Microsystems and Smart Sensor Interfaces: A Reviewims.unipv.it/~franco/JournalPaper/73.pdf · Microsystems and Smart Sensor Interfaces: A Review 13 Fig. 4. Cantilever array achieved

Analog Integrated Circuits and Signal Processing, 15, 9–26 (1998)c! 1998 Kluwer Academic Publishers, Boston. Manufactured in The Netherlands.

Microsystems and Smart Sensor Interfaces: A Review

FRANCOMALOBERTI AND PIERO MALCOVATIIntegrated Microsystem Laboratory, Department of Electronics, University of Pavia, Via Ferrata 1, 27100, Pavia, Italy

[email protected], [email protected]

Received February 19, 1997; Accepted May 23, 1997

Abstract. Future integrated microsystems will benefit significantly from progress in the VLSI field. Two keyelements will boost the implementation of new micro-integrated architectures: progress in batch-manufacturedsilicon sensors and the introduction of new circuit techniques for designing interface circuits. These two factorswill be essential in favoring the transition from the present “research driven speculations” to “customer drivenactivities”. This paper discusses the key issues in realizing microsensors and the most suitable circuit techniquesfor interfacing and processing their output signals. A number of examples of integrated structures will illustratepresent problems and possible solutions.

Key Words: micorsensors, interface, microsystem, smart sensor

1. Introduction

Conventional integrated circuit (IC) technologies and,when necessary, a few additional post-processing stepsallow us to realize on a silicon chip a number of sens-ing structures capable of detecting various physical andchemical quantities with reasonable sensitivity [1], [2],[3], [4]. The same materials (silicon, polysilicon, alu-minum and dielectrics) used to fabricate integrated cir-cuits are exploited to realize sensors. If the process-ing steps of conventional IC technologies are insuffi-cient, additional operations can be performed to fabri-cate a particular sensor after the completion of the con-ventional IC process flow (postprocessing steps), thusleaving the IC features unchanged. This approach al-lows batch manufacturing of both the integrated circuitand the sensing elements. Consequently, cost effectivemicrosystems including sensors, circuits and eventu-ally actuators can be fabricated, opening new perspec-tive markets. Challenges arise from the technology,the level of the sensor signals, the packaging require-ments, the testing of physical-electrical (or chemical-electrical) systems, the aggressive environment andeven the signal processing functions required.Profitable use of smart sensors in real products de-

pends on a number of issues such as cost-effective pro-duction, reliability, easy and inexpensive testing andcompensation of parasitic effects and non-idealities(for example temperature dependencies). All of theseissues will be considered in the following discussion.

2. Microsystem Design

The development of an integrated microsystem is asystem development, demanding the same attentionsneeded for conventional electronic systems. In addi-tion, the design of a microsystem requires interdisci-plinary knowledge, including sensor technology, ana-log signal conditioning, signal processing, digital inter-facing and actuator control. The first step in a systemdevelopment is the definition of the system require-ments or, rather, understanding the customer’s needs.In this phase the contributions of experts on siliconsensor design, circuit design, and signal processing areessential.Once the specifications of the system are outlined,

possible silicon sensors and signal processing architec-tures must be defined. The testing issues (testability,design for testing and testing procedures) also have tobe considered at this early stage. We have to rememberthat testing a system is quite different from testing anintegrated circuit, because we have to handle physicalor chemical quantities as well as electrical variables.Fortunately, the bandwidth of the sensor signals is nor-mally fairly low. On the other hand, the amplitude ofthese signals is often limited and they are corrupted bynoise. Moreover, the environment where the systemoperates can be harsh and hostile, leading to severeconditions of use (such as high or low temperature,high humidity and high pressure).An important issue in integrated microsystem pro-

10 F. Maloberti and P. Malcovati

duction is encapsulation. The main function of con-ventional integrated circuit packages is protecting thecircuit from the environment. Dissipation of powerconsumed and shielding from EM interferences aresecondary requirements. By contrast, in a microsen-sor system, the physical or chemical measurands haveto (selectively) reach the chip, often leading to prob-lems associated with the rejection of undesired spur oraggressive quantities.Cost is another important issue. Batch manufac-

turing allows costs to be reduced. Moreover, systemminiaturization, lower voltage and lower power con-sumption make the integrated microsystem even moreattractive. Nevertheless, the cost/benefit ratio is themajor aspect attracting the customer. It is worthwhilepointing out that low cost does not only mean lowerprice, but easy use, reliability and superior performanceas well.All of these arguments clearly show that a break-

through in microsystems and smart sensors does notonly depend on technological progress but also on aproper focusing of “practical issues” that should ex-pand the researchers’ area of interest to what we coulddefine “customer driven investigation”.

3. Silicon Sensor Technologies

In this section, we discuss some of the postprocessingsteps used to fabricate sensors [1], [2], [3], [4]. Thesesteps can be classified into two major categories:

• micromachining;• deposition of material.In micromachining, part of the material forming

the chip (silicon, polysilicon, silicon oxide, silicon ni-tride or aluminum) is removed in order to realize mo-bile structures or ensure a thermal insulation (some-times, micromachining is used to lower parasitic ca-pacitances).Deposition of special materials in the form of thin

layers helps to procure or enhance sensitivity to somespecific quantities. Examples are the deposition ofpolymers to sense gases and humidity or the deposi-tion of magnetic coatings to concentrate the magneticfield and fabricate inductors.Etching is used to manufacture micromachined

structures. As usual, we can distinguish betweenisotropic etching and anisotropic etching. In the fol-lowing paragraphs, we quickly recall the features ofthese techniques and their specific use inmicromachin-ing.

Isotropic Etching

The etching is called isotropic when it proceeds uni-formly in all directions. The isotropic feature is notvery positive for modern IC processes since it causesthe so-called under-etching effect, which is responsi-ble formismatch between capacitorswith the same areabut different perimeters.By contrast, isotropic etching is beneficial in sensor

technology since it allows us to use sacrificial layers toremove material under free microstructures. To betterunderstand this point, Fig. 1 shows the steps requiredto realize a capacitive microbridge. On the top of adiffused pattern, a passivation layer made of siliconnitride and a sacrificial layer made of a p-doped sil-icon dioxide are deposed. A successive polysiliconpattern defines the microbridge structure. Finally, thelateral isotropic etching removes the sacrificial layerreleasing the polysilicon micro-bridge which becomesmoveable. Isotropic etching is typically based on aliquid acid or a liquid base (for example HF is widelyused for etching silicon dioxide).The isotropic etching allows us to remove sacrifi-

cial layers under structures as wide as 20 to 30 mm.However, the etching rate is normally low (at low tem-peratures), requiring several hours to release structuresof a few tens of mm. Of course, the etchant used mustbe selective, since it should not attack other parts of thestructure or the protective photoresist.

Anisotropic Etching

Anisotropic etching removesmaterial at an etching-ratethat is not even in all directions. Some etching solutionsshow a crystallographic anisotropy, where the etch ratedepends on the crystal plane that is etched. For exam-ple, the EDP etchant (Ethylenediamine pyrocatecholin water solution) shows an etching rate in the (110)and (100) directions which are at least 50 times largerthan the etching rate in the (111) direction. Higher in-dex planes are typically highly attacked by the etchant.The exploitation of these features leads to the fabrica-tion of predictable 3D silicon structures. For example,Fig. 2a, represents the result of the anisotropic etchingof a square window in (100) silicon. The etching rate inthe (111) directions is negligible; therefore, the chemi-cal erosion of thematerialmainly proceeds perpendicu-larly to the (111) crystallographic planes (54.7" slope).When the depth reachesd = L/[2 tan(54.7")] the inter-

Microsystems and Smart Sensor Interfaces: A Review 11

Fig. 1. Postprocessing steps for a polysilicon micro-bridge realization.

Fig. 2. Anisotropic etching of silicon.


Fig. 3. Membrane achieved by bulk micromachining.

section of the two (111) planes brings the etching-rateto a negligible value and the etching procedure stopsautomatically.If the mask has convex corners, the etching in the

(100) and (110) directions exposes the planes with highindex to the erosion of the etchant, thus leading to un-deretching under the corner itself. This effect is shownin Fig. 2b.A key issue in the design of defined structures is the

etch-stop (interrupting the etching procedure at a givendepth). Etch-stop is obtained with various techniques:

• by controlling the etch time: a fresh etchant witha low etching rate produces an etching depth con-trollable with acceptable accuracy;

• by exploiting the etch-stop at a given interface:some etchants are active with specific layers,while for other layers the etching-rate drops tonegligible values (for example KOH and EDP donot attack highly doped p-type silicon);

• by electrochemical etch-stop: when the etchingreaches an electrochemical barrier (like the limitof a p-n junction), anodic oxide grows on the sur-face, thus stopping the etching process, and anelectrical “signal” indicates that such a barrier hasbeen reached.

The techniques described above allow us to performboth bulk micromachining and surface micromachin-ing. In bulk micromachining, silicon is post-processedfrom the back of the wafer, allowing thin membranesto be achieved (Fig. 3). In this case the bulk silicon isremoved up to the etch-stop interface, usually silicondioxide or a p+ layer.With surface micromachining the etching carves the

silicon from the top. The undercut through high in-dex planes allows us to obtain cantilever or suspendedbridges. Fig. 4 shows the SEM microphotograph of acantilever beam.

Deposition of Materials

The deposition of thin layers of material is a commonoperation in both standard IC technologies and mi-crosensor fabrication. However, in microsensor fab-rication the temperature of the process must be lowin order to preserve the IC features unchanged. Thetechniques used are: spinning, electroplating, sputter-ing, and other specific low temperature technologies.Possible deposed materials are:

• polymer based films, which are sensitive to hu-midity or gas;

• permalloy layers, capable of increasing the mag-netic sensitivity;

• piezoelectric materials (like zinc oxide) that sensepressure and stress;

• biocomponents (enzymes) for sensing biologicalquantities.

The major technological concerns in deposing thinlayers are adherence of the layer to the substrate, mis-matches in the temperature expansion coefficients, ag-ing, and reliability of the layers.

4. Sensor Interfaces

A microsensor, similarly to all conventional sensors,generates an electric signal in the form of voltage, cur-rent, resistance or capacitance variation. The desiredsignals can have a very small amplitude, dangerouslyclose to the noise floor, or they can be mixed with un-desirable signals located in different frequency bands.The function of the interface circuits is to extract theneeded features of the signal and, often, convert the sig-nal into the digital domain. Different situationsmust befaced. In the following paragraphs, we will discuss thetypical signal processing requirements coming from anumber of microintegrated systems belonging to oneof these categories:

• system based on sensorsmadewith IC technologyunchanged;

• system with sensors based on bulk micromachin-ing;

• system with sensors based on surface microma-chining;

• system based on sensors based on deposition ofmaterials.


Fig. 4. Cantilever array achieved with surface micromachining.

Optical Sensor Systems

Conventional CMOS technologies allow us to designoptical photodiodes with acceptable sensitivity in thevisible and near infrared spectrum. A photodiode con-sists of a p-n junction realized with the substrate andthe drain/source diffusion of anMOS transistor. Wave-lengths ranging from 0.4 to 1 µm generate electron-hole pairs in the silicon bulk. The electric field of thereversely biased p-n junction, then, separates electronsfrom holes, thus allowing the generated photo-chargeto be collected. Fig. 5a shows an array of photodi-odes arranged in a x-y matrix [5]. In this case thephoto-charge is temporarily stored in the parasitic ca-

pacitance of the diode itself. When a diode is selected,the stored charge is measured and, at the same time, thereverse biasing of the photo-diode is set. The circuitrequires both digital and analog signal processing func-tions. The digital section controls the diode selection,while the analog part transforms the photo-charge intoa voltage by means of one or more charge preampli-fiers.A typical structure of a charge preamplifier is shown

in Fig. 5b. The read-phase is divided into two parts.First, the charge on the photo-diode is integrated oncapacitor CF while the voltage across the photo-diodeapproaches VREF . Then, capacitor CF is discharged(to be ready for a new conversion cycle), setting the


Fig. 5. Photodiode microsystem: (a) photodiode array and (b) interface circuits.

photodiode voltage at VREF . The error caused by theoffset of the gain stage A is therefore cancelled.

Magnetic Sensors

Another physical quantity that we can detect with anunchanged conventional IC technology is the magneticfield. Two possible devices based on the Lorentz effectare shown in Fig. 6.The current controlled Hall device (Fig. 6a) is sensi-

tive to a magnetic field orthogonal to the chip plane [6].The current I1 injected into one of the terminals is splitinto three parts. The major part, I2, flows through the

central terminal, while a small fraction flows throughthe two lateral terminals. In the presence of a magneticfield, the Lorentz force produces an imbalance betweenthe two lateral components, which is measured by theon-board electronics.The LMT (lateral bipolar magnetotransistor) device

(Fig. 6b) [7] is similar to the lateral bipolar transis-tor available in CMOS technology, but with two sepa-rate collectors. The magnetic field parallel to the chipsurface produces an imbalance in the lateral collectorcurrents which is measured by the on-board interfacecircuits. Both the devices considered are capable ofdetecting magnetic fields in the mT range.The LMT structure can be made bidimensional [8]


Fig. 6. Magnetic sensors in CMOS technology: (a) top view of a current controlled Hall device and (b) cross-section of a lateral bipolarmagnetotransistor.

Fig. 7. Microphotograph of a 2D magnetic sensor.

by adding two additional collectors. The resulting2D magnetic sensor, in combination with a permanentmagnet, is suitable for accurate contactless angle mea-surements inwear-free angular positioning control sys-tems. Fig. 7 shows the microphotograph of a 2D-LMT.It has one central emitter and four lateral collectors.A suitable processing of the four collector currents

allows themagnetic field direction to bemeasured. Theblock diagram of the sensor interface used for this ap-plication is shown inFig. 8. It consists of a 2Dmagneticmicrosensor, a circuit for biasing and common moderejection, a current to voltage converter, two 10 bit D/Aconverters performing offset compensation and a sig-

nal processing circuit capable of calculating the ratioof the two field components parallel to the chip plane.The output of the system is a digital word which rep-resents the angular position of the permanent magnet.The angle is measured over the full 360" range with aresolution of 6 degrees (actually resolutions as low as1 degree can be achieved).The interface circuit is based on an incremental A/D

converter (Fig. 9) which exploits the oversamplingtechnique to translate the analog signal into the dig-ital domain. The oversampling approach is very con-venient when processing band limited signals, sincespeed is tradedwith accuracy andhigh resolution canbe


Fig. 8. Block diagram of the magnetic sensor interface.

Fig. 9. Schematic of the incremental A/D converter.


Fig. 10. Operating principle of the incremental A/D converter.

Fig. 11. Microphotograph of the magnetic microsystem chip.


Fig. 12. Differential non-linearity of the digital output as a functionof the magnetic field angle.

achievedwithout requiring precise components. More-over, the oversampling allows us to avoid complex anti-aliasing filters.In this case, the differential voltages VX1 # VX2 and

VY1#VY2, provided by the current to voltage converter,are used alternatively as the input or the reference signalfor the incremental A/D converter, depending on thequadrant of the magnetic field angle Q (actually, theinput clock phases vary according to Q). The correctvalue of Q is determined by a finite state machine inthe digital section, as shown in Fig. 10.Once the quadrant is determined, the bitstream de-

livered by the A/D converter is decimated by a counter,producing an output word N proportional to the ra-tio between the magnetic field components. Finally, a

Fig. 13. Microsystem for IR sensing.

look-up table transform N in the magnetic field angleusing a gray code representation. The chip micropho-tograph of the chip including the complete system isshown in Fig. 11. It can be observed that the analogand the digital sections have been carefully separated,in order to minimize the crosstalk. The total chip area(including pads) is 6.8 mm2.The differential non-linearity of the digital Gray

code output of the system as a function of the mag-netic field angle is shown in Fig. 12. It can be observedthat the achieved step-size is 6.625" ±0.1" (0.1" is alsothe accuracy of the measurement).

IR Sensor

We have seen that bulk micromachining allows us torealize thermally insulatedmembranes. A selected partof a chip can hence be heated by an external infraredradiation (IR) flow. Thermal insulation means that thetemperature of the membrane rises in comparison withthe silicon bulk (Fig. 13). Thus, the temperature dif-ference achieved gives a measure of the IR flow.A convenient device for on-chip temperature detec-

tion is the thermopile. The thermopile is the series con-nection of a large number of thermocouples consistingof poly1 (n-doped) and poly2 (p-doped) lines. The sig-nal resulting from a small IR flow (for example emittedby the human body) is in the µV range. Therefore, thetask of the electronic interface is difficult, since the cir-cuitry has to provide very low noise and low offset


Fig. 14. Autozeroed preamplifier for the IR sensor.

amplification. This difficult target can be achieved inCMOS technology by assuming the signal bandwidthto be fairly low [9]. The use of the autozero techniqueand the successive low frequency filtering of out-bandnoise components allows us to achieve the target sensi-tivity. Fig. 14 shows the input stage of the sensor inter-face. It is a four-input transconductance stage, wheretwo inputs of the transconductor are used for the signaland two for the autozerooperation. During the autozerophase, the transconductor is buffer-connected. There-fore, the offset and low frequency noise are measuredand stored in the autozero capacitors (Caz). Duringthe measurement phase the stored voltage is subtractedfrom the signal, giving rise to a clean output current.This current is integrated over a large number of clockperiods on the capacitor of the following stage to per-form the required low-pass filtering.Amicrophotograph of the infraredmicrosystem chip

is shown in Fig. 15. To ensure the maximum testingflexibility, the sensors are not directly connected to theread-out circuitry, but some pad openings are availablefor local bonding.Fig. 16 shows the output signal (waveform 1) ob-

tained by focusing chopped infrared radiation on thesensor (waveform 2 is the 3 Hz chopping signal). Thepower density of the radiation is 2 µW/mm2 (corre-sponding to a temperature difference of 3 K), and theactive area of the sensor is 0.84 mm2. The total powercollected is therefore 1.68 µW. In this case the gain ofthe amplifier is 75 dB. We can observe that the noiselevel is well below the signal level.

Pressure Sensor Interface

A micro-integrated Pirani vacuum sensor will showthe potential features of surface micromachining. Thebasic operation of a conventional Pirani gauge involvesa resistively heated wire. Molecular collisions with theheat source transfer thermal energy to a heat sink, thuscooling thewire. The collision rate varieswith pressureso the pressure is monitored by the power needed tomaintain a constant temperature difference between thewire and the heat sink.A miniaturized CMOS Pirani gauge has recently

been fabricated [10]. Fig. 17 shows a sketch of the pro-cess used. The air gap which separates the heat sourceand the heat sink is obtained by a sacrificial metal etch-ing. Postprocessing produces a suspended dielectricmembrane made of intermetal dielectric and passiva-tion layer. A meandering metal layer sandwiched be-tween these dielectrics is the heating element. The sus-pended membrane is separated from the substrate bya narrow gap, with a nominal width of 0.6 µm, whichcommunicates with the surrounding gas through thecleared etch windows. A microphotograph of the sen-sor is shown in Fig. 18.The biasing circuit used enables operation of the sen-

sor at a constant temperature difference !T betweensinker and environment [11]. The pressure is then ex-pressed by the power required to maintain !T . Twoon-chip incremental analog-to-digital converters trans-form the voltage and the current into the digital domain(with reference voltages VBG and R2 I2, respectively),providing two bitstreams at the output of the microsys-tem. Two controlled current sources M1 and M2 forcethe sensor RS to track the resistance of a reference el-ement RR (Fig. 19). This reference resistor consists ofa structure similar to the sensor but without an air gap.Hence, its thermal resistance to the silicon substrateis low and its electrical resistance does not depend onpressure.Fig. 20 shows the microphotograph of the system,

while Fig. 21 shows the measured pressure dependentvoltage signal VS and the dissipated power P . Thenominal value of RS is 170 ".

Humidity Sensor

The deposition ofmaterials after a conventional CMOSprocess allows us to sense some physical or chemicalquantities. For humidity the variation of the dielec-


Fig. 15. Microphotograph of the IR microsystem chip.

tric constant in polyimide layers is normally exploited.Fig. 22 shows a possible structure of a humidity sen-sor compatible with a conventional CMOS technology[12]. It is made of two interdigitated aluminum elec-trodes covered by a polyimide layer (ormost frequentlya layer of material sensitive to a particular chemical[13]). They realize a capacitor whose value, usingmin-imum size elements and area below 0.01 mm2, is in therange of a fraction of pF.Avariation of a fewpercentagepoints of the relative humidity causes the capacitanceto change by a few tens of aF. Such a variation can bemeasured by using the switched-capacitor technique orby embedding the sensor in a switched-capacitor sigmadelta modulator [14], [15].The schematic of the switched-capacitor, fully-

differential second order #!modulator for capacitivesensor read-out is shown in Fig. 23. Capacitor CS is

the humidity sensor while CR is a reference element,based on the same structure used for CS but not cov-ered with polyimide. Since CR is equal to the nominalvalue of CS , the circuit only measures the capacitancevariation. Voltages VS and VR set the sensitivity of thesystem to humidity and compensate the residual offsetof the humidity sensor. The reference voltage VRef setsthe full-scale signal for the humidity measurement.A microphotograph of the humidity sensing mi-

crosystem chip is shown in Fig. 24, while the digitaloutput of the system as a function of relative humidityis plotted in Fig. 25.

5. Conclusions

This paper discussed some key research issues in themass production ofmicrosystems and smart sensor sys-


Fig. 16. Measured response of the IR microsystem to a 3 Hz, 1.68 µW chopped infrared waveform.

Fig. 17. Pressure sensor before (a) and after micromachining (b) silicon (1), oxide (2), passivation (3), pad (4), sacrificial metal (5), accesswindow for gas (6), heater (7).


Fig. 18. Microphotograph of the Pirani sensor.

Fig. 19. Block diagram of the pressure sensor microsystem.

tems. The design and the integration of sensors andelectronics on the same silicon substrate is very impor-tant for batch manufacturing with its consequent re-duction of costs. A number of examples of integratedstructures are used to illustrate present problems andpossible solutions. Although the microsystems pre-sented in this paper are useful for related industrialapplications, more engineering work is still required tobring these devices to market maturity. Packaging, inthe first place, is currently in progress. Themain task ofintegrated circuit packages is to protect and insulate thechip from the environment. Microsensors, however,needing exposure to the measurand, require dedicatedpackaging techniques. Another important issue to beaddressed is post-production testing. Silicon foundriesuse very expensive equipment and procedures for auto-matically testing integrated circuits. These instrumentsapply directly the required electrical signals to the chipand measure the resulting output. For microsystems,however, tests involving physical and chemical quan-

tities must be performed on the chip, thus requiringfurther equipment and dedicated procedures. We hopethat a combined effort from industries and universitieswill soon cover these issues and demonstrate the effec-tiveness of microsensor and microsystem research interms of million of parts per year and billions of dollarsales.

6. Acknowledgments

The present work is the result of a long and close coop-eration with the Physical Electrical Laboratory, ETH,Zurich, headed by Prof. H. Baltes.

References

1. H. Baltes, “CMOS as sensor technology.” Sensors and Actua-tors A. 37–38, pp. 51–56, 1993.

2. S. Middelhock and S. A. Audet, Silicon Sensors. AcademicPress: London, 1989.

3. H. Baltes, D. Moser, E. Lenggenhager, O. Brand, andD. Jaeggi, “Thermomechanical microtransducers by CMOSand micromachining,” Micromechanical Sensors, Actuatorsand Systems, DSC-32, ASME, New York, NY, pp. 61–75,1991.

4. H. Baltes, O. Paul, J. G. Korvink, M. Schmeider, J. Buhler,N. Schneeberger, D. Jaeggi, P. Malcovati, M. Hornung,A. Haberli, M. von Arx, F. Mayer, and J. Funk, “IC MEMSmicrotransducers.” IEDM ’96 Technical Digest, pp. 521–524,1996.

5. A. Sartori, F. Maloberti, A. Simoni, and G. Torelli, “A 2Dphotosensor array with integrated charge amplifier.” Sensorsand Actuators A, 46–47, pp. 247–250, 1995.

6. P. Malcovati, R. Castagnetti, F. Maloberti and H. Baltes, “Amagnetic sensor with current controlled sensitivity and reso-lution.” Sensors and Actuators A, 46–47, pp. 284–288, 1995.

7. R. Castagnetti and H. Baltes, “Bipolar magnetotransistors andtheir trade-off’s.”Sensors andMaterials, 5, pp. 339–346, 1994.

8. A. Haberli, M. Schneider, P. Malcovati, R. Castagnetti, F. Mal-oberti, and H. Baltes, “2DMagnetic microsensor with on-chipsignal processing for contactless angle measurement.” IEEE J.Solid-State Circuits, 31, pp. 1902–1907, 1996.

9. P. Malcovati, C. Azeredo Leme, R. Lenggenhager, F. Mal-oberti, and H. Baltes, “Low noise multirate SC read-out cir-cuitry for thermoelectric integrated infrared sensors.” IEEETrans. Instrumentation and Measurement, 44, pp. 795–798,1995.

10. O. Paul andH.Baltes, “Novel fullyCMOS-compatible vacuumsensor.” Sensors and Actuators A, 46–47, pp. 143–146, 1994.

11. A. Haberli, O. Paul, P. Malcovati, M. Faccio, F. Maloberti, andH. Baltes, “CMOS integration of a thermal pressure sensorsystem,” in Proceedings of ISCAS ’96, 1, 1996, pp. 377–380.

12. T. Boltshauser and H. Baltes, “Capacitive humidity sensors inSACMOS technology with moisture absorbing photosensitivepolyimide.” Sensors and Actuators A, 25–27, pp. 509–512,1990.


Fig. 20. Microphotograph of the integrated microsystem: pressure and reference sensors (1), front-end interface (2), bandgap (3) incrementalanalog-to-digital converters (4, 5).

Fig. 21. Measured response of the pressure sensor.


Fig. 22. Humidity sensing capacitor.

Fig. 23. Schematic of the second order SD modulator.


Fig. 24. Microphotograph of the humidity sensor microsystem chip.

Fig. 25. Digital output of the humidity sensor microsystem.

13. C.Cornila, R. Lenggenhager, P.Malcovati, H.Baltes, A.Hiele-mann, G. Noetzel, U. Weimar, and W Goepel, “Capacitivesensors in CMOS technology with polymer coating.” Sensorsand Actuators B, 24–25, pp. 357–361, 1995.

14. P. Malcovati, A. Haberli, F. Mayer, O. Paul, F. Maloberti, andH. Baltes, “Combined air humidity and flow CMOSmicrosen-sor with on-chip 15 bit sigma-delta A/D interface,” in VLSICircuit Symposium ’95 Digest of Technical Papers, pp. 45–46,1995.

15. P. Malcovati, CMOS Thermoelectric Sensor Interfaces, Ph.D.Thesis, No. 11424, ETH Zurich, Zurich, Switzerland, 1996.

Franco Maloberti received the Laurea Degree inPhysics (Summa cum Laude) from the University of


Parma in 1968. He joined the University of L’Aquila,then the University of Pavia. For the years 1975–79, hewas technical coordinator of the Engineering School atthe University of Mogadishu, Somalia. He was visit-ing Professor at ETH-PELZurich in spring 1993. He iscurrently Professor of Microelectronics at the Univer-sity of Pavia, and is also head of the Micro IntegratedSystems Group. His professional expertise is in the de-sign, analysis and characterisation of integrated circuitsand analogue digital applications, mainly in the areasof switched capacitor circuits, data converters, inter-faces for telecommunication and sensor systems, CADfor analogue and mixed A-D design. Dr. Maloberti haswritten more than 180 published papers, 2 books andholds 14 patents (2 pending). He was the recipient oftheXII Pedriali Prize (1992) for his technical and scien-tific contributions to national industrial production. Hewas co-recipient of the IEE Fleming Premium (1996)for the paper “CMOS Triode Transistor Transconduc-tor for high-frequency continuous-time filters.” He re-ceived the Dr. Honoris Causa in Electronics awardedby Inaoe (Instituto Nacional de Astrofisica, Optica yElectronica), Puebla, Mexico in November 1996. Hehas been responsible, at both technical and manage-ment levels, for many research programmes including10 ESPRIT projects. He organised the first Special Ac-tion for Microelectronics in Italy (I-SMILE, ESPRITframe); he was the CEC representative in the advisoryboard of Special Actions I-SMILE,MEPI and SUMIS;he was in the Steering Board of the European ActionsEUROCHIP and Combined Action; he was member ofthe ExecutiveBoard of the ESPRITProjectMEDCHIP.Dr.Maloberti also served the European Commission as

ESPRIT projects’ evaluator and reviewer. He servedtheAcademyof Finland (1996) for the evaluation of theelectronic research in Finland. Dr.Maloberti is a mem-ber of the AEI (Italian Electrothecnical and ElectronicSociety), a Fellow of the IEEE (1996), Vice-PresidentRegion 8 IEEE-CAS (1995–97), a member of the Ed-itorial Board of Analog Integrated Circuits and SignalProcessing, a member of ESSDERC/ESSCIRC Steer-ing Committee, and he was a member of the SteeringCommittee of the CEC Network NEAR (Network ofEuropean Analogue Research).

Piero Malcovati was born in Milano, Italy in 1968.He received the “Laurea” degree (summa cum laude)in Electrical Engineering from University of Pavia,Italy in 1991. In the same year he received a one-year grant from SGS-Thomson, Italy. In 1992 hejoined the the Physical Electronics Laboratory at ETHZurich, Switzerland, as a Ph.D. candidate. He receivedthe Ph.D. degree in Elecreical Engineering from ETHZurich in 1996. Since 1996 he is Assitant Professor inthe IntegratedMicrosystemLaboratory atUniversity ofPavia. His research activities are focused on microsen-sor interfaces and high performance data converters.

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Microsystems and Smart Sensor Interfaces: A Reviewims.unipv.it/~franco/JournalPaper/73.pdf · Microsystems and Smart Sensor Interfaces: A Review 13 Fig. 4. Cantilever array achieved