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This is the Pre-Published Version JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 16, NO. 1, FEBRUARY 2007 29

An Integrated Floating-Electrode ElectricMicrogenerator

Wei Ma, Ruiqing Zhu, Libor Rufer, Yitshak Zohar, Fellow, ASME, and Man Wong, Senior Member, IEEE

Abstract—Microfabricated electric generators, scavengingambient mechanical energy, are potential power sources for au-tonomous systems. Described presently are the design, modeling,and implementation of a single-wafer floating-electrode electricmicrogenerator, integrating a micromechanical resonator anda number of electronic devices. Forming a plate of a variablecapacitor, the resonator is responsible for converting mechanicalvibration to electricity. A sense transistor and a diode bridgeare integrated, respectively, for monitoring the “charging” of thefloating electrode and for rectification. A lumped electromechan-ical model of the generator is developed and expressed in termsof a set of nonlinear coupled state equations that are numericallysolved. For small-amplitude excitation, a circuit based on a setof linearized equations is developed. The generator is realizedusing a compatible combination of standard complementarymetal–oxide–semiconductor (CMOS) “floating gate” process anda post-CMOS photoresist molded electroplating process. Adequateagreement between model predictions and measurement resultswas obtained. [1691]

Index Terms—Electroplating, electrostatic microelectromechan-ical systems (MEMS) device, energy scavenging, post-complemen-tary metal–oxide–semiconductor (CMOS), power generator.

I. INTRODUCTION

MICROFABRICATED systems converting vibration toelectricity could be employed to scavenge ambient

mechanical energy that otherwise would be wasted. Suchelectric microgenerators are particularly useful for poweringminiaturized systems operating in poorly accessible or hostileenvironments. The three physical principles more popularlyemployed for realizing electric microgenerators are electromag-netic [1], electrostatic [2], and piezoelectric [3]. Electrostaticis a good solution for the construction of microgeneratorsbecause of its relative ease of integration with microelectronics.The technology of microfabrication enables the creation of

Manuscript received September 20, 2005; revised March 28, 2006. This workwas supported by a the Institute of Integrated Micro-Systems, Hong Kong Uni-versity of Science and Technology, Clear Water Bay, Kowloon, Hong Kongunder a Grant. Subject Editor H. Zappe.

W. Ma is with the Department of Mechanical Engineering, Hong Kong Uni-versity of Science and Technology, Clear Water Bay, Kowloon, Hong Kong,China.

R. Zhu and M. Wong are with the Department of Electrical and ElectronicEngineering, Hong Kong University of Science and Technology, Clear WaterBay, Kowloon, Hong Kong, China (e-mail: [email protected]).

L. Rufer is with TIMA Laboratory, 38031 Grenoble Cedex, France.Y. Zohar is with the Department of Aerospace and Mechanical Engineering,

University of Arizona, Tucson, AZ 85721 USA.Color versions of one or more of the figures in this paper are available online

at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/JMEMS.2006.885856

electrostatic generators employing miniaturized, capacitiveelectromechanical transducers.

An electrostatic electromechanical transducer consists of avariable capacitor with electrodes capable of executing a relativemotion. One of the electrodes is typically implemented using apermanently charged electret. Some examples of recently im-plemented microgenerators are listed in Table I. All of these im-plementations call for the assembly of two separate substrates,one containing a mechanical resonator and another containingthe electret. Such assembly requires a nontrivial alignment ofthe substrates that hinders scaling and optimal operation of thegenerators.

In this implementation, the modeling, fabrication, and char-acterization of a single-wafer integrated floating-electrodeelectrostatic electric microgenerator are described. The electretis replaced by an insulated floating-electrode made of heavilydoped polycrystalline silicon (poly-Si) and fabricated usinga standard CMOS “floating gate” process [7]. Charged byelectron tunneling, the floating electrode works like one in aconventional nonvolatile memory device. A mechanical res-onator, which forms a counter plate to the floating electrode, isrealized using a photoresist molded low-temperature electro-plating process [8] that is compatible with the construction ofthe floating electrode. A sense transistor and a diode bridge areintegrated, respectively, for monitoring the “charging” of thefloating electrode and for rectification.

A lumped-element electromechanical model of the micro-generator is developed and described in terms of a set of non-linear, coupled state equations that are numerically solved usingSIMULINK [9]. For small-amplitude excitation, a circuit basedon a set of linearized equations is developed. The fabricatedgenerators were tested using a shaker as a source of vibration.Reasonable agreement between model predictions and measure-ment results was obtained.

II. DESIGN AND MODELING

Shown in Fig. 1 is the schematic design of the microgenerator.An electrically floating electrode made of heavily doped poly-Siis insulated on all sides by a low-stress silicon nitride. This elec-trode, together with a movable metallic electrode as the counterplate, forms a variable capacitor . It is charged by electrontunneling through a thin oxide thermally grown inside a windowopened on an insulating silicon nitride. The metallic electrodefunctions as a laterally oscillating mechanical resonator with aloop-spring design [8]. Since significant relative displacementbetween the electrodes of is possible, several cycles of vari-ation of between its maximum (fully overlapped)

1057-7157/$25.00 © 2007 IEEE

30 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 16, NO. 1, FEBRUARY 2007

TABLE IRECENTLY IMPLEMENTED ELECTRET POWER MICROGENERATORS

Fig. 1. Schematic diagrams of (a) a 2� 2 array generator and (b) a magnifiedview of the resonator over the fixed floating electrode of the generator.

and minimum (fringe) values are possible within onevibration period.

Larger output power can be obtained by linking an array ofidentical resonators with rigid coupling beams [10]. This alle-viates potential rigidity problems associated with a single largeresonator. Furthermore, array size (hence power) can be readilyscaled, while largely preserving the designed natural vibrationfrequency of the component resonators.

Shown in Fig. 2 is a lumped-element schematic representa-tion of the microgenerator. It is assumed that the floating elec-trode is fixed to the vibration frame. The variable capacitance

is approximated by that of a one-dimensional capacitor, i.e.,, where is the displacement of the

resonator with respect to an arbitrary but fixed origin and isthe displacement of the vibration frame (hence also the floatingelectrode) with respect to the same origin. is the dielectricconstant of air; is the gap spacing between the electrodes;is the total effective width of the capacitor electrodes normalto the direction of motion; and is the length of the electrodes

Fig. 2. Lumped-element electromechanical model of the microgenerator.

along the direction of motion. The resonator is modeled as aspring-mass system with a dashpot damper [11]. Mechanical vi-bration leads to changes in the relative displacement . Con-sequently, changes between when

and when . Vibrationleads to the generation of an alternating current flowing throughan external load resistor and a parasitic capacitor .

Mechanical and electrical energy conversion is coupledthrough the electrostatic field across the plates of . The force

acting on the field and the voltage generated acrosscan be derived from appropriate partial differential coeffi-

cients of the total electrostatic energystored in the coupling field [12]

(1)

(2)

where it is assumed that there are no other energy loss mech-anisms. is the instantaneous charge on . The function

if and 1 if .

MA et al.: INTEGRATED FLOATING-ELECTRODE ELECTRIC MICROGENERATOR 31

Fig. 3. Dynamic model of the microgenerator built in SIMULINK.

The mechanical resonator is governed by Newton’s secondlaw

(3)

where is the lumped mass of the resonator, is the dampingcoefficient, is the equivalent lumped spring constant, and

is the force acting on by the coupling field.The electrical part of the system is governed by Kirchoff’s

voltage law

(4)

where is the fixed floating-electrode to ground (the sub-strate) capacitance, is a parasitic capacitance, and is thenet charge stored on the floating electrode. Setting ,one recovers the differential equation [13] governing the casewithout the parasitic capacitive loading.

It can be seen in (1) that the term in (3) displaysa quadratic dependence on and the term

in (4) is nonlinear in . Con-sequently, (3) and (4) are coupled and nonlinear.

A. Large-Amplitude Solution

Due to the difficulty in obtaining closed-form solutions to (3)and (4), a numerical approach based on a set of state differentialequations is presently adopted [14]. In this approach, a givenstate of the system is described by a set of state variables, thetime derivatives of which are determined by the present valuesof the state and input variables.


Fig. 4. Linear circuit network of the microgenerator.

Denoting , , and by the respective state variables, , and , (3) and (4) can be converted to the following

set of three state equations:

(5)

and

(6)

(7)

where , when recast in termsof the state variable and the input variable . These stateequations are represented in the block diagram shown in Fig. 3and solved numerically using SIMULINK. The charge (statevariable ) is obtained as the output of the integration unitshown in the upper part of the block diagram; the displacement

and the velocity (respective state variables and )are evaluated in the lower part of the same diagram.

B. Small-Amplitude Excitation and Linearization

For small-amplitude input oscillation about a static oper-ating point, it is possible to obtain small-signal voltageand force by retaining only the first-order terms in theTaylor series expansions of (1) and (2)

(8)

(9)

where and denote the static displacements of the res-onator and the frame; ,

, and are the respective valuesof the capacitance of, the charge on, and the voltage acrossat the operating point. Notice that (8) and (9) do not apply when

, in which case must be substituted by itsabsolute value.

For , (3) and (4) can be linearized to yield

(10)

where the transformer factor. It can be seen that the coupling field behaves like a spring

with a positive spring constant .Based on (10), a linear equivalent circuit (Fig. 4) can

be constructed. The electrical and the mechanical sub-circuits are linked by an ideal transformer with a trans-former factor . The resulting linear circuit can be Fouriertransformed to yield the spectrum of the power

dissipated in as shown in (11) at the bottom ofthe page, where isthe characteristic electrical angular frequency,

is the natural mechanical angular fre-quency, is the total equivalent spring constant,

is the

(11)


Fig. 5. Dependence of the effective spring constant k and the transformerfactor � on jx � y j.

Fig. 6. Simulated dependence of the power output and the resonator displace-ment on y .

mechanical impedance induced by the electrical subcircuit, andis the damping ratio of the system.

III. SIMULATION

The values of the elements used in the models are evaluatedusing the appropriate material properties and the device dimen-sions shown in Fig. 1. The estimated values of and ofthe mechanical resonator are 2 10 kg and 138 kg/s [8], re-spectively. Consequently, the purely mechanical natural vibra-tion frequency (1 2 ) according to the linear model is

4 kHz. Based on the area of the movable capacitor plate, avalue of 1 pF for and a value of 1.9 pF for areestimated. For a net stored charge of 8 C/m , the vari-ation of and as a function of is plotted in Fig. 5.Note that is two to three orders of magnitude smaller than themechanical for m; hence it has negligible influenceon the mechanical natural vibration frequency in this range.

With a sinusoidal driving frequency of 4.2 kHz and am-plitude ranging from 1 to 2.5 m, dissipated on

M is obtained analytically using the set of linear model

Fig. 7. (a) Frequency spectrum and (b) waveform of the current response of a5 � 4 array. y = 1 �m.

(10) and numerically using SIMULINK for the set of nonlinearmodel (3) and (4). For m, the good overlap be-tween the linear and nonlinear response shown in Fig. 6 is an in-dication that the device behaves essentially linearly in this range.

For m, the spectral density [Fig. 7(a)] of the wave-form [Fig. 7(b)] of the current flowing across containssubstantially only one component at the driving frequency, asexpected for a linear system. Consequently, (11) is applied tostudy the dependence Fig. 8 of on and at m.Clearly, is maximum at kHz, close to the natural vi-bration frequency of 4 KHz. is the largest at and3.2 M , respectively, for and 16.8 pF. The latter con-sists of a contribution of 14.8 pF from the way the device islaid out and a further contribution of 2 pF from the measure-ment setup.

Nonlinearity appears gradually when is increased beyond1 m. At m, an obvious distortion in the currentwaveform Fig. 9(a) is observed, caused by the appearance of


Fig. 8. Dependence of the power output of a 5 � 4 array on driving frequency, resistance load, and parasitic capacitance calculating using the linear model.y = 0:1 �m.

Fig. 9. (a) Waveform and (b) frequency spectrum of the current response of a5 � 4 array. y = 7 �m.

the second- and higher order harmonics in the correspondingfrequency spectrum Fig. 9(b).

Fig. 10. Schematic cross-sections of the microgenerator after (a) the forma-tion of the insulated floating electrode and (b) release of the resonator. (c) Asecondary-electron micrograph of a fabricated 5 � 4 array generator.

IV. FABRICATION

The technology Fig. 10 developed to fabricate the microgen-erator consists of a conventional CMOS “front end” processto realize the floating electrode, the sense transistors, and theother electronic devices, as well as a compatible low-tempera-ture “back end” process to realize the resonator.


Fig. 11. Current–voltage characteristics of a tunnel oxide before and after break-down.

The front-end process started with conventional n-type siliconsubstrates Fig. 10(a). The active areas were defined using a“LOCOS” isolation process, using low-pressure chemical vapordeposited (LPCVD) stoichiometric silicon nitride as the oxida-tion mask. A layer of sacrificial poly-Si was added to induce asubsequent large-area etching of the underlying silicon substrateto form a buried air cavity. LPCVD low-temperature oxide (LTO)was used as a diffusion mask, and heavily phosphorus-dopedregions were created to form the tunneling and substrate contacts.A thin thermal oxide, 20 nm, was formed as the “charging” tunneloxide and the transistor gate oxide. A heavily doped poly-Si issandwiched between two layers of LPCVD low-stress siliconnitride. This poly-Si forms the floating electrode common toboth and , as well as the gate of the sense transistor.After contact hole opening, the interconnects were realized usinga double-layer of titanium/tungsten and gold (Au).

For the back-end resonator process [Fig. 10(b)], a first layerof 0.5 m aluminum (Al) was sputtered and patterned to formthe “anti-stiction” standoff bumps. This was combined witha second layer of 2 m Al to form the sacrificial layer andthe conductive base layer to provide the current path neededfor electroplating on the isolated seed layers. The windowson which the resonator would be anchored were opened. A30 nm/100 nm titanium:tungsten/Au adhesion/seed layer wassputtered and patterned using a liftoff technique. The resonatorwas then formed by Clariant AZ 4903 photoresist molded Auelectroplating. Au was plated in a commercial Neutronex 309solution at 50 C. The respective thickness of the photoresistmold and the structural Au was 40 and 36 m. After theplating, all sacrificial layers were removed and the buried aircavity was formed in one immersion in a heated solution oftetramethylammonium hydroxide. A fabricated 5 4 arraygenerator is shown in Fig. 10(c).

V. CHARACTERIZATION

The tunnel oxide was characterized using an HP4145Bsemiconductor parameter analyzer. Typical current–voltagecharacteristics before and after electrical breakdown are shownin Fig. 11. The respective turn-on voltage needed to initiate

Fig. 12. Dependence of the floating electrode voltage V on the control gatevoltage V .

Fowler–Nordheim tunneling and the breakdown voltage are 12and 19 V, relative to an electrically grounded substrate. Thesedefine the operating range of the floating-electrode voltageat the beginning of the charging process. If duringthe charging process, then is related to the voltage appliedon the externally accessible “control gate” (i.e., the resonator)through the “coupling ratio”and the injected charge by

(12)

where was experimentally determined to be 0.6 (Fig. 12).Since prior to the charging process, a range between20–30 V was determined for . Furthermore, since electronsare the tunneling species during the charging process,and decreases with continued charging. Charging stops when

is reduced to the tunneling threshold of 12 V.Charging of the floating electrode was accomplished by the

application of a series of voltage pulses to the control gate,with an amplitude of 25 V (corresponding to an initial of

15 V) and a duration of 3 ms. The charging process can bemonitored by measuring the shift in the threshold voltage of thesense transistor, the gate of which is connected to the floatingelectrode. Since , a positive shift is expected. This isclearly observed in Fig. 13. If were reduced to 12 V suchthat the floating electrode were fully charged, would be

C/m .Power generation was characterized by mounting the micro-

generator on an MB Dynamics Model BM 25 A shaker as avibration source. With the shaker vibrating at an amplitude of2.2 m, the frequency dependence (Fig. 14) of the voltage wave-form generated across an M is monitored. A max-imum output power of 16 nW is obtained with the shaker vi-brating at 4.2 kHz, close to the designed mechanical naturalfrequency. The corresponding voltage waveform is shown inFig. 15.

Stronger nonlinearity set in and distortion in the waveform(Fig. 16) appeared when the vibration amplitude of the shaker


Fig. 13. Evolution of the transfer characteristics of a sensing transistor after aseries of electron injection pulses.

Fig. 14. Dependence of measured power output on the driving frequency.

Fig. 15. Voltage waveform of a generator driven at its natural vibration fre-quency.

was increased to 3.2 m. This distortion is a reflection of theinherent nonlinearity of the system, as described earlier.

Fig. 16. Voltage waveform of a generator driven at y = 3:2 �m.

Fig. 17. Power output dependence on resistance load R .

With the shaker vibrating at an amplitude of 2.2 m and closeto the mechanical natural vibration frequency of the microres-onator, the dependence of the output power on is shown inFig. 17. A maximum power of 65 nW is obtained at an

M , corresponding well to that simulated at the estimatedpF. The dispersion is larger for the measured than for

the simulated power output. A possible cause of such underesti-mation is the simplifying assumption of lumping the distributedgeometry of the resonator as a “point” mass in the model equa-tions, thus ignoring its internal dissipation and delay.

Compared to the first and third devices in Table I, thepresently proposed single-wafer generator is smaller and re-quires no macroassembly. Compared to the second device witha microfabricated resonator and a small capacitor gap spaceof 2.2 m, the presently proposed generator resonates at afrequency with roughly the same order of magnitude. Naturally,the actual working frequency must be tuned to each specificapplication.


VI. CONCLUSION

A single-wafer floating-electrode electrostatic electric mi-crogenerator, integrating electronic devices for “charging” andrectification, was modeled, designed, fabricated, and charac-terized. Based on the electromechanical interaction through acoupling electrostatic field, a general physical model expressedin terms of a set of nonlinear coupled differential equationsdescribing the dynamic behavior of the microgenerator wasdeveloped. For small-amplitude excitation, a circuit networkbased on a set of linearized equations is developed. The gen-erator is realized using a compatible combination of standardCMOS floating-gate process and a post-CMOS photoresistmolded electroplating process. Adequate agreement betweenmodel predictions and measurement results was obtained.

REFERENCES

[1] H. Kulah and K. Najafi, “An electromagnetic micro power generatorfor low-frequency environmental vibrations,” in Proc. MEMS 2004, pp.237–240.

[2] S. Meninger, J. O. Mur-Miranda, R. Amirtharajah, A. P. Chan-drakasan, and J. Lang, “Vibration-to-electric conversion,” IEEE Trans.VLSI Syst., vol. 9, no. 1, pp. 64–76, 2001.

[3] P. Gynne-Jones, S. P. Beeby, and N. W. White, “Toward a piezoelectricvibration-powered microgenerator,” Proc. Inst. Elect. Eng. Sci. Meas.Technol., vol. 148, no. 2, pp. 68–72, 2001.

[4] J. Boland, Y. H. Chao, Y. Suzuki, and Y. C. Tai, “Micro electret powergenerator,” in Proc. MEMS’03, Kyoto, Japan, Jan. 19–23, 2003, pp.538–541.

[5] T. Sterken, P. Fiorini, K. Baert, R. Puers, and G. Borghs, “An electret-based electrostatic �-generator,” in Proc. Transducers’03, Jun. 8–12,2003, pp. 1291–1294.

[6] Y. Arakawa, Y. Suzuki, and N. Kasagi, “Micro seismic power gener-ator using electret polymer film,” in Proc. Power MEMS 2004, Nov.28–30, 2004, pp. 187–190.

[7] T. Ma, T. Y. Man, Y. C. Chan, Y. Zohar, and M. Wong, “Design andfabrication of an integrated programmable floating-gate microphone,”in Proc. MEMS 2002, pp. 288–291.

[8] W. Ma, G. Li, Y. Zohar, and M. Wong, “Fabrication and packagingof inertia micro-switch using low-temperature photo-resist moldedmetal-electroplating technology,” Sens. Actuators A, vol. 111, pp.63–70, 2004.

[9] MATLAB, SIMULINK ver. 6.0.0.88, Release 12, The MathWorks,Inc., 2000.

[10] W. Ma, Y. Zohar, and M. Wong, “Integration of inertia micro-switcheson active substrates containing pre-fabricated electronic devices,” inProc. APCOT-MNT 2004, Sapporo, Japan, pp. 778–782, PO2-42.

[11] W. Weaver, S. Timoshenko, and D. H. Young, Vibration Problems inEngineering, 5th ed. New York: Wiley, 1990.

[12] P. C. Krause and O. Wasynczuk, Electromechanical Motion Devices.New York: McGraw-Hill, 1989.

[13] W. Ma, Y. Zohar, and M. Wong, “Design and implementation of anintegrated floating-gate electrostatic power micro-generator,” in Proc.13th Int. Conf. Solid-State Sens., Actuators Microsyst., Seoul, Korea,Jun. 5–9, 2005.

[14] S. D. Senturia, Microsystem Design. Boston, MA: Kluwer Academic,2001.

[15] H. A. C. Tilmans, “Equivalent circuit representation of electromechan-ical transducer: 1—Lumped-parameter systems,” J. Micromech. Mi-croeng., vol. 6, pp. 157–176, 1996.

Wei Ma received the B.S. and M.S. degrees fromthe University of Science and Technology of China(USTC) in 1991 and 1996, respectively, and the Ph.D.degree from the Hong Kong University of Scienceand Technology (HKUST), China, in 2005, all in me-chanical engineering. The topic of her Ph.D. disser-tation was low-temperature post-CMOS microfabri-cation and packaging technology of MEMS devices.

She was a Lecturer with USTC from 1996 to 1997and a Research Assistant working on microsensorsand actuators with HKUST and later with Nanyang

Technological University, Singapore, from 1997 to 1999. She is now a ResearchScientist with the Hong Kong Applied Science and Technology Research Insti-tute Company Ltd.

Ruiqing Zhu was born in Jiangsu, China, in 1983.She received the B.Eng. degree from the ElectronicsEngineering Department, Southeast University,China, in 2003. She is currently pursuing the M.Phil.degree in the Department of Electrical and ElectronicEngineering, Hong Kong University of Science andTechnology, China.

Her research interests are the design and fabrica-tion of micro/nanoelectromechanical systems.

Libor Rufer received the Engineer and Ph.D.degrees from Czech Technical University, Prague,Czech Republic.

Until 1993, he was with the Faculty of ElectricalEngineering, Czech Technical University. From1994 to 2003, he was an Associate Professor withJoseph Fourier University, Grenoble, France. Since2004, he has been with the National PolytechnicInstitute, Grenoble. In 1998, he joined the Microsys-tems Group, TIMA Laboratory. His expertise ismainly in radio-frequency MEMS, MEMS-based

sensors and actuators, electroacoustic and electromechanical transducersand their applications in acoustics and ultrasonics, associated measurementtechniques, and mixed-signal systems test. Currently, he is a Member of theReliable Mixed-Signal Systems Group, TIMA Laboratory.

Yitshak Zohar received the B.S. and M.S. degreesin aeronautical engineering from the Technion—Is-rael Institute of Technology, Haifa, in 1981 and 1984,respectively, and the Ph.D. degree in aerospace engi-neering from the University of Southern California(USC), Los Angeles, in 1990.

As a Research Associate at USC and the Uni-versity of California, Los Angeles (1990–1992), hebegan work on microelectromechanical systems. Hejoined the Department of Mechanical Engineering,Hong Kong University of Science and Technology,

China, as one of the founding Faculty Members in 1992, where he participatedin setting up the University Micro Fabrication Center and established theDepartment Micromachines Laboratory. At the end of 2003, he became aProfessor in the Aerospace and Mechanical Engineering Department, Uni-versity of Arizona, to develop a MEMS/bio-MEMS program and establishthe Micro/Nano Fabrication Center. His research interests are the science andtechnology of microsystems, in particular microscale fluid mechanics and heattransfer. Recently, he has started to work on Bio-MEMS subjects such as microcapillary electrophoresis, patterning multi proteins, and binding kinetics ofparticles/cells with derivatized surfaces.

Dr. Zohar is a Fellow of the American Society of Mechanical Engineers.

Man Wong (S’83–M’88–SM’00) was born in Bei-jing, China. He received the B.S. and M.S. degreesfrom the Massachusetts Institute of Technology,Cambridge, in 1983 and 1984, respectively, and thePh.D. degree from Stanford University, Stanford,CA, in 1988, all in electrical engineering.

From 1985 to 1988, he was with the Center forIntegrated Systems, Stanford University, where heworked on tungsten-gate MOS technology. From1988 to 1992, he was with the SemiconductorProcess and Design Center, Texas Instruments, and

worked on the modeling and development of integrated-circuit metallizationsystems and dry/vapor surface-conditioning processes. He is currently with theDepartment of Electrical and Electronic Engineering, Hong Kong University ofScience and Technology, China. His research interests include microfabricationtechnology, device structure, and material; physics and technology of thin-filmtransistors; organic light-emitting diode display technology; and modeling andimplementation of integrated microsystems.

Dr. Wong is a member of Tau Beta Pi, Eta Kappa Nu and Sigma Xi. In 2003,he became an Honorary Guest Professor of Nankai University, Tianjin, China.

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