JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 22, NO. 2, APRIL 2013 349

NiCr MEMS Tactile Sensors Embedded inPolyimide Toward Smart Skin

Rohit Kilaru, Zeynep Çelik-Butler, Fellow, IEEE, Donald P. Butler, Senior Member, IEEE, andIsmail Erkin Gönenli, Member, IEEE

Abstract—Piezoresistive NiCr tactile sensors have been devel-oped on surface micromachined aluminum oxide membranes,embedded between two polyimide layers, i.e., one serving as asubstrate, another as a superstrate. A novel method to bond aflexible superstrate polyimide layer onto a microelectromechan-ical system tactile sensor array is presented. The piezoresistorswere connected in a half-Wheatstone bridge configuration tominimize the effects of thermal drift. Three different types ofsensor designs were fabricated and characterized to obtain thenichrome thin-film gauge factor. The experimental results werecompared with those simulated for the same conditions of mem-brane deflection. The gauge factors range between 2.2 and 7.9for sensors with a superstrate and between 1.5 and 3.2 withouta superstrate. [2012-0090]

Index Terms—Aluminum oxide, nichrome (NiCr), superstratebonding, tactile sensors.

I. INTRODUCTION

PRESSURE sensors are essential components of cardiovas-cular pressure-sensing devices, touch screens, engine man-

ifolds, fuel lines, tire pressure monitors, robot end-effectors,as well as many other systems used in industrial automation,biomedical equipment, medical diagnosis, and automotive in-dustry. Depending upon the application, with some modifica-tions, pressure sensors have been also successfully used astactile sensors.

The use of piezoresistor-based differential pressure sensorsfor tactile-sensing applications in upper limb prosthetics isthe goal of this paper. Several researchers have developedpiezoresistor-based flexible tactile sensors with linearity, forcesensitivity, and dynamic range appropriate for their particularapplications. Some of the earlier work include silicon-basedpiezoresistive and capacitive microsensors relying on the prin-ciple of force-sensing elements with diaphragms/cantilevers[1]–[3]. Advantages include linear response, low hysteresis,robust packaging, and overload tolerance. Stress sensor arrays

Manuscript received April 9, 2012; revised July 3, 2012; acceptedSeptember 17, 2012. Date of publication November 11, 2012; date of currentversion March 29, 2013. This work was supported in part by the Texas IgnitionFund grant program. Subject Editor R. R. A. Syms.

R. Kilaru was with the Electrical Engineering Department and with TheNanotechnology Research and Teaching Facility, The University of Texas atArlington, Arlington, TX 76019 USA. He is now with IBM Research, YorktownHeights, NY 10598 USA (e-mail: rohit.kilaru@mavs.uta.edu).

Z. Çelik-Butler, D. P. Butler, and I. E. Gönenli are with the ElectricalEngineering Department and with The Nanotechnology Research and TeachingFacility, The University of Texas at Arlington, Arlington, TX 76019 USA(e-mail: zbutler@uta.edu; dbutler@uta.edu).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/JMEMS.2012.2222867

have been also demonstrated measuring triaxial stress profileswith a high stress and spatial resolution comparable to the pap-illary ridges in the dermis of human skin [4]. Papakostas et al.developed a novel contact piezoresistive force-sensing mech-anism. The device was fabricated using screen-printing tech-nology to deposit semiconductor materials on polyester sheets.Force applied on the sensor sheets resulted in a change inconductance [5]. Polymer-based sensors with thin-film metalnichrome (NiCr) as the strain gauge material were reportedby Engel et al. [6], [7] and Lee et al. [8]. A low-powerartificial electronic skin has been also achieved by contact-printing parallel arrays of semiconductor nanowires to forma flexible pressure-sensor array [9]. Our group designed andfabricated polysilicon pressure sensors based on aluminum-induced crystallization for low-force applications, down to0.3 μN [10], [11].

Although piezoresistive tactile sensors do not suffer frompoling field effects like their capacitive counterparts, they dorequire a form of compensation for the temperature variationeffects. In this report, a balanced Wheatstone bridge configu-ration is utilized for this purpose, where the bridge arms aremade of two passive resistors and two active piezoresistiveelements.

One of the challenges of flexible tactile sensors has beenpackaging or encapsulation. Packaging with flexible printedcircuit boards [7], [12], elastomer coatings [4], [8], and, specif-ically, silicone layers [13], [14] has been reported. For mostcases, however, the packaging layer is thick (up to 1.6 mm hasbeen reported) and thus interferes with the sensitivity of thetactile sensor. Moreover, it is a back-end process, which is notintegrated with the microelectromechanical system (MEMS)front-end processing.

This paper reports on NiCr-based piezoresistive tactile sen-sors in a Wheatstone bridge configuration, sandwiched between40- and 5-μm-thick polyimide layers. The former serves as asubstrate, whereas the latter is the superstrate. Packaging withthe superstrate is integrated into the MEMS process flow andnot treated as a back-end process.

The superstrate here serves three purposes. First, it protectsthe sensor and the connecting circuitry. Second, it distributesthe force, converting the force sensors on the micromachinedmembrane to tactile sensors. Third, with the substrate, it allowsthe placement of the sensors on a minimal strain plane, such thatflexibility of the entire system does not damage the sensors.

To our knowledge, this is the first time a surface-micromachined flexible MEMS tactile sensor is reported, thatis placed in a polyimide.

1057-7157/$31.00 © 2012 IEEE

350 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 22, NO. 2, APRIL 2013

Fig. 1. (a) Layout for a single tactile sensor. (b) Half-Wheatstone bridgeconfiguration.

II. TACTILE SENSOR LAYOUT

The sensor structures were half-Wheatstone bridge structuresmade up of two passive resistors P1 and P2 and two activepiezoresistors A1 and A2, as shown in Fig. 1. Ideally, P1 =P2 = A1 = A2, resulting in a null voltage at the output for noload condition. However, due to mismatch introduced duringfabrication, a nonzero offset voltage Voffset is observed even forzero load for a given applied input voltage Vin. The output ofthe Wheatstone bridge after pressure application is

Voffset +ΔV =(A1 +ΔR)(A2 +ΔR)− (P1P2)

(A1 +ΔR+ P2)(A2 +ΔR+ P1)Vin (1)

where ΔR is the change of resistance in the active piezoresis-tors due to the applied load.

III. FLEXIBLE TACTILE SENSOR FABRICATION

Fig. 2 shows the steps involved in fabricating the tactilesensor. The process starts by depositing a 0.5-μm-thick Si3N4

passivation layer on a Si carrier wafer, using RF sputtering[see Fig. 2(a)]. The next layer, polyimide PI 5878 G, is usedas the flexible substrate once the devices are peeled off thecarrier wafer after completion. It was deposited by spin coatingon the Si3N4 layer, followed by curing to attain a thicknessof 40 μm [see Fig. 2(b)]. The curing temperature for thislayer is crucial as it has a large impact on the layers to bestacked. Processing this layer at the right temperature preventsit from delaminating. We found this to be 300 ◦C by trial anderror. A 0.5-μm-thick layer of Si3N4 was then RF sputteredon the flexible substrate for passivation [see Fig. 2(c)]. Next,polyimide PI 2611 was spun on and cured to serve as a 6.5-μmsacrificial layer [see Fig. 2(d)]. The following layer was themembrane on which the piezoresistors are placed. Sputterdeposition and liftoff patterning were utilized for both lay-ers. A 1.3-μm-thick aluminum oxide (Al2O3) made up themembrane, whereas 15-nm-thick nichrome (NiCr 80/20 wt%)was used as the piezoresistors [see Fig. 2(f)]. Aluminummetallization of 0.3-μm thickness was RF sputtered and pat-terned by liftoff to form a half-Wheatstone bridge configuration[see Fig. 2(g)].

Fig. 2. Fabrication process flow for the tactile sensor.

Fig. 3. Suspended membrane after ashing.

The oxidation of NiCr was observed when trying to ash thesacrificial layer beneath the active membrane region. In orderto prevent the piezoresistors from being oxidized, a passiva-tion layer of 0.1-μm-thick aluminum oxide was deposited andpatterned by liftoff. The aforementioned step leaves openingsfor ashing of the sacrificial polyimide and bond-pad regions forwire bonding and testing. The sacrificial polyimide was thenremoved by ashing, and the membranes were suspended [seeFig. 2(h)]. The finished tactile sensor is imaged in Fig. 3.

KILARU et al.: NiCr MEMS TACTILE SENSORS EMBEDDED IN POLYIMIDE TOWARD SMART SKIN 351

Fig. 4. (a) Three-dimensional model of the tactile sensor with the superstrate.(b) The die containing the flexible substrate and the sensor is placed upsidedown on the adhesive that is spin coated on the Kapton. (c) After etching thesuperstrate and the adhesive polyimide to access the bond pads.

IV. FLEXIBLE PACKAGING WITH A SUPERSTRATE

The 3-D model of the structure with the superstrate is shownin Fig. 4. In designing the superstrate, the thickness and themechanical properties of the superstrate film were considered,as well as the adhesive material used to bond the tactile sensordie to the superstrate.

A separate carrier wafer was used to bond the superstrate onthe device wafer. The superstrate film DuPont Kapton 20ENhaving a nominal thickness of 5.0 μm was placed on analuminum foil wrapped on a 4′′ Si wafer. As the superstratefilm was very thin, it conformed to the surface of the foil. Theadhesive material PI 2555, a liquid polyimide, was dispensed onthe Kapton film. The film along with the adhesive was then spincoated at 5000 r/min for 30 s to achieve a thickness of 1.5 μm.The completed tactile sensor die was then placed upside downin contact with the adhesive material on the superstrate carrierwafer [see Fig. 4(b)]. At this stage, the stack consisting of thetactile sensor die, the adhesive material, and the superstrate filmwere heat-treated at 200 ◦C for 1 h. The 3-D model of thestructure is shown in Fig. 4(a). After bonding, the top surface ofthe superstrate film was RF sputtered with aluminum oxide for athickness of 50 nm and patterned by liftoff. The patterning stepprovides access for etching the superstrate material. The etchingof the superstrate and the adhesive was performed using O2 andCF4 gases to open the bond pads for wire bonding and testing.The close-up scanning electron microscopy photograph of theopened bond pads is depicted in Fig. 4(c). Slight underetchingis visible. As a final step, the superstrate–device–substrate stackwas peeled off the carrier wafer.

The tactile sensor thus embedded between a flexible substrateand a superstrate is shown in Fig. 5. The excess polyimidematerial can be trimmed with ordinary scissors.

Fig. 5. Flexible superstrate bonded to the tactile sensor on a flexible substrate.

TABLE IMATERIALS USED FOR TACTILE SENSOR FABRICATION

V. FINITE-ELEMENT ANALYSIS RESULTS

CoventorWare was used as the computer-aided design/electronic design automation tool for simulating the responseof the flexible tactile sensors to an applied force before andafter the application of the superstrate. The materials used in thesimulations were considered to be linear, elastic, and isotropicin nature. Table I lists the Young’s moduli and Poisson’sratios for the materials used. The boundary conditions wereselected to closely mimic the experimental conditions, as shownin Fig. 6.

A. Tactile Sensor on a Flexible Substrate

The tactile sensor 3-D model was obtained by defining a 2-Dlayout file and a process file in CoventorWare. The 3-D modeleror preprocessor is used to set the boundary conditions and themesh size to emulate the fabricated device. The interface layerbetween the sacrificial polyimide and the membrane was givena fixed boundary condition. In order to simulate touch, theload was applied on to a circular patch with a fixed radius of10 μm, corresponding to the probe dimensions used duringcharacterization of the sensors. The thickness of the membranelayer was simulated at first to determine the deflection in thecavity. Mesh generation was performed by setting the meshedmodel to consist of parabolic elements. The mesh type was ex-truded bricks. Three different sensor designs with different ge-ometries were considered with varying shuttle-pad dimensions,length of bridge arms, and piezoresistor dimensions. Nonlinearanalysis of the model was performed at an optimized mesh size

352 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 22, NO. 2, APRIL 2013

Fig. 6. Simulation settings. A load patch was created to mimic the experimen-tally applied force. The free membrane was taken to be circular due to isotropicetching of the sacrificial layer The superstrate–substrate interface and all sidesurfaces were kept fixed.

for computational time while maintaining convergence. Themembrane displacement and von Mises stresses are tabulatedin Table II. In naming the devices, the following convention isused: T2-80 refers to the second tactile sensor design with ashuttle plate size of 80× 80 μm2.

B. Flexible Tactile Sensor Packaging With aFlexible Superstrate

For the tactile sensor with a superstrate, the 3-D modeler wasset up with the same configuration settings as that of the tactilesensors without the superstrate. The boundary conditions wereset to fixed on four side surfaces of the superstrate. The load wasapplied on the circular patch of radius 10 μm, which was nowimplanted in the superstrate. The same three different sensorswere simulated but, this time, with a flexible superstrate addedon top (see Table II).

Von Mises stresses for T2 and T4 sensor designs are shownin Fig. 7.

VI. SENSOR CHARACTERIZATION

A. Tactile Sensor Characterization

The sensors were characterized on an electrical test sta-tion using Agilent technologies semiconductor parameter an-

alyzer 4155C. Pseudoresistances were measured for all thefour piezoresistors. The term pseudoresistance refers to theparallel combination of a single resistor with the other threein series, which is the resistance measured between two ad-jacent nodes on a Wheatstone bridge. Individual branch re-sistances were calculated from the measured pseudoresistancevalues.

First, the offset voltage existing due to resistance mismatchwas measured with no load at varying input voltages of0.5–2 V. Then, the load was applied by means of a 10-μm probetip assembled on a micromanipulator [10]. The probe tip wasgradually positioned down to deflect the membrane completelyin the 6.5-μm cavity. The Wheatstone bridge output voltage wasagain measured with the applied full load as a function of thesame input voltage range. From the measured output voltagevalues with and without load, it is possible to obtain the changein voltage ΔV . MATLAB was used to calculate the relativeresistance change ΔR/R from (1).

The strain values for the piezoresistors were extracted usingCoventorWare. The membrane was virtually pushed down by5.1 μm (6.5-μm cavity minus the membrane thickness andpassivation) to create the experimental conditions previouslydescribed. The average strain σavg experienced by each resistorwas computed using the technique described elsewhere [15].The gauge factor (GF) was then evaluated from the simu-lated average strain and the experimentally obtained resistancechange as

GF =(ΔR/R)

σavg. (2)

The gauge factor values thus calculated are tabulated inTable II.

B. Tactile Sensor With Superstrate Characterization

After successfully bonding the superstrate to the tactile sen-sor, another set of device characterization was performed. Inthis case, a 3.6–3.9 times higher load had to be applied onthe sensor to achieve maximum deflection of the membrane.Results are calculated after obtaining the values for: ΔV ,individual resistances, ΔR/R, σavg, and GF. The results arepresented in Table II.

The change in output voltage at maximum load is plotted asa function of the applied input voltage before the applicationof the superstrate on each tactile sensor and after. For 1-Vinput bias, ΔV for devices T1, T2, and T4 are 0.56, 0.62, and0.80 mV, respectively, for the no-superstrate case, whereas it is0.48, 0.54, and 0.74 mV, respectively, for the same devices withthe superstrate. In the aforementioned two cases, for deviceswith and without a superstrate, T4 shows a higher change involtage for a given input voltage.

VII. DISCUSSION

In order to emulate the measurement conditions, the nec-essary load for maximum membrane displacement was com-puted using CoventorWare along with the maximum stress

KILARU et al.: NiCr MEMS TACTILE SENSORS EMBEDDED IN POLYIMIDE TOWARD SMART SKIN 353

TABLE IICOMPARISON OF TACTILE SENSORS WITH AND WITHOUT A SUPERSTRATE

Fig. 7. Simulated von Mises stress distribution for T2 and T4 devices. (a) and(c) Without the superstrate. (b) and (d) With the superstrate. All cases are formaximum membrane deflection.

and the average strain experienced by the piezoresistors. Fromthe obtained values and the measured resistance change, GFwas calculated using (2). It was found that 15–17 MPa hadto be applied to the membrane through a 10-μm patch toachieve a maximum stress of 2.7–3.3 GPa for sensors withouta superstrate. The pressure ranges being on the higher side, itcan be comprehended that the membrane follows a nonlineardeflection. Due to the bonding of the superstrate to the tactilesensor die, an increase in the applied pressure is seen toachieve the same membrane deflection. The values of appliedpressure now range between 58 and 63 MPa with the maximumstress on the membrane ranging between 3.0 and 4.3 GPa.The superstrate behaves like a stress absorber and thus en-ables the tactile sensor to withstand higher applied pressure.The characterization of the tactile sensors with the superstrateoffered another advantage of protecting the membranes fromphysical damage. The maximum stress of the aluminum oxidemembrane layer in both the cases is below the yield strength ofthe material, i.e., 15.4 GPa.

Typically, 2%–5% standard deviation has been observed inthe resistance values on a single Wheatstone bridge. This ispartially due the relatively thin NiCr film, which is prone tononuniformities in the sputter deposition process. Although themeasured offset voltage values for the tactile sensors are on thelower side (10–40 mV), they are present due to the dissimilarindividual resistances comprising the bridge.

The percent normalized change in resistance for the tactilesensors without the superstrate ranges from 4.34% to a maxi-mum of 6.63%. The ΔR/R% for sensors with the superstrateranges from 4.07% for device T2 to 8.05% for device T1. Thevalue of ΔR/R depends on the individual resistor geometries,which were slightly different for each bridge arm dimension,and the combination of membrane and bridge arm geome-tries, which determine the strain experienced by the piezoresis-tor. Fig. 8 shows a linear response for the output voltage withrespect to bias except for a slight nonlinearity in the high biasrange for the cases of T2 and T4 with a superstrate.

For tactile sensors without a superstrate, the gauge factorvalues ranged from 1.50 for device T1 to 3.20 for device T4,whereas the gauge factors for tactile sensors with a superstratewere between 2.20 for device-type T2 and 7.87 for deviceT4. In general, T4 displayed better sensitivity than the othertwo devices. Due to the larger membrane size of T4, for thesame membrane deflection, smaller strain was experienced bythe piezoresistors. However, the bridge arm length and thepiezoresistor length were shorter, making the resistance changestill comparable with the other devices again for the samemembrane deflection.

It should be noted that the aforementioned gauge factorsare effective values, which were indirectly computed throughaverage simulated strain and measured resistance changes. Ourresults show a variation of gauge factors from device to device.In addition, the effective gauge factor seems to go up with theapplication of the superstrate. Both of these results are devia-tions from the ideal behavior. The gauge factor ideally shouldbe independent of the device structure (but would depend on

354 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 22, NO. 2, APRIL 2013

Fig. 8. Change in output voltage with load versus Wheatstone bridge inputvoltage for (a) T1, (b) T2, and (c) T4 devices on a flexible substrate without asuperstrate and for (d) T1, (e) T2, and (f) T4 devices with a superstrate.

the material structure). Since the superstrate absorbs the stress,the strain transferred to the sensor should be less, resulting ina smaller output voltage in effect, with the same gauge factor.The average strain is the simulated average strain on the sensor.The resistance change, on the other hand, is experimentallyobtained. Such combination of experimental and computationalresults might be the cause of these discrepancies, together withsome possible experimental artifacts such as potential lateralmovement of the load applying tip, causing additional strainexperimentally, that is not taken into account in simulations.

Although NiCr films have been extensively studied [6]–[8],[16], [17], the electromechanical properties of thin (≤ 15 nm)NiCr structures remain largely unknown. Similarly, high gaugefactors, up to 4.7, were previously observed on 10-nm-thickNiCr films [18]. Moreover, it is also known that, if the metalfilm is thin enough to be in the coalescence region, the gaugefactor sharply increases, as has been reported for Pd, Au, Cufilms [19], and manganese films [20]. These high gauge factorsobserved in thin films need to be further investigated.

VIII. CONCLUSION

Tactile sensor arrays have been successfully embedded be-tween a flexible substrate and a superstrate film using nichromeas the piezoresistive element. Three different tactile sensor

designs fabricated in a polyimide with varying micromachinedmembrane and connecting bridge-arm dimensions were simu-lated and characterized. The effect of the packaging superstrateon the sensor response was investigated. Piezoresistive gaugefactors ranging from 1.50 to 7.87 were measured.

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KILARU et al.: NiCr MEMS TACTILE SENSORS EMBEDDED IN POLYIMIDE TOWARD SMART SKIN 355

Rohit Kilaru received the B.Tech. degree inelectronics and communications engineering fromSri Ramaswamy Memorial University, Tamil Nadu,India, in 2007 and the M.S. degree in electrical engi-neering from The University of Texas at Arlington,with a focus on MEMS-based mechanical sensors onflexible substrates. His thesis and research interestswere aligned to develop and emulate human tactilesensing, primarily in upper-limb prosthetics.

He was a MEMS Process Development Intern withZyvex Laboratories, working on the NanoRetina

project. Following this, he was a Reactive-Ion Etching Process Engineer withIBM’s Microelectronics Research Laboratory, developing FEOL/MOL etchprocesses. He is currently a part of the MRAM process integration team with theIBM Thomas J. Watson Research Center, Yorktown Heights, NY. Currently, heis working on several aspects of integration to optimize and formulate efficientsemiconductor processes. His interests are in the areas of MEMS sensors,energy harvesting, and novel memory design and scaling.

Zeynep Çelik-Butler (S’84–M’87–SM’98–F’12)received dual B.S. degrees in electrical engineeringand physics from Bogaziçi University, Istanbul,Turkey, in 1982 and the M.S. and Ph.D. degreesin electrical engineering from The University ofRochester, Rochester, NY, in 1984 and 1987,respectively.

She is the Director of the Nanotechnology Re-search and Education Center and a Professor in theDepartment of Electrical Engineering at The Univer-sity of Texas at Arlington. She has served on various

IEEE committees including the IEEE International Electron Devices MeetingTechnical Committee (1988–1989), IEEE Electron Devices Society (EDS)Technical Committee on Electronic Materials (1998–2001), EDS NationalMembership Committee (1998–2006), EDS Education Awards Committee(2009–2011), and Vice Chair (2006–2009) and Chair (2010 to present) ofthe EDS North America West Regions/Chapters Subcommittee. She was aDistinguished Lecturer for EDS from 1998 to 2010. She is currently the Chairfor the EDS Chapter of Dallas and an Editor for the IEEE TRANSACTIONS ON

ELECTRON DEVICES.Dr. Çelik-Butler has received several awards including the IEEE Dallas

Section EDS Outstanding Service Awards (1995 and 1997), the IEEE EDSService Recognition Award (1995 and 2009), and the IEEE EDS DistinguishedLecturer Appreciation Award (2006). She is a Life Member of Eta Kappa Nuand a member of the American Physical Society.

Donald P. Butler (S’80–M’86–SM’98) receivedthe B.A.Sc. degree in engineering science withthe physics option from the University of Toronto,Toronto, ON, Canada, in 1980 and the M.S. andPh.D. degrees in electrical engineering from the Uni-versity of Rochester, Rochester, NY, in 1981 and1986, respectively.

He performed his graduate research at theLaboratory for Laser Energetics investigating thenonequilibrium behavior of superconductor thinfilms in response to picosecond electrical and

optical excitations. He continued his graduate research as a ResearchAssociate in 1986. In 1987, he joined the Electrical Engineering Depart-ment at Southern Methodist University as an Assistant Professor. In 1993,he was promoted to the rank of Associate Professor and Professor in 2001.He joined the Faculty of Electrical Engineering at The University of Texasat Arlington in 2002. He has published more than 160 journal articles andconference presentations and holds four patents with three additional patentspending. His current research is focused on microsensors, uncooled infrareddetectors, polymer nanocomposites, and other microelectromechanical devices.

Dr. Butler is a member of the Optical Society of America. Some examplesof his professional service include serving as Chair of the Dallas Chapter of theIEEE Electron Device Society (1988–1994), Dallas Section Chair (2001–2002),and IEEE Electron Devices Society Regions/Chapters Committee (1999–2007).He also served as the Symposium Chair for the 2001 IEEE Emerging Technolo-gies Symposium and on the organizing committee for the 2004 InternationalMicrowave Symposium as a member of the Steering Committee, Special andFocus Sessions Chair, and Webmaster. He served on the Technical ProgramCommittee for the 21st International Conference on Noise and Fluctuations(ICNF 2011). He is a recipient of the IEEE Third Millennium Medal. He wasan IEEE Electron Device Society Distinguished Lecturer (2000–2005). He wasa Topical Editor for Applied Optics/Optical Technology and Biomedical Optics(2003–2009).

Ismail Erkin Gönenli (S’08–M’10) received theB.S. degree in metallurgical and material engineer-ing from Middle East Technical University, Ankara,Turkey, in 1998, the M.S. degree in materials sci-ence and engineering from The Pennsylvania StateUniversity, University Park, in 2001, and the Ph.D.degree in electrical engineering from The Universityof Texas at Arlington in 2010. During his Ph.D.studies, he worked on design, fabrication, and char-acterization of MEMS sensors on flexible substrates.

He is a Faculty Associate with the Nanotechnol-ogy Research and Teaching Center at the University of Texas at Arlington.