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Sensors and Actuators A 188 (2012) 374– 382

Contents lists available at SciVerse ScienceDirect

Sensors and Actuators A: Physical

j ourna l h o me pa ge: www.elsev ier .com/ locate /sna

eneration of sidewall patterns in microchannels via strain-recoveryeformations of polystyrene

nirban Chakraborty, Xinchuan Liu, Cheng Luo ∗

epartment of Mechanical and Aerospace Engineering, University of Texas, Arlington, TX 76019, USA

r t i c l e i n f o

rticle history:vailable online 17 December 2011

eywords:hape-memory polymeridewall patterns-D circuit

a b s t r a c t

In this work we have developed a simple approach to generate micropatterns on the sidewalls ofpolystyrene (PS) microchannels. The PS used is a thermal shape-memory polymer. The sidewall patternswere produced based on large strain-recovery property of this polymer. During the strain recovery, a shal-low, wide channel became a deep, narrow channel. In the meanwhile, micropatterns that pre-existed onthe slightly sloped sidewalls of the shallow channels were transferred to approximately vertically ori-ented sidewalls of the deep channels. A simple mathematical relationship was proposed to determine the

icrofabricationnew orientations of the channel sidewalls after the strain recovery. This relationship was further validatedby experiments. The developed approach has been successfully applied to generate Ag 50 �m × 50 �mdots, 100- and 500 �m-wide straight lines, and 150 �m-wide serpentine lines not only on the bottomsbut also on the sidewalls of PS microchannels. Furthermore, the generation of a simple conductor acrossa channel was explored. This conductor included external wires, contact pads and Ag lines. The fabricated

tially

conductor could be poten

. Introduction

Current microsystems primarily have a planar form [1,2]. Onhe other hand, sidewalls of these microsystems have not been wellsed in constructing devices. When patterns are generated on theseidewalls, they could be potentially used as electronic componentsf 3-D circuits or vertical interconnects.

Existing photolithographic approaches, such as ultra-violetUV), electron-beam, X-ray, and ion-beam, employ vertical lightxposure to transfer patterns. They are not capable of patterning theidewalls of substrate structures. Accordingly, a number of uncon-entional approaches have been developed to generate patterns onhe sidewalls using inclined UV lithography [3–5], photoresist pat-erns pre-defined in the cavities [6], shadow-masking approach [7],

odified hot-embossing approaches [8,9] or folding of suspendedlates around movable connectors [10–17]. Three types of patternsay be needed on sidewalls to create a 3-D circuit: dots, vertical

ines and horizontal lines. However, as commented in Ref. [18], theforementioned unconventional approaches are limited to createne or two types of the needed patterns on the sidewalls. There-ore, in Ref. [18], we developed an approach that was capable of

enerating any of the three types of patterns on the four outsidealls of a mm-scale PS block. The PS used was a thermal shape-emory polymer (SMP) [19], and had capability to recover from

∗ Corresponding author. Tel.: +1 817 272 7366; fax: +1 817 272 5010.E-mail address: chengluo@uta.edu (C. Luo).

924-4247/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.sna.2011.12.019

applied to create a 3-D electrical field inside the channel.© 2011 Elsevier B.V. All rights reserved.

its deformed shape to original shape upon heating to above itsglass-transition temperature (Tg). The SMPs have been employedby other researchers to fabricate, for example, high-aspect-ratiomicropillars [20], microfluidic channels [21], microreservoirs [22]and nanowrinkles [23–25]. In this work, motivated by the ideapresented in Ref. [21], we developed a new approach to fabri-cate patterns on the sidewalls of an array of microchannels basedon the large strain-recovery property of the PS film. In Ref. [21],deep, narrow channels were produced from shallow, wide chan-nels after strain recovery of pre-stretched PS films. Accordingly, ifmetal patterns were placed on these shallow channels, then someof the patterns should be transferred to the approximately ver-tical sidewalls of the deep channels. This gave a new method togenerate patterns on the channel sidewalls, and was particularlyinvestigated in this work. The metal dots and lines generated onthe channel sidewalls, as well as at the channel bottom, could bepotentially applied to produce 3-D electrical or thermal fields forthe purpose of controlling liquid flows inside the channels.

The outline of this paper is as follows. Fabrication procedure isintroduced in Section 2. Experimental results are presented and dis-cussed in Section 3. Finally, this work is summarized and concludedin Section 4.

2. Fabrication procedure

As shown in Fig. 1(a)–(d), the fabrication procedure in thenew approach is divided into three basic steps: generate shal-low channels on a pre-stretched PS film, create metal patterns on

A. Chakraborty et al. / Sensors and Actuators A 188 (2012) 374– 382 375

Fig. 1. Fabrication procedure to generate micropatterns on the sidewalls and bottom of channels etched in a mm-scale PS block: (a) shallow, wide channels are etched insidethe PS block using a stencil as a mask; (b) after removal of the stencil, the channels are revealed; (c) Ag micropatterns are produced on the substrate using another stencil asa sferrew

tticpPsatrarifi

mask; and (d) after strain recovery of the PS block, the Ag micropatterns are tranith Ag microlines and microdots.

hese channels, and produce microchannels with sidewall patternshrough strain-recovery deformations of the PS. The PS sheet testedn this work is a commercial product used for packaging appli-ations (Multi Plastics Incorporate). It is expected to have similarroperties as the one used in Ref. [19]. As indicated in Ref. [19], theS had been processed into the present form in its manufacturingite by heating a PS sheet to a temperature a few degrees below Tg

nd stretching the sheet into a film along two perpendicular direc-ions [19]. The degree of shrinking approximately equals the drawatio of the orientation process. In this work, the PS sheet was useds received. Its Tg and melting temperature were 95 ◦C and 270 ◦C,

espectively. The recovery temperature used was 145 ◦C. Accord-ng to our tests on mm-scale rectangular blocks, which were cut offrom the PS sheets, after recovery a pre-stretched PS block reducedts two lateral dimensions by factors of 4.4 and 4.0, respectively,

d to the channel sidewalls. (e) 3-D visualizations of resulting PS channels covered

implying that the pre-strains along the lateral directions were inthe range of 4.0–4.4. The recovered PS block increased the heightby a factor of 20.7.

In the first fabrication step (Fig. 1(a)), a mm-scale block was cutoff from a PS sheet and placed on a teflon-coated glass slide. Theglass slide was 75 mm long, 25 mm wide and 1 mm thick (FisherScientific Company). Subsequently, shallow channels were gener-ated on a mm-scale PS block using oxygen reactive ion etch (RIE)as follows (Fig. 1(a) and (b)). A stencil with hollow structures wasplaced on the top surface of the PS block. Subsequently, part of thePS located underneath the hollow structures was partially etched

by the oxygen RIE using the stencil as a mask. After that, the stencilwas removed and an array of shallow channels was left on the topsurface of the PS block. The oxygen RIE was conducted in a com-mercial machine (Model: Plasma Lab RIE, Plasma Technology Inc.).

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76 A. Chakraborty et al. / Sensors a

ressure was maintained at 77 mTorr, and the RF power was at05 W. The resulting etch rate of the PS was around 0.2 �m min−1.he oxygen RIE technique has been previously applied, for example,n Ref. [20] to generate cavities in a PS film. It was also employedn Ref. [26] to remove undesired PS films.

UV lithography and hot-embossing approaches are oftenpplied to generate patterns in polymers. However, PS can be dis-olved by some chemicals commonly used in the UV lithography,uch as acetone and positive photoresist (for example, S1813),hile high temperature involved in the hot-embossing process,hich is usually above Tg of the PS, may induce undesired strain

ecovery. Hence, neither approach is applicable to fabricate theesired channels in our case. Also, the channels may be generatedanually using a needle or blazer [21]. Nevertheless, due to manual

ature, it is difficult to precisely control the sizes of the channels.In the second step (Fig. 1(c)), Ag patterns were deposited on

he mm-scale PS block with the aid of another stencil. This sten-il was placed on top of the channel-formed PS block. A Ag film,hose thickness was in the range of 50–600 nm, was coated on the

lock by sputtering deposition. After sputtering, the stencil wasemoved and Ag patterns were left on the top surface, as well as onhe sidewalls and bottoms of the channels.

The channels generated out of the first step were shallow andad slightly sloped sidewalls due to two concerns. First, it saved

abrication effort and time. Second, the inclination of the chan-el sidewalls should be small. Otherwise, there was a large gapetween the stencil and the channel sidewalls. This would makeg patterns generated at the bottom of the sidewall larger than theorresponding patterns on the stencil [27]. After sputtering, thetencil was removed and Ag patterns were left on the top surface,s well as on the sidewalls and bottoms of the channels.

In the third step (Fig. 1(d)), the slope of the sidewall increasedue to the decrease in width and increase in depth of the channel,hich were caused by the strain recovery of the pre-stretched PSlm at 145 ◦C. As such, the Ag micropatterns could be generatedn both bottoms and approximately vertical sidewalls of channels.ig. 1(e) gives 3-D layouts of the dots and lines generated on the PSlocks after strain recovery. Teflon-coated glass slides were used ashe substrates for these PS blocks. Teflon is a material of low surfacenergy. It was coated on the glass substrate to avoid the adhesionetween a PS block and its glass substrate. Accordingly, during theecovery process of the PS block, we did not observe any stictionetween this block and its substrate, and the recovery deformationsf the PS block were not affected by the substrate. After fabrication,he PS block was manually removed from its glass substrate.

. Experimental results and discussions

.1. Generation of shallow, wide channels

Fig. 2 gives cross-sectional views of two representative chan-els before and after strain recovery of the PS block. Before strainecovery, the first channel was 342 �m wide and 12.5 �m deepFig. 2(a1) and (a2)). The channel sidewall had an inclination of 16◦,hile the channel bottom was relatively flat. After the strain recov-

ry, the channel became deep and narrow. It was 111 �m wide and71 �m deep, and its sidewall had an inclination of 85◦ (Fig. 2(a3)nd (a4)). The second channel experienced similar deformationsfter strain recovery. It was 583 �m wide and 18 �m deep beforeecovery (Fig. 2(b1) and (b2)). The channel sidewall had an inclina-ion of 17◦, and the channel bottom was also relatively flat. After

he strain recovery, the channel became deep and narrow as well.t was 182 �m wide and 388 �m deep, and its sidewall had an incli-ation of 85◦ (Fig. 2(b3) and (b4)). These results indicate that deep,arrow channels could be produced from shallow, wide channels

tuators A 188 (2012) 374– 382

as expected. Fig. 3(a) and (b) illustrates the changes in both chan-nel dimensions and sidewall inclination after strain recovery of apre-stretched PS film. Suppose the channel sidewall forms an angleof �i with the channel bottom before recovery (Fig. 3(a)). Let aand b denote the depth of the channel and the horizontal widthof the inclined sidewall, respectively. Accordingly, before recovery,tan �i = a/b. After recovery, the inclination angle, height and widthbecame �f, ya and xb, respectively, where y and x denote the elonga-tion ratios along the vertical and horizontal directions, separately(Fig. 3(b)). Subsequently, �f and �i are related by

�f = tan−1[(

y

x

)tan �i

]. (1)

In this work, we desire to generate patterns on deep channelswith approximately vertical sidewalls. For this purpose, �f shouldbe as large as possible. Two points can be seen from Eq. (1). First,since the value of y/x is greater than 1 in our case, �f is larger than�i. That is, the inclined degree of the sidewall is increased after thestrain recovery. Second, the value of �f increases with the increasein the values of �i and y/x. Eq. (1) was validated by experiments. Tenchannels were considered, and their cross-sectional profiles beforeand after strain recovery were characterized. Before recovery, theirwidths ranged from 335 to 583 �m, depths varied from 3 to 18 �m,and the values of �i were in the range of 3–19◦. After recovery,their widths ranged from 90 to 182 �m, depths varied from 80 to388 �m, and the values of �f were in the range of 45–85◦. The aver-age values of y and x measured out of the ten samples were 22.7 and0.66, respectively, which were substituted into Eq. (1) for predict-ing �f. As shown in Fig. 3(c), except for one sample, experimentallymeasured �i − �f relationship (obtained out of the ten samples) hada good match with the one predicted using Eq. (1). It can also beobserved from this figure that, since the value of y/x is large (33.4),�f is much larger than �i. For example, for �i to be 3◦, �f = 63◦. If�i is above 10◦, �f is over 80◦, making the recovered channel haveapproximately vertical sidewalls.

According to the value of x, along the direction perpendicularto the channel, the PS block reduced its lateral dimension by a fac-tor of 1.5. The shrinking ratio was smaller than in the case whena PS block did not have any channels fabricated on it (as indicatedin Section 2, the reduction ratio in this case was in the range of4.0–4.4). This implies that the generation of a channel on a PS blockreleased part of lateral stresses which pre-existed in the PS block.Consequently, the degree of recovery was decreased. In the mean-while, along the vertical direction, the PS block that had a channelincreased its height by a factor of 22.7, a little higher than in thecase when a PS did not involve any channels (the ratio in this casewas 20.7). This indicates that, since the channel was shallow, theeffect of this channel on the recovery along the vertical directionwas small.

3.2. Generated channels with Ag patterns

Using the procedure illustrated in Fig. 1, we fabricated Ag linesand dots on microchannels. SU-8 is a negative photoresist. Its sten-cils were used in the fabrication of these patterns. They weregenerated using UV lithography, and released employing a dry-release approach that we developed in Ref. [28].

In our initial tests, we observed cracking of the Ag lines and van-ishing arrays of Ag dots on the sidewalls after the strain recovery(Fig. 4). The lines were 100 �m wide, and the initial depths of thechannels after RIE were 15–20 �m. After recovery, the microchan-nels were over 150 �m deep. Both defects were solved by reducing

the etch depths of the channels to 5–7 �m.

Fig. 5 shows that 500 �m-wide Ag lines spaced 500 �m(Fig. 5(a)), 100 �m-wide Ag lines spaced 700 �m (Fig. 5(b)),100 �m-wide Ag lines spaced 400 �m (Fig. 5(c)), 150 �m-wide

A. Chakraborty et al. / Sensors and Actuators A 188 (2012) 374– 382 377

F 1) Meb els. Tw ages.

ssmww

ig. 2. Cross-sectional profiles of two channels before and after recovery. (a1 and b3) Measured and (a4 and b4) SEM cross-sectional profiles of the recovered channhile those in (a3) and (b3) were obtained according to the corresponding SEM im

erpentine lines (Fig. 5(d)) and Ag microdots (Fig. 5(e)) have been

uccessfully generated on the channel sidewalls without the afore-entioned defects. The original width and depth of the channelsere 500 �m and 5–7 �m, respectively. After strain recovery, theidth and depth of the channels were changed to 150 �m and

asured and (a2 and b2) SEM cross-sectional profiles of the etched channels. (a3 andhe profiles in (a1) and (b1) were determined using a Tencor surface profilometer,

80–100 �m, respectively. On the other hand, after the recovery of

the PS, the shapes and dimensions of the patterns exhibited muchsmaller changes than the distances between the patterns. At therecovery temperature, which was above Tg of PS, the PS was soft-ened, while the Ag remained solid and was rigid. Consequently,

378 A. Chakraborty et al. / Sensors and Actuators A 188 (2012) 374– 382

F ecover

te[aAstrttsit

sW

ig. 3. Schematics of cross-sectional profiles of a channel (a) before and (b) after relationships.

he recovery stress of the PS was large enough to deform the soft-ned PS but had less effect on the Ag patterns. According to Ref.29], the recovery stresses of SMPs were normally between 0.98nd 2.94 MPa (10 and 30 kgf/cm2). However, Young’s modulus ofg is around 83 GPa. Consequently, the recovery did not have atrong impact on the shapes and dimensions of the Ag patterns. Onhe other hand, such a stress was large enough to trigger the strainecovery of the PS. In addition, the Ag patterns moved together withhe underlying PS, and the distances between the neighboring pat-erns changed. The same phenomena of approximately remaininghapes and dimensions but changing distances were also observedn our previous work [18], when Ag patterns were transferred on

he sidewalls of PS blocks at a temperature above Tg of the PS.

According to Refs. [23,25,30], wrinkles could arise in metalkins when their soft substrates had large shrinking deformations.

rinkles were found in Au films when their PDMS [30] or PS

Fig. 4. SEM images of (a) cracking of the Ag lines; and

ry. (c) Comparison of theoretically predicted and experimentally measured �i − �f

[23,25] substrates shrank. Likewise, wrinkling deformations shouldoccur on the surface of a Ag-coated PS block after strain recoveryof this PS block. According to SEM pictures (Fig. 6), the wave-lengths of the wrinkles on the 100 �m-wide Ag lines spaced 400 �mand 700 �m, 150 �m-wide serpentine lines, 500 �m-wide Ag linesspaced 500 �m, and 50 �m × 50 �m dots were in the ranges of0.2–1.4 �m, 0.2–2.7 �m, 0.1–2.4 �m, 0.6–3.1 �m, and 0.1–0.6 �m,respectively. The variations in the wavelengths indicate that thewrinkles are affected by geometric shapes and dimensions of theAg patterns. We did not observe any cracks inside these wrinkles.

The critical conditions for biaxial wrinkling may be estimated as[25]:

�c = 2�h

[4Em(1 − �p

2)3Ep(1 − �m

2)

]1/3

, (2)

(b) the vanishing dots on the channel sidewalls.

A. Chakraborty et al. / Sensors and Actuators A 188 (2012) 374– 382 379

Fig. 5. SEM images of experimental results: (a)–(d) Ag line and (e) dot patterns on channels. The three pictures in each set of results, respectively, represent the configurationb d con

�

ε

wap

efore recovery, the configuration after recovery, and close-up view of the recovere

c = 14

(4Em

1 − �m2

)1/3(

3Ep

1 − �p2

)2/3

, (3)

c =[

3Ep(1 − �m2)2

]2/3

, (4)

4Em(1 − �p )

here �c is the critical wavelength when the wrinkles begin toppear, �c is the critical compressive stress, εc is the critical com-ressive strain in the metal film, and h is the thickness of the metal

figuration.

film. Em and Ep represent Young’s modules of the metal film andits soft substrate, respectively. �m and �p are Poisson’s ratios of themetal film and its soft substrate. For Ag, Em and �m are 83 GPa and0.37, respectively. Their values for PS are 3.5 GPa and 0.45. By Eq.(2), �c = 0.9 �m. The measured wavelengths are in the same order

as this value. According to Eqs. (3) and (4), we have �c = 7.9 GPaand εc = 10%. These values give a sense of the stresses andstrains that the Ag patterns have experienced during the recoveryprocesses.

380 A. Chakraborty et al. / Sensors and Actuators A 188 (2012) 374– 382

Fig. 6. Close-up SEM images of the Ag patterns after recovery of PS: (a) 100 �m-wide line 400 �m apart; (b) 100 �m-wide line 700 �m apart; (c) 150 �m-wide serpentinel

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ine; (d) 500 �m-wide line 500 �m apart; and (e) 50 �m × 50 �m dots.

.3. Fabrication of simple conductors over channels

We further explored the possibility of developing simple con-uctors over channels. For this purpose, contact pads were neededo connect an external device with the metal lines that were gener-ted across the channels. According to our initial tests, the contactads should remain large after the strain recovery of the PS block.ubsequently, external wires could be easily fixed on these con-act pads using conductive epoxy. Based on this understanding, weesigned four 6 mm × 6 mm Ag contact pads for four 1 mm × 10 mmwidth × length) Ag lines, respectively. The space between twoeighboring lines was 2 mm. These Ag lines ran across a channel,hich was 3 �m deep, 5.5 mm wide and 22 mm long. The Ag pads

nd lines had the same thickness of 600 nm. A brass stencil of thick-ess 0.5 mm was used to deposit the Ag lines and contact pads.

his stencil was fabricated using computer-aided manufacturing.ig. 7(a) shows the channel and Ag patterns generated on a mm-cale PS block. After strain recovery, the channel deformed to be5 �m deep, 1.2 mm wide and 5 mm long, and the Ag lines were

305 �m wide and spaced 438 �m apart (Fig. 7(b) and (c)). It wasalso observed that, although Ag lines had small deformations, thefour contact pads experienced relatively large deformations. Theyhad large sizes before recovery, and did not move much with theunderneath PS during the recovery, which induced relatively largestresses in these contact pads.

After strain recovery, external wires were attached to the con-tact pads using conductive epoxy (Fig. 7(d)). The continuity of theAg lines was examined by measuring I–V curves using an Electri-cal Test Station (Model: 4155C of Agilent Company). It was foundthat the resistance of the Ag lines decreased from 3.5 � initially to0.07 � after recovery. Similar phenomena have been reported inRef. [18]. As indicated in Ref. [18], the shrinking of PS block alonglateral directions increased the cross-sectional area and decreasedthe length of the Ag lines. Accordingly, resistance was reduced.

The simple conductors formed over channels could be potentiallyapplied to form 3-D electrical fields inside the channels, affect-ing liquid flows. This application would be explored in the nearfuture.

A. Chakraborty et al. / Sensors and Actuators A 188 (2012) 374– 382 381

Fig. 7. Optical microscope images of four Ag lines (with contact pads) generated over a channel: (a) before; and (b) after recovery. Close-up (SEM) views of the Ag lines (c1)o ewallt

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ver the channel, (c2) on the left channel sidewall, and (c3) on the right channel sidhe contact pads using conductive epoxy.

. Summary and conclusion

In this work, using the large strain-recovery property of PS, we

eveloped a new approach to fabricate micropatterns on the side-alls of PS channels. This method was based on the change in

he inclination of the sidewalls before and after recovery of theS film. A mathematical relationship was established to consider

. (d) Optical microscope image of the sample after external wires were attached to

the change in sidewall orientation. It was further validated withexperimental results. The developed approach included two stages:(i) fabricate micropatterns over shallow channels that are etched

inside a PS film, and (ii) make the PS film recover to its originalshape by heating it above its Tg. This approach has been applied togenerate Ag 50 �m × 50 �m dots, 100- and 500 �m-wide-straightlines, and 150 �m-wide-serpentine lines on top, bottom and side

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82 A. Chakraborty et al. / Sensors a

urfaces of PS microchannels. There was also a defect observed dur-ng initial tests. After strain recovery, the Ag lines were broken apartnd the dot patterns vanished on the sidewalls when the depth ofhe channels was large. The defect was rectified by reducing thenitial depths of the channels. Finally, we fabricated a simple con-uctor that ran across a channel. The conductor could be potentiallypplied to create a 3-D electrical field inside the channel. In con-lusion, this work demonstrated that the developed approach hasood potential to generate 3-D patterns and circuits. In the nearuture, we would like to focus on the applications of these patternsnd circuits.

cknowledgment

This work was supported in part through NSF-CMMI-0900595nd NSF-CMMI-1030659 grants.

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Biographies

Anirban Chakraborty completed his BS degree from Sikkim Manipal University,India in 2001. He received his PhD degree from Louisiana Tech University in August2007. After his graduation, he worked at ASML Netherlands B.V. as an Applicationand Business Support Engineer until March 2009 in the area of semiconductor lithog-raphy. Since August 2009 he is pursuing a post-doctoral position at the Universityof Texas at Arlington in Mechanical and Aerospace Engineering. His research inter-ests include micro/nanofabrication using silicon, metals, conducting polymers andshape-memory polymers; soft lithography and hot embossing.

Xinchuan Liu completed his BS degree at Northwestern Polytechnical University,China in 1992. He received his MS and PhD degrees from Louisiana Tech University in2003 and 2007, respectively. He was a post-doctoral researcher in the Departmentof Mechanical and Aerospace Engineering at the University of Texas at Arlingtonfrom September 2007 to August 2010. He has been a post-doctoral scholar at theDepartment of Cell Biology & Anatomy at Medical University of South Carolinasince September 2010. His research interests include micro/nanofabrication tech-nology, soft lithography, hot-embossing processes, MEMS and BioMEMS, conductingpolymer-based devices and the applications of shape-memory polymers.

Cheng Luo received his BS degree in July 1993 from the Department of Engineer-ing Mechanics at Hunan University in China, his MS degree in May 1997 from theDepartment of Mechanical Engineering at the University of Houston, and his PhDdegree in May 2000 from the Department of Mechanical Engineering at the Uni-versity of California at Berkeley. He was a master’s student in the Department ofMechanics and Engineering Science at Beijing University in China from September1993 to April 1995. He worked as a Structural Engineer in the Structural Departmentof National Oilwell Company in Houston from June 1997 to January 1998. He was aresearch fellow in the Electronics Research Laboratory at the University of Californiaat Berkeley from July 2000 to June 2001 and in the Georgetown Advanced Electron-ics (Health Microsystems) Laboratory at Georgetown University from July 2001 toAugust 2002. He was an assistant professor in the Department of Biomedical Engi-neering and the Institute for Micromanufacturing at Louisiana Tech University from2002 to 2007 before joining UT Arlington as an associate professor in the fall of 2007.He has been a full professor since September 2011. To date, he has been combininghis mechanics background with those of micro and nanofabrication: (i) to developthree nanolithographic methods for generating sub-50 nm silicon, metal, and con-ducting polymer structures in a manner of rational control and massive production,(ii) to develop various micro/nanodevices (such as sensors, diodes and capacitors)based on these nanostructures, and (iii) to develop micro/nanoboats, which will have

promising applications in actively transporting sensors in blood vessels for diseasedetection and carrying drugs for disease treatment. He has published extensivelyin technical journals and conference proceedings, and also served as session chairand/or a program committee member in a number of international MEMS and/orNEMS conferences.