthe lossy sections in one resonance period.In simple resonators Q is commonly obtained from 3_dB bandwidth of the impedance. InFBARs however, the Q can be determined by the equation given in [10].

| | (2.2)2.1.2 Effective Coupling coefficient

The coupling coefficient shows the percentage of the energy converted from mechanical toelectrical and vice versa. [11]

(2.3)


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2.2 Modeling

One of the most commonly used models for FBAR is the modified Butterworth-Van Dyke(MBVD) model. [12] Which is shown in Fig. 2.4

Rm Cm Lm

Rs

R0 C0

Fig. 2.4 MBVD model

In this model C0 represents the parallel plate capacitance, Cm, Lm, and R m show the acoustic

resonance, R s represents the ohmic loss of the electrodes while R 0 defines the dielectric loss.Typically the MBVD model is extracted from the measurements and used as a model in circuitsimulation.

The measured reflection coefficient of an FBAR resonator and its equivalent MBVD model is plotted in Fig. 2.5. The parameters of MBVD model should be tuned in a way that simulated andmeasured plots fit each other excellently.

Fig. 2.5 measured and equivalent MBVD model reflection coefficient


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2.3 Tunable FBAR

Traditional FBARs are not tunable, however in case of intrinsically tunable FBAR a DC voltageis used to tune the resonance frequency of FBAR [13]. A tunable FBAR can be obtained from

the DC field dependency of dielectric constant, acoustic velocity and electromechanical couplingcoefficient

As an example of tunable FBAR, presented in [14] is shown in Fig. 2.6(a). For this FBAR,BSTO as the ferroelectric material and HfO2 and SiO2 as the layers of the Bragg reflector areused.

As the bias voltage increases the resonance loop grows. For comparison Fig. 2.6(b) represent a plot of traditional FBAR. Although the resonance frequencies are not the same, we can see thedifference between these two. For a given resonance frequency and capacitance, the resonanceloop size is governed by the effective coupling coefficient and acoustic quality factor.This shows that FBAR Based on AlN gives much higher quality factor than the BSTO tunableone.

Table 2.2 gives the resonance frequencies of the resonator for different bias voltages. Theresonator is then connected to the rest of the circuit.

(a) (b)Fig. 2 .6 (a) Tunable FBAR resonat ing from 5.5GHz to 5.7 GHz (b)ALN non tunable FBAR resonat ing at 2 GHz


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Table 2.2: Extracted resonance frequencies from resonator MBVD model

Bias voltage(V) f s(GHz) f p(GHz)

5 5.729 5.752

10 5.658 5.74315 5.612 5.722

20 5.58 5.733

25 5.553 5.712

Extracted parameters of the MBVD model are given in Figure 2.7.

(a)

Motional Inductance vs. DC Bias

0

2

4

6

8

10

12

0 5 10 15 20 25 30

Voltage(V)

M o t

i o n a

l I n d u c

t a n c e ( n H

)


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(b)

(c) Fig. 2.7 Ext racted MBVD model parameters vs. bias voltage (a) mot ional inductance Lm (b) motional resistance R m (c) motional

and static capacitance Cm and C0

Motional Resistance vs. DC Bias

1.51.61.71.81.9

22.12.22.32.42.5

0 5 10 15 20 25 30

Voltage(V)

M o t

i o n a

l R e s

i s t a n c e (

O h m s )

Motional & Static capacitance vs. DC Bias

0

1

2

3

4

56

0 5 10 15 20 25 30

Voltage(V)

C 0 ( p F

)

020406080100120140160

C m

( f F )

C0(pF)

Cm(fF)


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3 Oscillator theory

An oscillator is a circuit which uses DC power to generate periodic AC signal at its output. In anoscillator there is no need for any input signal except for the DC power supply. This chapter

discusses briefly the two main types of oscillators, criteria to have the oscillation and theimportant merits to evaluate the oscillator performance. More explanations about working principle of the oscillators can be found in [15].

3.1 Types of oscillators

Oscillators are divided into two main groups, relaxation oscillators and harmonic Oscillators.

3.1.1 Relaxation oscillators

These oscillators switch repetitively between two states e.g. charging or discharging a capacitoror inductor. The amplitude of the charging current and the time constant determines thefrequency of oscillation.

A simple relaxation oscillator is shown in Fig. 3.1

Fig. 3.1 Schematic of a relaxation oscillator [15]


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3.1.2 Harmonic oscillators

A harmonic oscillator consists of a resonator and an active device. The active device cancels thelosses in the resonator, resulting constant oscillation amplitude at the frequency defined by the

resonator.In the oscillators the resonator is made of an inductor and a capacitor. The resonancefrequency of a circuit is dependent on the values of the inductor and capacitor and defined as

Where is the value of the inductor and is the value of the capacitor.For microwave frequencies, harmonic oscillators are preferred due to better phase noise

performance. The oscillators in this work are of harmonic type.

3.2 Oscillation criteria

Harmonic oscillators use positive feedback. If a transistor is sufficiently biased it can provideenough feedback from the output for oscillation. This type of design is known as reflectionoscillation which is explained later in this chapter. A schematic of a feedback oscillator is shownin Fig. 3.2

An amplifier is shown by block while represents feedback block connecting output to theinput. A small input signal is used to understand the oscillation.

Fig. 3.2 feedback oscillator schemat ic


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The output signal is having a transfer function given in (3.2)

(3.2)Where is the forward gain and a function of the amplitude of the signal, while dependence of

the feedback , is typically on the signal frequency .The open-loop gain is identified as

(3.3)Analyzing small-signal closed loop transfer function can be done to see if the circuit hasnecessary condition for oscillation. It is important that the function has a pair of poles in theright hand plane (RHP), or

Number of poles in theRHP + Number of poles inLHP > 0

Identifying the c losed-loop transfer function and its poles is usually a difficult task. Instead small

signal open-loop gain can be analyzed. To do this in simulation one can break open thecircuit appropriately for open loop analyses.

The Nyquist criterion represents an oscillation criterion which is based on the open-loop gain analyses. According to this criterion when the small signal loop gain encircles the point 1+j0 inthe clock wise direction with increasing frequency, the closed-loop system is unstable.

An example of the Nyquist plot is shown in Fig. 3.3

Fig. 3.3 (a)Nyquist plot for a circuit showing instability (b) Magnitude and phase of the open loop gain


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The oscillation is guaranteed by Nyquist criterion, but since this criterion is based on the small-signal loop gains, no information regarding steady state frequency and amplitudeoscillation can be obtained from it.

To have stable oscillation, loop gain must decrease and eventually be equal to 1+j0.This is

known as Barkhusen criterion [16]In practice after the oscillation has been started the magnitude of the loop gain, due to the devicenon-linearity will be reduced to 1 for stable amplitude.

Having a zero phase in the loop gain means all the signals are summed together, producing a sumthat is greater than any of the single signals. If they were in opposite phase for example, theywould have cancelled out, resulting in no oscillation.

3.2.1 Reflection oscillator

Reflection oscillators are common topology for microwave oscillators since the necessaryfeedback to make the circuit unstable can be provided by parasitic elements of the amplifier.

Fig. 3.4 shows RF-circuit for one port negative-resistance oscillator.

0+ +

0+

0+ +

0+

Fig.3.4 one port negative-resistance oscillator


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Where Zin = R in+ jXin is the input impedance of the active device and ZL = R L+ jXL is theimpedance of the passive load.

For the oscillation to occur the following conditions must be satisfied:

+

+ For a passive load , indicating . So the negative resistance refers to an energysource. When the magnitude of the signal which causes the negative resistance and the loss ofthe passive component (resonator) are balanced, steady state oscillation happens.

3.2.2 Transistor oscillator

In this type of oscillator the negative resistance is provided by terminating a potentially unstabletransistor. The circuit model is shown in Fig. 3.5.

Negative resistance

TransistorTerminating

Network

Load

Network

Fig. 3.5 Oscillator circuit model of negative resistance topology


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3.3 Oscillator Phase noise

Phase noise is an important parameter for performance of an oscillator and is a way to qualifyfrequency stability. Short term random fluctuations in the output signal are referred as phase

noise. For a given signal as

0+ both the amplitude and phase are constant but in realistic oscillators either external orinternal noise-sources to the oscillator cause both quantities to have fluctuations.

Output spectrum of a realistic oscillator is given in Fig. 3.6

Amplitude variation is limited and due to circuit non-linearities for steady state oscillation hasless impact on the oscillator performance. Phase variation on the other hand may be random anddiscrete- making it the main contributor in oscillation-noise.

In communication systems it is important for devices to stay in their defined operating frequency band, thus phase noise plays an important role s ince the frequency stability of the total system is

Random phase variations

Discrete spurious signals

frequencyf 0

Amplitude

Fig. 3.6 Output spectrum of RF oscillator


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determined by the frequency stability of the oscillator. For instance a local oscillator may causechannel interference due to its high phase noise when used in a down converter as shown in

Fig. 3.7.

Power

Frequency

Oscillator phase noise is defined as the ratio of the power of a side band to the power of thecarrier frequency at an offset frequency from the carrier. Typically the side band isnormalized by the unit bandwidth.

( )( ) 0 3.4 Oscillator figure of merit

Figure of merit (FOM) is used to rank oscillators. The most common FOM is given by (3.8)

+ (3.8)Where is the phase noise in dBc/Hz , is the offset frequency , 0 is the oscillationfrequency and PDC is the transistor DC power consumption in milliwatt.

Interference wanted and adjacent channels

f IF f LO

Fig. 3.7 channel interference caused by noisy local oscillator


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4 FBAR Oscillators

The small size and high quality factor of FBAR resonators make them to be of interest inmicrowave oscillators.

Table 4.1 shows some publications of Oscillators based on FBAR.

Table 4.1: Summary of FBAR.based Oscillators

year Ref FBAR Resonatorintegration

Technology f 0

[GHz]

Pout

[dBm]

PDC

[mW]

PN

[dBc/Hz]

FOM

[dB]

1984 [17] ZnO,mm Mounted on pcb

0.259 -24 -66@100 kHz

2001 [18] ZnO,mm Mounted on

pcb

AlGaAS

HBT

2.2 -108@100kHz

2003 [19] AlN,mm Mounted on pcb

bipolar 1.985 10 -11 2@ 10 kHz 197

2005 [20] ZnO,mm Mounted on pcb

1.1 -13.6 -115@ 10 kHz

2008 [21] sm Mounted on pcb

130 nmCMOS

2.2 6 -136@1 MHz 195

2008 [22] ALN,sm Mounted on pcb

65 nm CMOS 2 0.06 -124@100kHz 222

2008 [23] sm Mounted on pcb

65 nm CMOS 2 0.9 -128@100kHz 214

2009 [24] ALN,sm Mounted on pcb

BiCMOS 2.11 21.6 -136@100 kHz 209

2011 [25] ALN,mm Mounted on pcb

0.18 mCMOS

2 0.022 -121@100kHz 222.9

1mm=membrane mounted, sm=solidly mounted

2simulated


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4.1 Fixed frequency FBAR Oscillator

The topology used in this work to design a fixed frequency FBAR oscillator is shown in Fig. 4.1.A commercial BJT transistor (Infineon BFP-420) on common-base topology is used and the

circuit is designed as negative resistance Oscillator so that the transistor parasitic providesnecessary feedback required.

ZR Za

Fig.4.1 common base topo logy

For the circuit to oscillate the oscillation condition ZR +Za=0 must be satisfied. This can beachieved by designing a proper output matching network.The resonator is placed at the emitter port via a matching network. The resonator implemented in the c ircuit is of AlN solidly mountedtype presented in [26].

The equivalent MBVD model of the resonator is given in Fig 4.2, while Table 4.2 summarizes

corresponding parameters, - the series and parallel resonance frequencies, as well as the Qfactors.

Rm Cm Lm

Rs

R0 C0

Fig. 4.2 2 GHz FBAR MBVD model

Table 4.2: 2 GHz FBAR extracted parameters [26]

R m= 1.4 Cm=72.2 fF Lm=83.9 nH R s=2.8 R 0=0.5 C0=3.7 pF

f s=2.045 GHz f p=2.065 GHz Qs=750 Q p=250

Resonator output

matchingnetwork

Resonatormatchingnetwork


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As it is discussed in chapter 2 FBAR shows much lower impedance at the series resonance thanof the parallel one making it easier to design the matching network for compensating the lossesof the resonator. Regarding this the Oscillator is designed functioning at the series resonance ofthe resonator. The circuit is based on 0.6 mm Alumina substrate and microstrip transmissionlines are used as matching networks.

Simulation is done using Agilent ADS software. Large signal model provided by themanufacturer is used to characterize the transistor, which is biased at Vcc=4 V and Ic=20 mA Theoutput matching is designed to create an impedance which cancels out the resonator losses sothere is no need for extra matching network at the resonator side.

Quarterwave transmission lines and capacitors are used as RF chokes, Harmonic balance is usedfor large signal analysis of the steady state oscillation and finally the procedure is completed byfine tuning the circuit. Fig. 4.3 shows the ADS schematic of the circuit.

Fig. 4.3 ADS schematic o f t he designed 2 GHz fixed frequency FBAR Oscillator

Fig. 4.4(a) shows the output spectrum of the circuit. It can be seen that the circuit oscillates at2.044 GHz which agrees with the resonator series resonance frequency.

The Oscillator phase noise is given in Fig. 4.4(b). At 100 kHz offset from the fundamental, theoscillator has a phase noise of -132 dBc/Hz which is better than the one reported in[22].

The output waveform is given Fig. 4.3(c) in two periods.

FBAR model


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Fig. 4.3 2 GHZ FBAR Oscillator (a) output spectrum (b)phase noise plot

(c) output volt age in time domain

(a) (b)

(c)


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4.2 Voltage controlled oscillator (VCO) Based on Non-tunable FBARs.

In LC oscillators frequency tuning can usually be achieved by directly connecting a controlvoltage at the varactor part of the resonator. In AlN FBAR oscillators however this method

doesn t give frequency tuning range higher than 1 MHz. Some of the reported VCOs based onnon-tunable FBAR are listed in Table 4.3.

Table 4.3: comparisons of non-tunable FBAR VCOs

Reference f 0(GHz) Power Tuningrange[MHz]

BestPN@1MHz[dBc/Hz]

FOM[dB] Technology

[20] 1.1 - 0.2 -123 - Discrete

[19] 2 3.3V/35

mA

2.5 -150 -195 Bipolar

[27] 2.1 2.4V/24.3mA

37 -144 -193 0.25mBiCMOS+aboveIC

[28] 2 67w 10 -149 -220 0.13mCMOS

Fig. 4.4 shows a colpitts based PCB oscillator, with the FBAR wire bonded to the circuit. Thistopology is used in [20] and by applying a DC control voltage a very small frequency tuningrange is achieved.

Vtune Vdd

FBAR

Fig. 4.4.Colpitts based Oscillator [20]


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The VCO in [19] is based on common-collector topology. The FBAR is wire bonded to theOscillator and a varactor is coupled to the FBAR to reach the tunability of 2.5 MHz at 2 GHz.

Fig. 4.5 FBAR VCO with tuning varactor [19]

The circuit diagrams in [27] and [28] are given Fig. 4.6 and Fig. 4.7.

Fig. 4.6 circuit diagram of the series resonance FBAR VCO core with a single ended output buffer [27]


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The parasitic, non-tunable, reactive elements of the circuit always reduce the frequencytunability. By comparing the works that have been done until now it can be understood that tohave more tuning range of the FBAR the circuit topology gets more complicated and yet thetuning range is quite low compared to LC VCOs.

Due to limitations in fabrication process, in this work the purpose was to design a high tuningrange FBAR VCO keeping the circuit topology as simple as possible by using only onetransistor. Chapter 5 discusses the design of a voltage control oscillator based on intrinsicallytunable FBARs.

Fig. 4.7 FBAR-based differential Colpitts oscillator with gate-to-source feedback gain boosting [28]


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5 Tunable FBAR VCO

As it is mentioned in section [2.3] tuning of an FBAR is possible by having ferroelectric materiallike BSTO as the piezoelectric of the FBAR resonator. Oscillators based on tunable FBARs are

not studied previously and this work presents VCOs using tunable FBARS for the first time.

5.1 Design

In this section an integrated VCO based on Tunable FBAR is presented. The design andsimulation are done in Agilent ADS software and the final mask is prepared for fabrication process.

A single transistor topology is chosen in order to reduce the fabrication complexity. The tunableFBAR is located on the emitter of the transistor as shown in Fig. 5.1. The oscillator frequency isdefined by the series resonance frequency of the device which is tunable according to the applied bias voltage VR through the inductor L.

Fig. 5.1 Tunable FBAR Oscillator circuit Schemat ics

Decoupling capacitor C1 is used to isolate the resonator from the circuit in DC. An open stubmatching network at the output and inductive stub at the resonator ports make the compensation

for the resonator loss. Stubs S1 and S2 are quarter waves and AC shorted by capacitors C2 andC3The output is taken from the collector by a 50 load. Coplanar wave guide which.is used forthe stubs and matching network and the transistor is the same as in section [4.1] (base, twoemitters and collector).One of the emitters connects to the FBAR via S3 and the other is used fordc-bias through stub S1.

S3 Output

S1 S2

C1TFBAR

VR

L

VEE Vcc C3C2


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5.1.1 ADS momentum design

To do electromagnetic simulation of the circuit, the design is done in ADS momentum.

Each part of the circuit is separately simulated and finally Co-simulation is done to analyze thetotal circuit including DC analyses. The following section describes the design in momentum.

5.1.2 Substrate definition

The substrate used in this work was presented in [14] to achieve a tunable FBAR. Fig. 5.2 showsthe substrate layers with the corresponding thicknesses. The circuit is designed using 0.5mthick gold layer on top of the BSTO layer. For the resonator and circuit fabrication the metal

layers are patterned according the design as explained in sections [5.1.5-5.1.8].

Fig.5.2 Schematic view of the substrate cross section[14]

Ti/Al 10/100nm

Ba0.25Sr 0.75TiO2 234nm

Silicon

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Ti/Tio2/Pt 20/25/100nm


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5.1.3 Coplanar waveguide

The conventional coplanar waveguide (CPW) consists of conductors on top of a dielectric surface[29]. The two ground planes are separated from the center strip by the gap as shown in Fig. 5.3.

W

The thickness and permittivity of the substrate, the dimensions of the center strip and the gapwidth determine the characteristic impedance (Z0), the attenuation constant and the effectivedielectric constant (eff ) of the CPW. [29].Using CPW simplifies the fabrication, eliminates the need for via holes and reduces radiationloss [30]. In CPW characteristic impedance is determined not only by the strip but also the slotwidth, making possible to reduce the size without limit. The only drawback is higher losses[31].

To make low Z0 in conventional CPW, a very wide center strip conductor and a very narrow slotwidth can be fabricated. This however shows high current density at the slot edges whichincreases conductor losses; moreover a wide strip conductor can potentially couple power fromthe dominant CPW mode to unwanted spurious propagation modes. Therefore it is notrecommended to have conventional CPW lines with Z0 less than 30 [29].Fig. 5.3 shows the CPW used in this circuit design in ADS momentum.

Fig. 5.3 CPW line

Sg


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Fig. 5.3 CPW in ADS momentum

In this design, GSG ports are defined. Ports1 and 2 are defined as signal ports, ports 3 and 5 areground reference ports associated with port 1 and ports 4 and 6 are ground reference associatedwith port 2.Table 5.1 gives the line parameters extracted from the software by keeping the centerstrip width constant.

Table 5.1: Extracted CPW parameters from ADS moment um at 5.421 GHz

Z0( ) eff (dB/mm) g(m) S(m)

41.677 8.216 0.146 5 100

47 7.422 0.101 25 100

48.85 7.273 0.091 35 100

49.4 7.217 0.087 40 100

49.8 7.169 0.083 45 100

50 7.144 0.081 48 100

51.7 7.095 0.078 55 100

53 7.037 0.073 65 100

54.1 6.99 0.069 75 100


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It can be seen that the strip and gap widths of 100 and 48 m respectively, determined the CPWcharacteristic impedance of the 50 which was later used in the circuit design.

Using this data in the general transmission line model, the Oscillator circuit was designed basedon the measured data of the tunable FBAR resonator introduced in [14].

The ADS schematic of the circuit is shown in Fig. 5.4.

Fig. 5.4 ADS schematic of designed tunable FBAR VCO circuit

Due to the relatively low Q factor of tunable FBAR resonator it was decided to integrate thecircuit to reduce the noise caused by parasitic effects as much as possible.

5.1.4 Grounding capacitors

In order to AC ground the quaterwave stubs in the design, the platinum layer forms bottomelectrode of the capacitor. As shown in Fig. 5.5.

Since there are conductive holes in BSTO a 100 nm silicon dioxide layer is considered over theBSTO layer to isolate the top and bottom electrode in DC.

Tunable FBAR S1P model


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5.1.5 Tunable FBAR resonator

The resonator was modeled and designed according to the measured data obtained in [14]. Theresonator is connected to the emitter by an integrated inductor made from the Al top electrode.

The active area of the resonator is 700m2 Fig. 5.7 gives illustration of the resonator in

Momentum.

Fig. 5.7 Tunable FBAR resonator in ADS momentum

The geometry of the top-electrode in the active area is designed in way to suppress spuriouslateral acoustic resonances. The DC probe will be applied to the gold patch on the top ofaluminum inductor.To get the resonance frequency of the resonator Co-simulation is done byadding the motional parameters from MBVD model as shown in Fig. 5.8.

Resonatoractive area

ResonatorDC Biaslocation

MBVD modelmotional parameters

Spiral inductormade from TopAl electrode

Fig. 5.8 Tunable FBAR Co-simulation in ADS

Au

Al

Pt


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5.1.6 Decoupling capacitor

To isolate the DC bias of the resonator from other part of the circuit a series decoupling capacitornear the emitter leg is used, as shown in Fig. 5.9. Here again the gold layer and bottom electrode

are isolated using silicon dioxide layer.

Fig. 5.9 Decoupling capacitor (C1 and C2 form a series capacitor lett ing through t he RF and isolating DC of the resonator).

Capacitors C1 and C2 are formed between the platinum and gold layers with BSTO and SiO2 asThe dielectric material. The series capacitor is large enough not to load the resonatorto affect the RF signal and the discontinuity at the gold layer prevents the DC bias signaldisturbing the rest parts of the circuit. The decoupling capacitor is illustrated in Fig. 5.10 whichshows the total designed circuit in momentum

Fig. 5.10 T otal oscillator circuit in momentum

Transistor s Emitter

legResonator

RF signalPath

Pt

C1 BSTO C2

Au AuSio2


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5.1.7 Meandered circuit

Due to limitation in the fabrication and dimension of the sample (110mm) it was decided tomake the circuit as compact as possible so the transmission lines were meander in order to have

two circuits in one sample. The circuits with meandered lines are represented in Fig. 5.11

Fig. 5.11 meandered circuit


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5.1.8 Co-Simulation

Some modificat ion such as placing the resonators in the middle of the mask and adding some testresonators needed to be done for the final mask to get the optimum layout for fabrication. To see

the oscillator performance Co-simulation is done which is shown in Fig. 5.12

Fig. 5.12 Co-simulation of final oscillator design


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(c)

Co-simulation results for different bias voltages are given in Table 5.2.

Table 5.2: Oscillator Co-simulation results

Resonator bias volt age(V) Oscillation frequency(GHz) PN@100kHz(dBc/Hz)

5 5.655 -101

10 5.596 -106

15 5.561 -106.3

20 5.545 -106.3

25 5.526 -106.4

Fig. 5.13 Co-simulation results of tunable FBAR Oscillator (a)o utput volt age (b)phase noise (c) outputspectrum

(a) (b)

P o u

t ( d B m

)


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The Co-simulation results show that the Oscillation frequency tunability range of 129 MHz. Theoscillation frequency is slightly lower than the resonator series resonance frequency which isexpected for the loaded resonator. The phase noise is -106 dBc/Hz @ 100kHz frequency offsetfrom the carrier. The final mask for fabrication is given in figure 5.14

Fig. 5.14 final oscillator mask with the frame and alignment

Fig. 5.14 Final mask


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6 Device Fabrication and Measurement

Fabrication of the device is done at Chalmers Cleanroom. A 20 nm thick layer of TiO2 for betteradhesion between SiO2 and Pt using magnetron sputtering . The device layer is sputtered on the

1 1cm sample containing the Bragg reflector. Bottom electrode pattern has been mapped fromthe mask to the platinum bottom electrode by photolithography as shown in Fig. 6.1

Fig. 6.1 fabricated sample picture after bottom electrode pattering (the white areas show the platinum layer)


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6.1 BSTO film growth by the PLD

The growth of the BSTO film has been performed using Pulsed Laser Deposition .(PLD) andexplained in following section.

6.1.1 PLD overview

PLD concept is basically simple and is shown in Fig. 6.2.

Fig. 6.2 Schematic of PLD device [32]

A short pulsed laser beam is focused onto a target (BSTO in this work). Plasma is formedimmediately on the target surface due to the pulse energy. The plasma then reaches the substratewhich had been mounted on a heater and heated to the defined temperature and causes the targetmaterial to be deposited on the substrate.

There are numbers of parameters playing role in the deposited film quality. Some of those aregiven in the following sections.


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6.1.2 Laser-target interaction.

When the laser beam strikethrough the target surface, the material ablates out with samestoichiometry as in the target. The vapor pressure, absorption of the material and pulse laser

wavelength determines the amount of ablated material [33].

6.1.3 The plume

The target forms a plume after ablation. This high energy plume tends to move towards thesubstrate and presents forward peaking phenomenon [34].

Oxygen is often introduced into the chamber to keep constant the stoichiometry of the oxidematerial and reduce the kinetic energy [33].

The pressure of the background gas and the distance between the substrate and target define theshape of the plume.

6.1.4 Pulsed laserThe laser energy significantly affects the film quality. Higher energy increases the vapor pressureand consequently the kinetic energy which could result in defects in the surface of the depositedfilm due to re-sputtering.

Substrate temperature dramatically effects the deposited film quality in a way that highertemperature results in better quality.

Table 6.1 summarizes the process parameters used by PLD system in BSTO film deposition.

Table 6.1: PLD system Setting

parameters commentsLaser source KrFLaser wavelength 248 nmEnergy density 1.5 J.cm-Target BSTOOxygen pressure 20 PaRepetition rate 10 HzSubstrate Si/Hfo2/Sio2/./Tio 2/Pt

Substrate temperature 620 -640o CSubstrate-target distance 6 cm


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Fig. 6.3 shows the sample after BSTO deposition

Fig. 6 .3. 10 10 mm sample after BSTO deposition. The rain blow color shows the thickness difference of BSTO surface

Isolating SiO2, 100 nm aluminum top electrode and finally 500 nm gold layers were sputteredand patterned on the sample. A step by step fabrication process is presented in Appendix 3.TheAFM picture of the BSTO film in the middle of the sample is shown in Fig. 6.4.

Fig. 6.4.AFM picture of the BSTO film (a) 2D (b) 3D view of the BSTO film surface

The sample is shown in Figs. 6.5 (a), (b) and (c) after pattering of each layer.


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Fig. 6.5 fabricated sample aft er (a) Sio2 deposition & lift-off (b) Gold deposition & image reversal resist removal

(c) Al deposition & lift-off

(a) (b)

(c)


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6.2 Measurements

6.2.1 Test resonator measurement

Test resonator one port measurement was done using Agilent PNA N5230A and probe stationwith 150- m GSG mounted microprobes. Figures 6.7, 6.8 and 6.9 show the fabricated testresonator and measurement results.

Fig. 6.8 Test resonator reflection coefficient @ different DC bias voltages

Fig. 6.7 fabricated and measured Test resonator

2v5v

10v15v20v

DC Bias

G S G


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The test resonator measured results in comparison to the previously measured data which wasused in the oscillator circuit design show a shift of around 200 MHz downwards in the resonancefrequencies. It was also observed that maximum bias voltage for the resonator before the breakdown is 20V.These effects are due to the integrated inductor and fabrication processtechnology which differs slightly from the previously used resonator.

Fig. 6.9 measured series and parallel resonance frequencies

Test resonator series and parallel resonace frequencies

5.25.25

5.35.35

5.45.45

5.55.55

5.65.65

5.7

0 5 10 15 20 25

Voltage(V)

f s & f p ( G H z )

fp

fs

f sf p


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6.2.2 Oscillator measurements

To measure the oscillator, BJT transistors were mounted on the circuit by silver epoxy as shownin Fig. 6.10.

Fig. 6.10 Final oscillator circuits including transisto rs

Prior to RF measurement of the oscillator output spectrum and the phase noise, a DCmeasurement was done to verify the transistor is consuming the expected power as considered inthe simulation.

DC measurement showed that unfortunately the grounding capacitors were shorted to ground inDC due to the pin holes in SiO2 layer. That could be because of FHR device which heats thesample to several hundred degrees resulting a low quality SiO2 sputtered layer.


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7 Conclusion and future work

BSTO intrinsically tunable FBAR and passive components have been monolithically integratedon high resistivity silicon substrate. To demonstrate the optional of the technology, 5.5 GHz

voltage controlled Oscillator have been designed and fabricated on the substrate.

The simulated results showed high tunability with low phase noise compared to LC tankoscillators.

Measured Test resonators represent tenability of 114MHz @ 5.5 GHz. DC measurement of theOscillator revealed short circuit in the integrated RF grounding capacitors due to pin holes in theSiO2 and BSTO layer.

Future work will contain another fabrication round to prevent the pin holes by using E-beamevaporation technology for SiO2 deposition. Depending on the Oscillator performance, thefabrication process can be further optimized.

Oscillator circuit topology can be modified to improve the performance based on themeasurements of the latest presented tunable FBAR technology with higher Q factors.


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8 References

[1] R. Lanz and P. Muralt, Bandpass filters for 8 GHz usi ng solidly mounted bulk acousticwave resonators., IEEE transactions on ultrasonics, ferroelectrics, and f requency control , vol.

52, Jun. 2005, pp. 936-46.

[2] Y. Yoshino, Piezoelectric thin films and their applications for electronics, J. Appl. Phys. ,vol. 105, no. 6, pp. 061623-7, Mar. 2009.

[3] M. Ylilammi, J. Ell, M.Partanen, and J. Kaitila,Thin Film Bulk Acoustic Wave Filter, in IEEE Transactions an Ultrasonics, Ferroelectrics, and Frequency Control, vol. 49, no.4,Apr.2002,pp.535-539.

[4] S.-H. Lee, J.-H. Kim, G.D. Mansfeld, K.H. Yoon, and J.-K. Lee, Influence of Electrodes andBragg Reflector on the Quality of Thin Film bulk Acoustic wave Resonators, in IEEE

International Frequency Control Symposium and PDA Exhibition , 2002, pp. 45-49.

[5] B.P. Otis and J.M: Rabaey, A 300 - W 1.9-GHz CMOS Oscillator Utilizing MicromachinedResonators, in IEEE J. Solid-State Circuits , vol. 38,no. 7, July 2003,pp. 1271-1274.

[6] T. Yokoyama, T. Nishihara, S. Taniguchi, M. Iwaki, Y. Satoh, M. Ueda, and T.Miyashita,New Electrode Material for low -loss and High-Q FBAR Filters, in Proc. IEEE 2004Ultrasonics symposium , vol. 1, pp. 429-432.

[7] B. Ha, I. Song, Y. Park, D. kim, W. kim, K. Nam, and J.J. Pak, Novel 1 -chip FBAR Filterfor Wireless Handsets, in Int. Conf. On Solid-State Sensors, Actuators, and Microsystems Dig.Tech. Papers , 2005, vol. 2, pp. 2069-2073.

[8] H. Zhang, J. Kim, W. Pang, H. Yu, and E.S:Kim, 5GHz lLow -phase-noise Oscillator Basedon FBAR with Low TCF, Int. Conf. on Solid-State Sensonrs, Actuators, and Microsystems Dig.Tech. papers , 2005, vol. 1, pp. 1100-1101.

[9] E. Lee, L. Mai, and G. Yoon, Development of High-Quality FBAR Devices for WirelessApplications Employing Two Step Annealing Treatments in IEEE Microwave and WirelessComponents Letters , vol. 21, no. 11, November 2011.

[10] M. Norling, J. Berge, and S. Gevorgian Paraeter extraction for tunable TFBARs based onBaxSr 1-xTio3 in IEEE MTT-S Int. Microwave Symp. Dig. , 2009, pp. 101-104.

[11] K. M. Lakin, G. R. Kline, and K. T. McCarron, High -Q microwave acoustic resonators andfilters, IEEE Trans. Microwave. Theory Tech ., vol. 41, no. 12, pp. 2139-46, 1993.


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[12] J. D. Larson III, P. D. Bradley, S. Wartenburg, and R.C Ruby, Modified Butterworth -VanDyke circuit for FBAR resonators and automated measurement system, in Proc. IEEE Ultrason.Symp., 2000, pp. 863-868.

[13] S. Gevorgian, a Vorobiev, and T. Lewin, dc field and temperature dependent acoustic

resonances in parallel-plate capacitors based on SrTiO[sub 3] and Ba[sub 0.25]Sr[sub0.75]TiO[sub 3] films: Experiment and modeling, Journal of Applied Physics , vol. 99, 2006, p.124112.

[14] J. Berge and S. Gevorgian, Tunable bulk acoustic wave resonators based onBa0.25Sr 0.75TiO3 thin films and a HfO2/SiO2 Bragg reflector, in IEEE Transactions onUltrasonics, Ferroelectrics and Frequency Control, vol. 58 ,no. 12, 2011, pp. 2768-2771,

[15] Nave. R. (2010). Relaxation Oscillator Concept. Available: http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/relaxo.html. Last accessed 16th April 2012.

[16] A. R. Hambley, Electronics , 2nd ed., Prentice Hall, 2000, pp.636-640.

[17] S.G Burns and R.S:Ketcham, Fundamental -mode Pierce oscillators utilizing bulk-acoustic-wave resonators in the 250-300MHz range, IEEE Trans.Microw.Theory Tech. , vol.MTT-32,no.12,pp.16668-1671,Dec.1984.

[18]Y.S.Park,S.Pinkett,J.S.Kenney,and W.D:Hunt,A 2.4 GHz VCO with an integrated acousticsolidly mounted resonator, in Proc.IEEE Ultrason. Symp .,2001,pp.839-842.

[19] A.Khanna,E.Gane,and T.Chong, A 2 GHz voltage tunable FBAR oscillator, in IEEE MTT-S Int. Microwave Synp. Dig .,2003,pp. 717-720.

[20] J.J Kim, H. ZHANG, W. Pang, H. Yu, and E.S: Kim, low phase -noise FBAR-basedvoltage controlled oscillator without varactor, in Proc. IEEE solid-state Sensors, Actuators andmicrosys .,2005,pp.1063-1066.

[21] P. Vincent, J. B. david, I. Burciu, J. Prouvee, C. Billard, C. Fuchs, G. Parat, E.Defoucaud,and A. Reinhardt, A 1 V 220 MHz -tuning-range 2.2 GHz VCO using a BAW resonator, in

IEEE Int. Solid-State Circiuts Conf. Dig. Papers , 2008, pp. 478-479.

[22] S. Dossou, N. Abele, E. Cesar, P. Ancey, J.F. Carpentier, P. Vincent, and J. M. Fournier,

60 W SMR BAW oscillator designed in 65 nm CMOS technology, in IEEE Int. Symp. CirciutsSyst. Dig. Papers , 2008, pp. 1456-1459.

[23] P.Guillot, P.Phlippe, C.Berland, and J.F. Bercher, A2 GHz 65 nm CMOS digitally -tunnedBAW oscillator, in Proc. IEEE. Int. Conf. Electron. Circuits Syst. , 2008, pp. 722-725.


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[24] H. El-Aabbaoui, J.-B. David, E. D. Foucauld, and P. Vincent,Ultra low phase noise 2.1GHz Colpitts oscillators using BAW resonator. in IEEE MTT-S Int. Microwave Symp. Dig .,2009, pp. 1285-1288.

[25] A. Nelson, J. Hu, J. Kaitila, R. Ruby, B. Otis, A 22_W, 2.0GHz FBAR Oscillator. in

IEEE Radio Frequency Integrated Circuits Symp (RFIC). , 2011[26]. M. Norling, J. Enlund, S. Gevorgian, and I. Katardjiev, A 2 GHz oscillator based on asolidly mounted thin film bulk acoustic wave resonator, in IEEE MTT-S Int. Microwave Symp.

Dig. , 2006, pp. 1813-1816.

[27] Kim B. Ostman, and al., Novel VCO Architecture Using Series Above-IC FBAR and Parallel LC Resonance ,in IEEE J. of Solid-State circuits, vol. 41, no. 10, October 2006

[28] J. Shi, B. Otis, A Sub -100W 2GHz Differential Colpitts CMOS/FBAR VCO, in IEEE

Custom Integrated Circuits Conf (CICC)., 2011 [29] Rainee N. Simons, Coplanar Waveguide Circuits , Components , and Systems. John Wiley &Sons, Inc. 2001

[30] D. A. Blackwell, D. E. Dawson, and D. C. Buck, X -Band MMIC Switch with 70dB Isolation and 0. 5 dB Insertion Loss, 1995 IEEE Microwave Millimeter-Wave

Monolithic Circuits Symp. Dig ., pp. 97 100, Orlando, FL, May 15 16, 1995.

[31] A. Borgioli, Y. Liu, A. S. Nagra, and R. A. York, Low -Loss Distributed MEMSPhase Shifter, IEEE Microwave Guided Wave Lett ., Vol. 10, No. 1, pp. 7 9,

January 2000.[32] L. W. Martin, Y.H. Chu, and R. Ramesh. Advances in the growth and characterization ofmagnetic, ferroelectric, and multiferroic oxide thin films . Mater. Sci. Eng ., R, 68(4-6):89-133,May 2010

[33] R. Easen. pulsed laser deposition of thin films. Applications-led growth of functionalmaterials . Wiley, 2007.

[34] A. Namaki, T. Kawaki, and K. Ichinge. Angle-resolved time of- flight spectera of neytral particles desorbed from laser irradiated CdS . Surf. Sci ., 166(1), 1986.
http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=6045019http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=6045019http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=6045019


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Appendix1: Tunable FBAR Resonator MBVD model ExtractedParameters

Fig.1T unable FBAR resonator MBVD model ext racted parameters (a) series and parallel resonance frequencies(b) series and parallel Q facto rs (c) effective coupling coefficient (d) impedance magnitude

(a) (b)

(c)

(d)

I m p e

d a n c e m a g n i t u

d e

, ( O

h m s )


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Appendix2: Transmission line parameter extraction

Conversion S-parameter to ABCDConversion of S to ABCD-parameter is given in [1]

ABCD network for Transmission line

,Z0

Zo is a characteristic impedance of the transmission line.

is the length of the line. Note that

+ Complex propagation constant= attenuation constant NP/m

= wave propagation constant

)cosh()sinh(

)sinh()cosh(

o

o

Z

Z

2112221121122211

2112221121122211

211111

1

1111

2

1

S S S S S S S S Z

S S S S Z S S S S

S DC

B A

o

o


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For a Lossless line

= 0

When the transmission line is lossless this reduces to

For TEM wave propagation the effective permittivity and Loss tangent can be obtained from [1]

Where

Where is the attenuation constant due to dielectric in NP/m.

Extracted parameter for CPW from ADS momentum simulation are plotted from 0 to 20 GHz inFig. 1(a),(b),(c).

)sin()sinh( k j jk

)cos()sin(

)sin()cos(

k Z

k j

k jZ k

o

o

)cos()cosh( k jk


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Appendix3: Fabrication Steps and recipe

Note: the thicknesses are not to the same scale

Process Recipe Schematic1.New sample includingBragg reflector

Parameters:Hfo2 260nm/SiO2 284nm(3 pairs)

Size:10 10 mmThickness:501 m

2.Cleaning Tool: Wet bench

Parameters: Acetone,Ultrasonic bath for 3 min @100% power

Intention: To clean the photoresist used for protecting thewafer during cutting

3.TiO2 Deposition Tool: Sputter

NORDIKO 2000 Parameters: Ti and O2 for 8min.

Intention: To deposit Tio2 onthe sample for better adhesion between Sio2 and Pt.

4.Platinum Deposition Tool: Sputter NORDIKO 2000

Parameters:Pt for 2 min @60 w

Intention: To deposit Pt on thesample as the bottomelectrode

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con


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pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con


Parameters: Acetone,Ultrasonic bath for 3 min @100% power

Intention: To clean surfacefrom impurities beforeapplying the photo resist

6.Resist applying andspinning

Tool: Hot plates and resistspinner

Parameters: photo resist S1813 @4000rpm

for 30 sec.Hot Plates@ 900 C for 1 min.

Intention: To apply resistevenly on the sample for edgeremoval

7.Photo resist pattering-I(edge removal)

Tool: Mask aligner KS MJB3-UV 400

Parameters:Soft contact, exposure time 1

min.Intention: To remove resistedges

8.Developing Tool: Wet bench

Parameters:

Developer MF-319 for 1.5min.

Intention: To develop exposedresist edges

pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con


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pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

9.Photo resist patterning -II Tool: Mask aligner KS MJB3-UV 400

Parameters: soft contact,exposure time 15 sec.

Intention: To expose photoresist according to the bottomelectrode mask pattern


Parameters:

Developer MF-319 for 15sec.

Intention: to develop theexposed photo resist

11.Etching Tool: Ion Beam MillingOxford Chamber.

Parameters: Argon gas flowfor 20 min.

Intention: To pattern the Pt bottom electrode layer

12.Resist removal Tool: Wet bench, Ultra sonic bath

Parameter: Micropositremover @750C Ultra sonic bath @%100 for 10 min.

Intention: to remove photoresist

pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

o 6 nm

con


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pt 1 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

BSTO 234nm

pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

BSTO 234nm

pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

13.Oxygen plasma strip Tool: Plasma Therm BatchTop

Parameters:O2 plasma for 1min @ 250 W.

Intention: to remove organicresidue from photo resists.

14.BSTO deposition Tool: Pulsed LaserDeposition-(PLD)

Parameters: Target BSTOTemperature 620-640o C-3100 laser pulses in 5 min.

Intention: To deposit BSTOfilm


Parameters: Acetone

Intention: to clean the sample

surface after BSTO depositionReady to be taken to the maincleanroom

16.LOR Lift off- Resist Tool: Wet bench Hot plates Resist spinner

Parameters: LOR 3A@4000rpm for 1 min.

Hot plates: 5 min@ 1900

C.Intention: Coat and prebakeLOR

BSTO 234nm

pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con


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17.Coat and prebake imagingresist

Tool: Wet bench Hot plates Resist spinner

Parameters: Photo resistS1813@4000 rpm for 30 sec.

Hot plates @1100

C for 2 min.Intention: Coat and prebakeresist making it ready for patterning.

18.Expose imaging resist Tool: Mask aligner KS MJB3-UV 400

Parameters: soft contactexposure time 10 sec.

Intention: To expose photoresist according to the SiO2 mask pattern

19.Develop the resist andLOR

Tool: Wet bench

Parameters: Developer MF-319 for 2 min

Intention: To develop theresist and LOR for SiO2sputtering.

BSTO 234nm

pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

BSTO 234nm

pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

BSTO 234nm

pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con


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soluble

23.Exposure using invertedmask


Parameters: exposure time 6

secIntention: to expose thesample for Gold depositionand patterning(the gold layerfinally remains at exposedarea)

24.Reversal bake Tool: Hot platesParameters: 1250C for 2 min.

Intention: To make theexposed area inert while theunexposed area remains photoactive.

25.Flood exposure withoutmask


Parameters: flood exposurefor 60 sec.

Intention: makes the resists,which was not exposed at previous step, soluble indeveloper.

BSTO 234nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

BSTO 234nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

BSTO 234nm

p t 1 0 0 n m

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con


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Parameters: Developer AZ351 B for 1 min

Intention: To develop theresist according to the mask pattern

27.Gold Deposition Tool: AVAC E-beamevaporator.

Parameters: 8.8 / sec toreach 0.5 m gold thickness.

Intention: To deposit the Goldlayer on the sample.

28.Lift-off Tool: Wet bench

Parameters: Acetone @750 Cfor 5 min.

Intention: To remove the extraGold and have the pattern onthe sample.

BSTO 234nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

BSTO 234nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

BSTO 234nm

pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con


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29.Deposition of Aluminumtop electrode (same procedureas the Sio2 Layer)

Tool: FHR MS 150x4-L

Parameter: Al deposition for51 sec.

Intention: To deposit and pattern the Al layer on thesample.

BSTO 234nm

pt 100 nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

Sio2 284nm

Hfo2 260nm

con

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