2009 JMEMS Sen LM-Droplet RF Switch

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990 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 18, NO. 5, OCTOBER 2009

A LiquidSolid Direct Contact Low-LossRF Micro Switch

Prosenjit Sen and Chang-Jin Kim

AbstractThis paper reports the design, fabrication, and test-ing of a liquid-metal (LM) droplet-based radio-frequency mi-croelectromechanical systems (RF MEMS) shunt switch withdc-40 GHz performance. The switch demonstrates better than0.3 dB insertion loss and 20 dB isolation up to 40 GHz, achievingsignificant improvements over previous LM-based RF MEMSswitches. The improvement is attributed to use of electrowettingon dielectric (EWOD) as a new actuation mechanism, which allowsdesign optimized for RF switching. A two-droplet design is de-vised to solve the biasing problem of the actuation electrode thatwould otherwise limit the performance of a single-droplet design.The switch design uses a microframe structure to accurately posi-

tion the liquidsolid contact line while also absorbing variationsin deposited LM volumes. By sliding the liquidsolid contactline electrostatically through EWOD, the switch demonstratesbounceless switching, low switch-on time (60 s), and low powerconsumption (10 nJ per cycle). [2008-0266]

Index TermsElectrowetting on dielectric (EWOD), liquid-metal droplet, microswitch, radio-frequency microelectromechan-ical systems (RF MEMS).

I. INTRODUCTION

THE CONTACT reliability of solidsolid contacts be-comes more important for microelectromechanical sys-

tems (MEMS) switches as surface plays an increased role at

microscale. The contact degradation [1] due to arcing, welding,and material transfer, which is aggravated by contact bounce,limits the operational life of all electric switches and in a greaterdegree for MEMS switches [2]. In order to solve the contactproblems and enhance reliability, a liquid was placed at thecontact point of a surface-micromachined switch as early as1996 [3]. However, the high surface tension of liquid-metal(LM) becomes dominant in the reduced scale, making thedevelopment of microscale replicas of macroscale reed relaysdifficult. Surface-micromachined switches based on low actua-tion force mechanisms like electrostatic found their operationalspeed slowed down by the high surface forces between the

liquid and the solid [4]. Better performance was possible forlarger microswitches and through use of large force actuationmechanisms like electrothermal, which require more energy peractuation cycle [5].

Manuscript received October 29, 2008; revised July 9, 2009. First pub-lished September 11, 2009; current version published September 30, 2009.This work was supported by the DARPA HERMIT program. Subject EditorK. F. Bohringer.

The authors are with Mechanical and Aerospace Engineering Department,University of California(UCLA), Los Angeles, CA 90095 USA(e-mail: [email protected]).

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.2009.2029170

A more elegant approach in the development of an LM-based microswitch is through actuation of the LM droplet toachieve switching with no movable structures. LM dropletshave been actuated by electrothermal [6], [7], electrostatic[8], [9], and electrowetting-on-dielectric (EWOD) [10][12]methods to achieve switching. Collectively, LM microswitcheshave demonstrated no contact bounce [6], [7], [12], low switch-on time (60 s) [12], fast signal rise/fall time (5 s) [12],low contact resistance [5], long life [7], and the capabilityto handle large currents (1 A) [7]. A more comprehensive

review of LM microswitches is presented in [13]. Althoughsome of the aforementioned devices have been tested for radio-frequency (RF) performance, they have mostly been limitedto 20 GHz. Most of these switches also suffered from slowactuation speeds, leading to slow switching with latencies onthe order of 1 ms.

The first known implementation of an LM-based mi-croswitch handling RF signals reported an RF performance of40 dB isolation and 0.1 dB insertion loss up to 2 GHz [6]. Inthis implementation, an LM droplet in a microchannel filledwith deionized water was toggled by the fluidic pulse generatedby thermal bubble expansion. However, the presence of waterin the OFF-state would have severely degraded the isolation

at higher frequencies. The switch-on latency was 10 ms,and required 100 mW of power. Another thermally actuatedswitch used thermal expansion of air to break and move LMdroplets [7]. Use of air as a working fluid improved the RFperformance significantly. Better than 1 dB insertion loss and20 dB isolation were reported up to 18 GHz. In addition,reported were 0.92 ms switching latency and 10 J energyrequired per cycle. Recently, an electrostatically actuated LMcapacitive switch was reported with a 0.6 dB insertion loss ofup to 20 GHz [14]. The isolation, however, degraded to 10 dBat 15 GHz and was attributed to the slotline mode arising dueto the asymmetrical switch design. The switch-on time was

reported to be 1 ms. To avoid the toxicity, nonmercury liquidshave been explored, although, so far, with little success. AnLM alloy Galinstan was immersed in a Teflon solution for areflective switch [15], and water was used for a reflective andabsorptive switch [16]. However, the LM alloy or water wasmanually pumped to achieve switching, thus restricting its useas a microswitch. Nevertheless, better than a 1.3 dB insertionloss and a 20 dB isolation were demonstrated up to 100 GHz.Pumping of fluid also limited the expected switching time to10 ms [16].

In this paper, we design, fabricate, and evaluate an LM-basedlow-loss RF switch for dc-40 GHz operation range. First, thefeasibility of LM to function in a microswitch at RF frequencies

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SEN AND KIM: LIQUIDSOLID DIRECT CONTACT LOW-LOSS RF MICROSWITCH 991

Fig. 1. Schematic of the experiment to study LM (mercury) behavior at highfrequency. Manually placed LM droplet acts as a capacitive RF short. Contactangle and droplet curvature lead to a liquidsolid contact area smaller than theSU-8 frame dimension. The switch width is 600 m.

is assessed. Then, the LM actuation mechanism adopted isdescribed. After illustrating the problems associated with asingle-droplet switch design, a two-droplet design is proposed.After discussing the device fabrication, we report experimentaland simulation results.

II. TEST OF LM DROPLET FOR HIG H-F REQUENCY RF

For an LM droplet to perform as the RF shunt-switchingelement, it should be able to provide sufficient isolation whenshorting the signal plane to the ground plane. Despite the newpossibilities (e.g., Galinstan), mercury is the only viable optionfor an actuated submillimeter LM droplet at room temperatures.Even though mercury is not among the best conductors, with its

resistivity40 times that of gold, its conductivity is not consid-ered a main issue. For example, a 100 m wide droplet shouldprovide40 dB isolation at 40 GHz. Since most of the previousLM-based RF switch work has been limited to 20 GHz, weconducted an experimental study to reveal any unexpected be-havior and assess the suitability of mercury as an RF switchingelement up to 40 GHz. As schematically shown in Fig. 1, thetest device consisted of a 6046060 m coplanar waveguide(CPW), fabricated using 8000 gold liftoff. A thin dielectriclayer (1500 silicon nitride) over the patterned electrodesprotected the gold CPW from mercury. A 100 m tall SU-8microframe defined the switch width (600 m) and held the

LM droplet in position, while the experiment was conducted.An HP 8510C network analyzer was used to measure thescattering parameters. The device insertion loss was measuredwithout the LM droplet. An LM droplet was placed manually,and the device isolation was measured, as shown in Fig. 2.Isolation of better than 25 dB over the range of 540 GHzproves the suitability of LM at high frequencies. Since theisolation profile solely depends on switch capacitance at lowfrequencies [17], a good low-frequency fit was obtained evenwhen switch inductance was ignored. The switch capacitanceand resistance extracted from the curve fitting were 25 pF and0.225 , respectively, while the switch capacitance calculatedusing the microframe dimensions was 75 pF. The fitted capaci-

tance was smaller due to the convex curvature of the nonwettingdroplet, leading to a smaller actual contact area as outlined by

Fig. 2. Measured insertion loss (without LM) and isolation (with LM) fromtest devices shown in Fig. 1. Device capacitance is calculated to be 25 pF fromcurve fitting. Series resistance is 0.225 . A good low-frequency fit is obtainedeven when inductance is ignored.

the liquidsolid contact line in Fig. 1 than the inner area of themicroframe.

III. EWOD-BASED DROPLET ACTUATION FOR SWITCHING

Microswitches based on LM actuation have suffered mostlydue to their slow actuation speeds [13]. As the first bottleneck,switching speed has been limited by the accuracy with whichthe droplets have been deposited and positioned. We havepreviously reported that the EWOD actuation of the contact lineof an LM droplet confined by a microframe, as shown in Fig. 3,allowed a high-speed operation and demonstrated the mecha-

nism for dc applications [12]. While a microframe structure, inthis case made of SU-8, held the droplet in position with a litho-graphic accuracy, high surface tension of the LM droplet en-sured that the interface position was defined accurately withinthe microframe. Furthermore, any variation in the depositedLM volume was absorbed by the meniscus at the large backopening rather than by the meniscus at the small front opening(see Fig. 3). Any variation in the LM droplet volume due tovariation in ambient temperature will also be absorbed by theback opening keeping the front meniscus practically unaffected.By keeping the droplet meniscus at the important front openingunaffected by the volume variation of the droplet, the droplet

contact line was positioned always accurately from the signalelectrode. This means high droplet placement accuracy is notrequired and manual placement is sufficient. These featuresallowed a switch design with very small switching gaps (e.g.,10 m for 600 m diameter droplet), resulting in a fastswitching. Device failure by escape of LM droplet fromthe microframe due to vibrational and horizontal shock hasbeen evaluated in [12]. For similar device design, 16 Gstability was reported. Vibrational stability will be improvedonce device fabrication is advanced to further miniaturize thedevices.

The grounding electrode grounded the LM droplet. When apotential (100 V) was applied to the actuation electrode, the

liquidsolid contact area spread and made contact with the sig-nal electrode. The area of the signal electrode which the LM



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Fig. 3. Schematic of an EWOD-actuated confined LM droplet switch. (Left and center) The switch is in OFF-state showing the liquidsolid contact line accuratelypositioned (10 m) away from the signal electrode. (Right) Application of an electrical potential to the actuation electrode causes the liquidsolid interface tospread by EWOD, and the LM makes contact with the signal electrode (switch-on). Exemplary switch dimensions: back opening 400 m, front opening 250 m,droplet height (i.e., gap between substrate and top plate) 400 m.

Fig. 4. Schematic of the two-droplet LM RF switch. Switch design consists of two mirror-imaged microframe structures. Note that the LM droplets sit on theground planes instead of the signal electrode, eliminating signal leak path.

covers and makes contact is hereafter known as the contactregion. Using the initial regime of a fast (0.5 m/s) contact-linemotion of EWOD, 60 s of switch-on time was demonstrated.Signal rise and fall time was better than 5 s with no contactbounce, and the switch used 10 nJ of energy per cycle. It wasalso demonstrated that dielectric charging had little ill effecton the actuation mechanism for

10

5 switching cycles. We willuse the same actuation mechanism to design and demonstrate alow-loss RF microswitch.

IV. TWO-DROPLET RF SWITCH DESIGN

A natural extension of the EWOD-based dc switch designdemonstrated in [12] for an RF switch would be to place asingle droplet on the signal line of a CPW. When actuated, thedroplet would spread and make contact with the ground plane,shunting the RF signal. However, the required overlap betweenthe actuation electrode and the droplet contact area for EWODmechanism to work, as shown in Fig. 3, will create a signal leak

path at high frequencies as described in detail in [18]. Usinghigh-resistivity SiCr with surface resistivity of 1200 / has

been demonstrated as a solution for this kind of problems [19].In order to simplify fabrication, having more freedom in se-lecting the cap material and achieve lower insertion loss, a two-droplet design was developed, as schematically shown in Fig. 4.

Based on 2018020 m CPW on fused silica substrates, thedesign uses two mirror-imaged microframes, each enclosingan LM droplet placed on the ground planes of the CPW. Thedroplets are grounded through a window etched in the dielectriclayer covering the CPW, as shown in Fig. 4. Placing the dropletson the ground plane, as opposed to the case of one droplet onthe signal line, solves the problem of a signal leak through thebias lines, because there is no LM above the signal electrodewhen the droplet is not actuated. In the mean time, the actuationelectrode, which is capacitively coupled to the LM droplet, isalso grounded at RF frequencies. When the droplet is actuated,the interface spreads over to the signal electrode to makecontact, and the signal is shunt to the ground plane via theLM across the two direct contacts, i.e., signal-to-LM and LM-to-ground. Grounding the LM droplets also provides a greater

freedom in selecting the package cap material and allows use ofgrounded cap.



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Insertion loss of a switch is due to a variation of the switchimpedance from the characteristic impedance. The presence ofactuation electrodes causes a change in the gap between thesignal line and the ground planes. At first sight, it may seem thatthis discontinuity will lead to a large insertion loss. However,the actuation electrode, which is capacitively coupled to the

ground plane through the LM droplet, acts as an extensionof the ground plane at RF frequencies. To reduce losses, thesignal line of the CPW is tapered in accord with the actuationelectrode to maintain 50 impedance. This tapering minimizesthe impedance-mismatched section, as shown in Fig. 4, tothe pointed extension of signal line, where the LM dropletmakes contact with the signal line when actuated. Thus, theinsertion loss in this design is from the capacitance due to theimpedance-mismatched contact region and the LM droplet. Toavoid formation of dielectric bridges and hence minimize theireffect on insertion loss, microframe structures were positionedaway from the gaps of the CPW.

The design of the microframe and its positioning with respectto the contact region was described in [12]. In the current device(Fig. 4), the microframe is designed to be 400 m high with theopening at the back and front of 400 and 250 m, respectively.The actuation electrode length w is 250 m. At the endsof the actuation electrode (location B, as shown in Fig. 4),the gap between the actuation electrode and the signal line is20 m, forming a 2018020 m CPW. Prior to the contactregion (location C, as shown in Fig. 4), the gap between theactuation electrode and the signal line is 17 m, and the signallinewidth is tapered to 146 m to obtain a 50 1714617 mCPW. The contact region is 100 m long. However, the gapbetween the actuation electrode and the signal line is 5 m.

Using Maxwell SV from Ansoft Corporation, the capacitancedue to each contact region is approximately calculated as 6.2 fF.The 3-D shape of the droplet interface makes the calculation ofthe capacitance between the signal line and the droplet difficult.The minimum gap between the signal line and the LM interfaceis 15 m. Although the surface area of the 3-D LM dropletis larger than the contact region, most of the LM surface issignificantly farther away from the signal line. Thus, a smallercontribution to the overall switch capacitance is expected fromthe LM droplets.

V. DEVICE FABRICATION

Device fabrication, as shown in Fig. 5, starts with a 700 m-thick fused silica substrate. One-thousand-ngstrm chromiumis evaporated on the substrate and patterned lithographicallyusing a wet etchant. Eight-thousand-ngstrm silicon oxide,which isolates the bias lines (same as actuation electrode) fromthe CPW, is deposited using plasma-enhanced chemical vapordeposition (PECVD) and etched using reactive ion etching(RIE). CPW is formed by liftoff of 8000 -thick gold using200 Cr as adhesion layer. LOR-20B from MicroChem is usedwith AZ5214 from Clariant to obtain a clean liftoff of such athick metal. For the dielectric separating the actuation electrodefrom the LM, 3500 nitride is deposited using PECVD and

etched by RIE. Since most LMs including mercury attack mostmetals, a protective layer is required at the contact regions.

Fig. 5. Process flow for device fabrication. Section AA from Fig. 4 isdepicted.

Several metals (e.g., chromium, iron, platinum, nickel, andtungsten) are known to be compatible with mercury. A layer of2000 Cr/Ni is deposited at the contact regions using liftoff.To reduce hysteresis (i.e., static friction which restricts contact-line motion) and have a reasonable actuation voltage, a thinhydrophobic coating of Teflon is used. Teflon is spin coatedto obtain a 2000 film and baked at 320 C for 3 h. Furtherprocessing of Teflon-coated wafer is difficult due to the lowsurface energy of Teflon, which results in poor adhesion ofany film coated on it. To successfully coat photoresist (PR),we add surfactant to the PR. The Teflon layer is patternedlithographically and etched in oxygen plasma. After the PR isremoved in acetone, the patterned Teflon layer is baked again

at 320 C for 3 h. To allow the building of the microframein subsequent steps, the Teflon-covered area is minimized. To



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Fig. 6. (Top) Optical micrograph showing hydrophobic layer was processes (i.e., coated and patterned) before microframe fabrication. CPW is 2018020m,(green) actuation electrode is 260 m long, and signal electrode is 100 m long and 50 m wide. (Bottom) SEM of a fabricated device before LM dropletplacement.

Fig. 7. Measured profile of a current generation device with very small difference of height between the actuation electrode and the contact region.

obtain 400 m-thick microframe structures, SU-8 2150 fromMicroChem is deposited by a single spin and soft baked at95

C for 3 h. Temperature is always ramped up or down with

a rate of 60 C/hr from 50 C. A 300 s step exposure witheach step consisting of a 30 s exposure and a 20 s delay is usedto help reduce surface hardening due to heat. After a 45 minpostexposure bake, the features are developed with agitation.The Teflon layer is again baked in a nitrogen environment, butthis time at 200 C for 3 h. A lower temperature and nitro-gen environment are used to prevent SU-8 burning. Finally, a400 m-diameter mercury droplet is placed in each micro-frame manually. SEM micrographs of a fabricated device be-fore LM placement are shown in Fig. 6.

This process deviates from the usual processing practice ofcoating and patterning a Teflon layer as the last step. Such

a conventional practice protects the Teflon from any furtherchemical processing, which may degrade its quality. Following

this convention, however, is not possible for our case dueto the presence of the tall SU-8 microstructures. If Teflon iscoated over tall microstructures, the surfactant-mixed PR filmis destabilized during spin coating, leading to the dewetting ofthe PR on the Teflon. Furthermore, the capillary force causesPR to accumulate in the small spaces between the tall SU-8microstructures. Teflon is baked after every step to recover thefilm quality from any degradation during processing. Fig. 6shows the final two steps, where the Teflon is processed firstand then the SU-8 microstructures are fabricated.

Another aspect of designing the process flow is to minimizethe surface topography; the moving contact line needs to slideacross. When an electric potential is applied to the actuationelectrode, the contact line spreads over it (see Fig. 3). Thesection of contact line over the signal electrode, however, does

not see the electric field from the actuation electrode andhence feels no actuation force. Instead, the contact line over



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Fig. 8. Optical micrograph of the experimental setup. (Left) Bias tees connection to the GSG probe tips and the dc actuation probe tip. (Right) Device under testwith two LM (mercury) droplets.

the actuation electrode pulls this forceless section toward thesignal electrode. With the local loss of actuation force over thesignal electrode, the contact line is prone to pinning by anysmall surface bump as explained in detail in [18]. This problemwas identified when the previous generation devices gave acapacitive shunt response instead of the expected dc shunt. Thecurrent process, shown in Fig. 5, solves the problem of contact-

line pinning by lowering the contact region to the same level asthe actuation region, as shown in Fig. 7.

VI. SIMULATION AND TES T RESULTS

Device simulations were carried out using high frequencystructure simulator (HFSS) from Ansoft Corporation. Resistiv-ity of mercury was defined as 961 n m. SU-8 was definedas a dielectric with dielectric constant of 3.25. The shape ofthe LM droplet remains spherical and is easily defined whennot actuated. Determining the interface shape when actuated is,however, not trivial. To solve this issue, we assume a simplified

polygonal shape approximately matching the actuation elec-trode shape for the droplet interface. Although an approximateinterface shape is used, important parameters (e.g., the overlaparea at the contact region and width of the bridge betweenthe signal line and the ground plane) will vary insignificantlyfrom the true situation. An experimental setup to test the RFswitching performance is shown in Fig. 8. HP 8510C or AgilentE8361A network analyzer is used to measure the device perfor-mance. A dc signal from a National Instrument multifunctionaldata acquisition amplified using a Trek amplifier is used toactuate the switch. Ground-signal-ground (GSG) probe tipsfrom Picoprobe are used to contact the CPW. To calibrate thesetup on a wafer, thru-reflect-line calibration was performed.

The measured insertion loss is better than 0.3 dB up to40 GHz, as shown in Fig. 9 along with the simulation results,showing a good match. The return loss is given by

|S11| = CuZ02

(1)

where Cu is the switch capacitance. The switch capacitancecalculated by curve fitting the return loss is 14 fF, while switchcapacitance calculated from HFSS simulation is 18 fF. Thisdifference is due to uncertainty in the contact-line position.Contact-angle hysteresis leads to an uncertainty in the staticcontact angle, resulting in a variation of the contact line posi-

tion. A 5 variation in the contact angle will lead to a variationof 6 m in the contact-line position. This variation of the LM

Fig. 9. Device insertion loss and return loss.

Fig. 10. Device isolation.

interface position will lead to a variation in the contribution ofthe LM to the switch capacitance. With approximately 12.4 fFcontribution from the contact regions (calculated above), theLM contribution is approximately 1.6 fF measured or 5.6 fFsimulated.

The switch is actuated using 100 V, and isolation is mea-sured, as shown in Fig. 10. The switch isolation is given by

|S21| =R2 + 2L2

(R + 0.5Z0)2 + 2L2

(2)

where R and L are the switch resistance and inductance,respectively. The isolation measured is better than 20 dB up to



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40 GHz. The 5.2 pH switch inductance is obtained from thecurve fitting the simulation data. It is not possible to obtaina good match for the resistance from the simulation, as thesoftware does not account for the contact resistance, which isthe major source of the switch resistance. The switch resistanceis obtained as 1.32 by fitting to the measured isolation. The

extracted resistance of two contacts in parallel is in good accordwith the previously reported 2.35 for a single 50 m 50 mcontact [12].

VII. SUMMARY AND CONCLUSION

In this paper, a low-loss RF MEMS switch based onliquidsolid direct contact using two LM droplets has beenpresented. With 600 m in size (not including the CPW ex-tension required for testing), this switch is comparable to otherbeam-based RF MEMS switches, which are usually hundredsof micrometers in length [2]. The basic design was based onthe previously reported fast EWOD actuation of an LM droplet

in the microframe, which led to bounceless operation with60 s switch-on time, less than 5 s signal rise/fall time, andnanojoules of energy consumption per actuation cycle. Afteridentifying a problem of signal leakage at RF frequencies, atwo-droplet design has been developed to solve the biasingproblem that otherwise would degrade the RF performance andrequire deposition of a high-resistivity SiCr layer. Switch de-sign was optimized with the aim of improving RF performance.Device fabrication required special care to prevent contact-linepinning, which led to poor liquidsolid contact. The insertionloss was measured to be better than 0.3 dB and isolation betterthan 20 dB both up to 40 GHz. The fitted switch characteristics

included a 14 fF up-state capacitance and a 5.2 pH down-stateinductance. The switch contact resistance extracted from curvefitting was 1.32 , similar to the value reported previously fora dc switch.

With a liquidsolid contact, the reported switching technol-ogy is expected to lead to high-reliability RF MEMS switchesincluding contact switches. It is further expected that the useof LM droplets will allow the development of high-power hotswitching devices. There are, however, several key issues thatneed to be solved before the technology matures to deploythe devices. With contact reliability not a primary issue forthis switch, the major expected failure mechanism is throughdielectric charging. Even though dielectric charging has beendemonstrated to have little effect on the actuation mechanismup to 105 cycles [12], reliability demonstrations up to 109

cycles, or more would require hermetic packaging. Hermeticpackaging of these devices in an inert environment is a signifi-cant challenge due to the low boiling point of mercury. Galliumand its alloys (e.g., Galinstan) would allow packaging at highertemperatures, although instead they are more susceptible to sur-face oxidation. Detailed results related to hermetic packagingof liquid metal droplets and long-term device reliability will bepresented elsewhere after completion of the ongoing study.

Significant switch-to-switch contact resistance variation wasobserved, which is attributed to oxidation of the LM in air. It is

also expected that cycle-to-cycle contact resistance degradationwill happen in air due to continuous oxidation of LM. This

problem will be solved once hermetic packaging in an inertenvironment is developed for these switches. Even with switchcontact resistance of 1.32 which is comparably higher thanthe best MEMS switches [20], the LM-based switches areexpected to fare better due to no contact degradation fromarcing or welding. Simplified 2-D FEM simulation shows for

designs based on silicon substrates with adequate heat sinks ourdevices should be able to handle 1 A before mercury boilingat 357 C. These tests were not performed considering the toxicnature of mercury vapor. Galinstan which boils at 1300 Cshould be able to handle much larger currents.

ACKNOWLEDGMENT

The authors would like to thank J. Jenkins and T. Wu fortheir discussions about the project, Dr. S. Mathai and the staffof the Center for High Frequency Electronics, University ofCalifornia, Los Angeles, for their help with the RF measure-

ments, and A. Lee for her help with this paper.

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Prosenjit Sen was born in Calcutta, India, in 1978.He received the B.Tech. degree in manufacturingscience and engineering from Indian Institute ofTechnology, Kharagpur, India, in 2000 and the Ph.D.degree in mechanical engineering from the Univer-sity of California, Los Angeles (UCLA), in 2007.

He is currently with the Micro and Nano Man-ufacturing Laboratory, Department of Mechanicaland Aerospace Engineering, UCLA. His research in-terest includes microfludic systems, droplet dynam-ics, liquid-metal-based RF MEMS, and reliability of

electrowetting-on-dielectric devices.Dr. Sen was the recipient of the Institute Silver Medal from the Indian

Institute of Technology.

Chang-Jin CJ Kim received the B.S. degreefrom Seoul National University, Seoul, Korea, theM.S. degree from Iowa State University, Ames, withGraduate Research Excellence Award, and the Ph.D.degree in mechanical engineering from the Univer-sity of California, Berkeley, in 1991.

In 1993, he joined the faculty of the Universityof California, Los Angeles (UCLA), where he has

developed several MEMS courses and establisheda MEMS Ph.D. major field in the Department ofMechanical and Aerospace Engineering. Directing

the Micro and Nano Manufacturing Laboratory, UCLA, he is also active inthe commercial sector as board member, scientific advisor, and consultant.He currently serves as a Subject Editor for the IEEE/ASME J OURNAL OFMICROELECTROMECHANICAL SYSTEMS and on theEditorial Advisory Boardof the IEEJ Transactions on Electrical and Electronic Engineering. His re-search interests include MEMS and nanotechnology, including the design andfabrication of micro/nanostructures, actuators, and systems, with a focus on theuse of surface tension.

Dr. Kim has served on numerous technical program committees, includingTransducers and the IEEE MEMS Conference, and on the U.S. Army ScienceBoard as a Consultant. He is currently chairing the Devices and SystemsCommittee of the ASME Nanotechnology Institute and serving on the NationalAcademies Panel on Benchmarking the Research Competitiveness of the U.S.in Mechanical Engineering. He was the recipient of a TRW Outstanding Young

Teacher Award, National Science Foundation CAREER Award, Association forLaboratory Automation Achievement Award, Samueli Outstanding TeachingAward.

Documents

2009 JMEMS Sen LM-Droplet RF Switch