Novel room-temperature first-level packaging process for microscale devices

Sensors and Actuators A 123–124 (2005) 646–654

Novel room-temperature first-level packaging process for microscale devices Wen-Yue Zhang a , Joseph P. Labukas b , Svetlana Tatic-Lucic a,∗ , Lyndon Larson c , Thirumalesh Bannuru d , Richard P. Vinci d , Gregory S. Ferguson b,d a

Sherman Fairchild Center, Electrical & Computer Engineering Department, Lehigh University (LU), Bethlehem, PA, USA b Chemistry Department, Lehigh University (LU), Bethlehem, PA, USA c Dow Corning Corporation, Midland, MI, USA d Materials Science and Engineering Department, Lehigh University (LU), Bethlehem, PA, USA Received 10 September 2004; received in revised form 24 December 2004; accepted 4 March 2005 Available online 26 April 2005

Abstract Elastomer-supported cold-welding is a novel wafer-bonding process that can be performed at room-temperature, with low applied load and without applied voltage or vacuum [W.-Y. Zhang, G.S. Ferguson, S. Tatic-Lucic, Elastomer-supported cold welding for room temperature wafer-level bonding, Technical Digest of 17th IEEE International Conference on Micro Electro Mechanical Systems (MEMS 2004), Maastricht, The Netherlands, January 25–29, 2004, pp. 741–744]. It has multiple possible applications, both for temporary and permanent encapsulation of devices. In this paper, we report on the refinement and characterization of this bonding technology. First, we demonstrate improvements when new photo-patternable spin-on silicones are used instead of polydimethylsiloxane (PDMS) as the supporting material. These new materials not only simplify the patterning processing, but also reduce roughening of the bonding surfaces and enhance bond strength. We also found that self-assembled monolayers (SAMs) could be used to reduce surface roughness of the bonding surface. The Young’s moduli of the new silicone materials were measured; this property was crucial in determining the load necessary for successful bonding. In addition, the surface reconstruction of the surface of the photo-patternable elastomers after modification with an oxygen plasma was characterized. This process was important in determining the maximum allowed idle time between performing key steps in the bonding process. © 2005 Elsevier B.V. All rights reserved. Keywords: Room-temperature first-level packaging; Elastomer-supported cold-welding; Photo-patternable spin-on silicone; Self-assembled monolayer; Nanoidentation

1. Introduction Wafer-bonding techniques are used broadly in the MEMS industry, especially in device-packaging applications. Roomtemperature bonding methods are desirable because they minimize thermal stresses in the structures and do not alter mechanical properties of already fabricated devices [2,3]. They are also very beneficial when the structural microelements are made of materials that cannot withstand high temperatures, such as polymers and hydrogels [4,5]. To address these issues, we recently demonstrated elastomer-supported ∗

Corresponding author. Tel.: +1 610 758 4522; fax: +1 610 758 4561. E-mail address: [email protected] (S. Tatic-Lucic).

0924-4247/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2005.03.008

cold-welding (ESCW) as a wafer-bonding technique at roomtemperature (25 ◦ C) and low pressure (∼3 kPa), without applied voltage or vacuum [1]. Fig. 1 shows a schematic illustration of the ESCW waferbonding system, which comprises a sandwich-type structure layered as follows: substrate/elastomer/metal/metal/elastomer/substrate. Alternatively, bonding can also be achieved with an elastomer present on only one of the substrates (silicon wafer or glass). An adhesive layer was required to enhance the adhesion between the elastomer and metal layers [1]. We envision three major types of possible application for this technique: permanent wafer-level encapsulation (non-hermetic) (Fig. 2a); temporary wafer-level encapsu-

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Fig. 1. Schematic illustration of the ESCW bonding structure (not drawn to scale).

Fig. 2. Schematic illustration of three possible ESCW applications: (a) permanent wafer-level encapsulation (non-hermetic); (b) temporary wafer-level encapsulation as protection during post-processing steps; (c) permanent encapsulation with partial post-bonding removal of the cap-wafer, which would result in metal shells surrounding the devices (hermetic). This figure is not drawn to scale.

lation as protection during post-processing steps, such as dicing (Fig. 2b); and permanent encapsulation with partial post-bonding removal of the cap-wafer, which would result in hermetic metal shells surrounding the devices (Fig. 2c). In the hermetic version of the process, only one wafer would have an elastomer during the bonding step. Only one of these three applications calls for the permanent incorporation of the elastomer in the final structure, so the standard drawbacks of using a polymer as a bonding material (such as prob-

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lems with hermeticity and inadequacy for high-temperature environments) would only be a potential concern in that case. Upon contact, elastic deformation occurs within the elastomer so that the contact zones at the metal–metal (Au–Au) interface increase in size [6]. The presence of a monolayer on one of the gold surfaces prevents the cold-welding, consistent with the inference that the mechanism of bonding involves combination of dangling bonds at the gold–gold interface [6]. Hence, the properties of the elastomer, such as its compliance and surface roughness, are critical in this research. The non-photo-patternable elastomer (Sylgard® 184, Dow Corning Corporation), which consists of primarily polydimethylsiloxane (PDMS), was used in our preliminary studies. In those studies, a temporary cap-wafer was bonded on top of a device-wafer to protect pre-released MEMS structures [1]. One difficulty in that work was patterning of the elastomer layer, which required a thin metal (aluminum) film as a dry-etching mask [7,8]. As shown in Fig. 3a, the surface of PDMS was initially smooth. After a dry-etching metal masking layer (500 nm of aluminum) was deposited on top of the PDMS by e-beam evaporation, however, the surface became wavy (Fig. 3b). Fig. 3b also shows the same pattern remaining even after wet-stripping of the metal mask. This surface roughening is presumably due to a mismatch of coefficients of thermal expansion (CTEAl ∼23 ppm/◦ C [9] and CTEPDMS ∼300 ppm/◦ C [10]). These waves result from the redistribution of thermally compressive stress that develops near the surface of the sample upon cooling from the evaporator temperature to ambient temperature. The degree of roughness depends both on the elastomer properties and the metal-deposition processing, as was previously observed and explained by others [11]. Of primary importance to our studies, this roughening also significantly decreased the bonding in cold-welded junctions. To achieve better performance in the current study, new photo-patternable, spin-on silicone materials (WL-5000 series, Dow Corning Corporation) were used.

Fig. 3. Optical microscopic image of: (a) a PDMS surface before deposition of the metal masking layer and (b) the surface of the 500-nm aluminum layer on top of the PDMS (top). The surface of the PDMS after wet-stripping the metal layer is also shown (bottom). The magnification in these original images is 400×.

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The new photo-patternable silicones differ from the original elastomer in chemical composition, which determines their mechanical properties. The chemical composition of the photo-patternable silicones is a siloxane resin dispersed in a plasticizing siloxane matrix and a carrier solvent in order to facilitate spin-coating and control of final film thickness. A film of these materials is cured thermally, though incorporation of a small amount of ultraviolet light-activated catalyst enables the negative-type photo-patternability of these materials. This catalyst system is more thermally stable than traditional acrylate- or epoxy-based cure systems. The level of the catalyst is low, thus, eliminating the need to outgas photo-cure additives or ancillary chemicals and allowing low shrinkage during cure. In addition, the catalyst is not a photogenerated acid, thereby reducing concern about corrosion by acidic residues. The resin matrix of these materials can be formulated to create a range of moduli as well, but they are generally much harder and more durable in their cured state than PDMS (Sylgard® 184). This paper presents improvements in the fabrication processing and bonding quality achieved by replacing PDMS with photo-patternable silicones. These materials offer alternatives to PDMS in its other MEMS applications as well [12–15].

2. Experimental Fabrication processes for cap-wafers were described in our previous paper [1]. In the present study, photo-patternable spin-on silicone materials (WL-5150 and WL-5350) were used instead of PDMS (Sylgard® 184) in the ESCW bonding structures. Patterning of the silicones was thereby simplified to resemble standard negative-photo-resist photolithographic processing. The photo-patternable silicone materials were warmed and degassed (∼25 ◦ C, 30 min) before spin-coating onto a 3-in. silicon wafer at various speeds. The WL-5150 material, which had a low viscosity, was spun in one step. In contrast, the WL-5350 material, which had a higher viscosity, was spun in three steps: spreading (500 rpm/10 s), spinning (500–3000 rpm/30 s) and flattening (1500 rpm/30 s). Preexposure baking (110 ◦ C, 2 min) and post-exposure baking (150 ◦ C, 2 min) were performed using conventional ovens. Films were exposed to UV radiation for 40 s using a contactmode aligner (Karl Suss MJB3) having a broadband UV source and an exposure dose of 25 mW/cm2 . During the UV exposure, a Mylar® sheet (∼25 ␮m thick) was placed between the film and the mask to avoid sticking. Mesitylene was used as a developer for puddle development. Samples were spin-rinsed with 2-propanol (IPA), and full curing was finally achieved by a hard bake (180 ◦ C, 60 min) in an oven. Deposition of adhesive layers between the silicone materials and the metal (Au) is required. First, silicone materials were treated with an oxygen plasma (Technics West Inc., PE II-A Plasma System). The treatment time was 15 s

for PDMS samples and 60 s for photo-patternable silicone samples (70 W and 500 mTorr). The adhesive layer was either a standard material that enhances adhesion, such as titanium, or a self-assembled monolayer (SAM). If titanium was used, Ti (10 nm) and Au (20 nm) layers were e-beam deposited as in our previous work [1]. Self-assembled monolayers (SAMs) were deposited using a modified literature method [16]: 200 ␮L of 3-mercaptopropyltrimethoxysilane (Gelest Inc.) were mixed with 3 g of mineral oil (Fisher Scientific) in a plastic dish. The mixture was degassed for 2 h in a vacuum desiccator. Then, the samples were placed into the desiccator, with the oxidized sides up, around the dish containing the silane/mineral oil mixture. A static vacuum (∼10 mTorr) was applied for 3 h. Afterwards, the dish was removed from the desiccator and a dynamic vacuum was applied for 1 h, which was intended to remove any excess silane. Immediately after deposition of the SAM, a thin film of Au (20 nm) was e-beam evaporated onto the samples. Bonding was achieved by making contact between two gold surfaces with small applied pressures (Table 3) for 10 min. The entire procedure was performed in a class-100 clean-room environment at room-temperature. In order to determine the maximum shelf-time before performing fabrication steps after treatment of the silicone surfaces with an oxygen plasma, advancing contact angles of water (θ a ) were measured with a Rame-Hart Model 100 goniometer and used to monitor the SAM deposition and surface-reconstruction process. All contact angles were recorded at room-temperature and each value is an average of at least six different measurements taken within 10–20 s of applying the drop of water. Control wafers, which were bare silicon wafers treated in the same way as the silicones, were used to compare the contact-angle variation caused by adsorption of contaminants from the ambient environment. Characterization of the elastic behavior of the bonding layers was performed using depth-sensing nanoindentation (Hysitron Triboscope). An entire metal (20 nm Au/10 nm Ti)/elastomer sample (i.e., half of the structure in Fig. 1) was measured rather than testing individual layers in order to model the response of the sample during the bonding process, and to avoid potential artifacts associated with adhesion between the elastomer and the indenter tip. The loading rate was 150 ␮N/s, using a conical tip with a nominal radius of curvature of 1 ␮m. The actual contact area between the tip and the sample as a function of depth was calibrated using a single crystal aluminum standard. Four measurements were made with each sample, and the results averaged. The indentation modulus and hardness of each film sample was calculated using the Oliver and Pharr method [17]. At the maximum load, Pmax , the nanoindentation hardness, HNI , was determined from: HNI =

Pmax A(hc )

(1)

where A(hc ) is the contact area. From the slope of the unloading curve a reduced modulus, Er , was measured that accounts

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for elastic recovery of the sample and the indenter itself: −1
  1 − ν2  1 − ν2  Er = (2) + E sample E indenter where E is the Young’s modulus and ν is Poisson’s ratio. With the properties of the diamond indenter known (E = 1140 GPa and ν = 0.07), the indentation modulus of the material, ENI , can be found using Eq. (3).  E  ENI = (3) 1 − ν2 sample With an estimate of Poisson’s ratio for the test material, the Young’s modulus E, can be calculated from the indentation modulus. In these studies, we assumed a Poisson’s ratio of 0.48 for all of the elastomers. This value was reported for Sylgard® 184 [11]. The roughness of the gold surfaces was characterized using atomic force microscopy (AFM, Park Scientific Instruments) and the bonding strength of the gold–gold welds was determined using a tensile (pull) tester (Instron 5567).

3. Results and discussion 3.1. The dependence of film thickness of the elastomer on the spin-coating speed The dependence of film thickness of the elastomer on the spin-coating speed is shown in Fig. 4. The thickness was measured using optical microscopy and fitted using MATLAB software [1]. 3.2. Pattern quality An example of the quality of patterned stripes using the new photo-patternable spin-on silicone material (WL-5350) is shown in Fig. 5, by scanning electron microscopy (SEM).

Fig. 5. Scanning electron microscopic (SEM) image of patterned stripes using the WL-5350 material. The white scale bar is 100 ␮m in length.

The minimum line width in the pattern shown is 40 ␮m, which was limited by the mask we used. The minimum feature size reported for this material is 15 ␮m [18]. 3.3. Characterization of hardness and tensile modulus by nanoindentation Representative nanoindentation data are shown in Fig. 6. Each data set begins at zero depth, loads to a maximum, and then unloads to a finite depth determined by the amount of plastic deformation induced. Several notable features are apparent in these curves. First, each curve shows an abrupt change in slope early in the loading segment. This change appears to be associated with fracture of the Au/Ti surface layers, so the remainder of each curve is primarily influenced by the response of the elastomer. Second, the large difference in load at a given depth indicates a difference in hardness (a combination of elastic and plastic properties in a depth-sensing measurement). This difference is quantified in Table 1: Sylgard® 184 is the softest, WL-5150 is somewhat harder and the WL-5350 is approximately an order of magnitude harder than either of the other two elastomers. Finally, the unloading slopes vary significantly, indicating large differences in stiffness (Table 1). The average reduced modulus values include both sample and indenter response, but the differences between these values and the indentation moduli (sample only) are negligible because of the enormous dis-

Table 1 Summary of mechanical properties for the various elastomers

Fig. 4. Thickness of the photo-patternable silicone elastomers as a function of spinning speed.

Materials

Sylgard® 184

WL-5150

WL-5350

Tensile modulus (MPa) Reduced modulus (MPa) Young’s modulus (MPa) Indentation hardness (MPa)

20 [9] 8.2 6.3 2.06

160 [17] 146.3 112.6 9.8

370 [17] 849.7 654.4 86.8

All values in without a reference were measured at Lehigh University.

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Fig. 6. Nanoidentation results for the three elastomer samples.

parity between the stiffness of the elastomer and that of the indenter stiffness values. The approximate values of tensile modulus shown in Table 1 are calculated from the reduced modulus for each elastomer, assuming a Poisson’s ratio of 0.48. These values are useful for comparison to the tensile moduli (i.e., Young’s moduli derived from tensile tests) reported in the manufacturers’ literature [19]. In general, the nanoindentation measurements confirm the stiffness trend expected from the tensile data, but our values indicate a larger difference between the stiffest and least stiff cases; the WL-5350 is approximately two orders of magnitude stiffer than the Sylgard® 184 under our test conditions. The lack of quantitative agreement with the tensile data might be due to differences in the test conditions, to differences in the materials themselves, or to modification of the near surface behavior during the metal deposition process [11]. Nonetheless, our indentation test is a reasonable representation of the conditions extant in the cold-welding process. The hardness and modulus data all support the conclusion that the WL5350 is significantly harder to deform than the other elastomers. 3.4. Surface reconstruction of elastomers after treatment with an oxygen plasma Before deposition of an adhesive layer between the elastomer and metal (Au), the elastomer surface was oxidized by treatment with an oxygen plasma. Before the treatment with an oxygen plasma, the contact angles (θ a ) were 118◦ and 108◦ –109◦ on PDMS and new photo-patternable elastomer samples, respectively. Immediately after the treatment, θ a was 0◦ for all samples. When polymers are heated or stored against liquids or gas, their surfaces usually reorganize to minimize interfacial free energy. Against air, non-polar polymer chains tend to move from the bulk to surface and covert the surface from hydrophilic to hydrophobic states. This process, called “thermal reconstruction”, is temperature dependent and has been found in many polymeric systems [20]. The

surface reconstruction of PDMS (Sylgard® 184) has been reported [21]. Fig. 7 shows the change of advancing contact angles of water on the silicone surfaces after treatment with an oxygen plasma and storage at room-temperature and under ambient humidity. Similar results were observed for the modified surfaces of all of the elastomers, with the new elastomers reconstructing at a slightly slower rate. To guarantee successful bonding in the cold-welding experiments, the adhesive layer deposition was preformed within 1 h after the oxygen-plasma-treatment.

3.5. Reducing roughness of the bonding surface by using a SAM as an adhesive layer between the elastomer and the metal After omitting the need for a masking metal layer by using these photo-patternable silicones, the elastomers were still roughened by the deposition of metals to be cold-welded in subsequent steps. In order to reduce surface roughness, a SAM was used as an adhesive layer for gold. To confirm the presence of the SAM prior to gold deposition, advancing contact angles of water were used to monitor its formation. Upon addition of the SAM, the contact angles (θ a ) changed from 0◦ to 45◦ for all samples. Scotch® tape adhesive tests were performed to verify resulting the SAM/gold adhesion. For the samples that had an adhesive layer, the thin Au film could not been removed by Scotch tape. In contrast, the Au film was transferred to the tape from the samples that did not have any adhesive layer. We used atomic force microscopy (AFM) to examine the roughness of the bonding surface because it is one of the most critical factors for satisfactory bonding. Fig. 8 shows an AFM image of a surface made by e-beam evaporation of Au (20 nm) on top of either titanium or a SAM on the low modulus PDMS (Sylgard® 184). The surface roughness (RMS) of the Au surface was reduced from 47.1 nm (Fig. 8a) when titanium was used as adhesive layer to 8.8 nm (Fig. 8b) when a SAM was used.

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Fig. 7. Advancing contact angles of water on silicone surfaces after treatment with an oxygen plasma and storage at the room-temperature and humidity. Contact angles were measured using buffered water (pH 7), and error bars indicate one standard deviation above and below the average. All samples had been treated for 15 s (70 W and 500 mTorr) prior to reconstruction.

Fig. 8. AFM image of a surface formed by e-beam evaporation of Au (20 nm) on top of (a) Ti (10 nm) on PDMS and (b) a SAM on PDMS.

3.6. Reducing surface roughness of the bonding surface by using higher-modulus elastomers Our experiments have confirmed that flatter bonding surfaces can be achieved by using the higher modulus elastomer (Table 2). We characterized the surface roughness of the elastomers both before and after the deposition of the Au/Ti (Table 2). The roughness of bare elastomers were almost equal (∼2 nm) for all samples. The “roughening ratio” is

defined as RMS roughness of surface after metal-deposition divided by the RMS roughness of the surface before the deposition. Each result is an average of at least four measurements distributed over samples taken from three different wafers. The method for measurement of film thickness was reported previously [1]. Fig. 9 shows AFM images of the gold surfaces prior to cold-welding (20 nm Au/10 nm Ti deposited on the elastomer layer) for Sylgard® 184, WL-5150 and WL-5350.

Table 2 Surface roughness for the various elastomers before and after metal deposition Materials

Sylgard® 184

WL-5150

WL-5350

Film thickness (␮m) Standard deviation of film thickness (␮m) RMS surface roughness of bare elastomer before the metal deposition (nm) Standard deviation of rms surface roughness before the metal deposition (nm) RMS surface roughness of Au/Ti surface deposited on the elastomers (nm) Standard deviation of rms surface roughness of Au/Ti on top of elastomers (nm) Roughening ratio (%)

50.94 0.08 2.23 1.26 47.1 0.39 2.12 × 103

45.65 0.31 2.64 0.63 24.5 0.61 930

57.83 0.46 2.59 0.22 6.7 0.57 259

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Fig. 9. AFM images of the surfaces made by e-beam evaporation of Au (20 nm)/Ti (10 nm) on top of (a) Sylgard® 184; (b) WL-5150; (c) WL-5350 films.

This time, no masking aluminum layer was deposited, so the wavy pattern is a consequence of gold/titanium deposition only. The root-mean-square (RMS) surface roughnesses of these samples were 47.1, 24.5 and 6.7 nm, respectively. As expected, these experiments showed that the stiffer elastomers (WL -5000 series) retained smoother surfaces. 3.7. Bonding parameters and bonding quality Cold-welding was accomplished by placing two goldcoated elastomers (Fig. 1) into contact. The applied loads required for successful bonding were as low as ∼6 kPa for WL-5150 samples having a total silicone thickness of ∼54 ␮m, and ∼15 kPa for WL-5350 samples having a total film thickness of ∼94 ␮m. Table 3 summarizes important materials parameters for the three elastomers studied. The applied load was obtained by weights added to the bonding pairs. These loads were much lower than that would be necessary for cold-welding without elastomeric supports, which is on the order of hundreds of MPa [22]. The required loads were, however, higher for WL-5000 samples than for

PDMS samples, presumably due to the higher modulus of the former. During tensile testing, cohesive failures occurred partically within the elastomer for all Au/Ti samples, indicating that the elastomer formed the weakest layer in those areas. The approximate percentage of fractured surface visibly covTable 3 Summary of the important materials parameters for the three elastomers Materials

Sylgard® 184

WL-5150

WL-5350

Au/Ti surface roughness (RMS) (nm) Tensile modulus (in literature) (MPa) Tensile modulus (MPa) Applied load (kPa) Tensile strength (MPa) Maximum bonding strength (cohesive) (MPa) Coefficients of thermal expansion (ppm/◦ C) Thermal conductivity (W/mK)

47.1

24.5

6.7

20 [9]

160 [17]

370 [17]

6.9 ∼3 6.2 [8] 1.15

122.9 ∼6 6.0 [17] 0.96

713.7 ∼15 10.3 [17] 2.92

300 [8]

236 [17]

211 [17]

0.17 [8]

∼0.2 [17]

∼0.2 [17]

All values in without a reference were measured at Lehigh University.

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ered by a macroscopic amount of the elastomers for Sylgard® 184 samples, WL-5150 samples and WL-5350 samples was 23%, 54% and 81%, respectively. The extent of actual gold–gold contact in the WL-5350 samples was thus apparently larger than for the others bonded at the same pressure, consistent with these samples having the flattest surfaces.

4. Conclusions We have developed a room-temperature wafer-bonding process based on elastomer-supported cold-welding. We found early in our studies that patterning of PDMS using dry-etching introduced unexpected difficulties in our bonding process. The research in this report, therefore, focused on improvements when new photo-patternable spin-on silicones were used as the supporting elastomer. With these new materials, the patterning processes have been simplified to constitute negative-type photo-lithographic processing using a common UV aligner. Thus, a metal mask is no longer required, and a metal deposition that would roughen the elastomers surface can be avoided. Surface flatness increased the actual contact of coldwelding at the Au–Au interfaces and reduced the requirement of applied load. For low-modulus samples (PDMS), the surface roughness could be reduced by using a self-assembled monolayer instead of titanium as an adhesive layer between the elastomer and the gold. However, using the photopatternable elastomers, which have significantly higher Young’s moduli, resulted in reduced roughness of the bonding surface even when using titanium as the adhesive layer. This modification could result in a simpler and cheaper fabrication process. The elastic modulus and hardness of the metal/elastomer samples were characterized using nanoindentation. The new elastomers have significantly higher moduli and hardness than PDMS, and therefore, require a higher applied load for bonding than does PDMS. However, even with this increase, the loads were still much lower than those typically required for cold-welding without an elastomer [22]. These photo-patternable elastomers may be useful in many possible applications of the ESCW technique, including permanent and temporary encapsulation-packaging of MEMS devices.

Acknowledgements The fabrication was performed in the Sherman Fairchild Center at Lehigh University. The photo-patternable spin-on silicone materials (WL-5000 series) were provided by Dow Corning Corporation. The authors are grateful to Dr. R.R. Chromik for valuable discussions on mechanical characterization. This project is funded by the Pennsylvania Infrastructure Technology Alliance (PITA), Grant No. 540445.

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Biographies Wen-Yue Zhang obtained her BS from the department of Radio Electronics, Beijing Normal University, China, in 1991. From 1995 to 1997, Zhang worked at TH-QoS Laboratory, Computer Science and Technology Department, Tsinghua University to complete her masters thesis. Zhang received her MS from University of Technology and Science, China, in 1998. Zhang was employed by Research Institute of Electrical Technology and Information and Lucent Technologies in China before her pursuing her PhD in the US. She currently is a research assistant in the Sherman Fairchild Center, Electrical and Computer Engineering Department, Lehigh University, USA. Her research interests include room-temperature wafer-bonding techniques and BioMEMS. Zhang was awarded the Byllesby Fellowship and is a student member of IEEE. Joseph P. Labukas was born in Scranton, Pennsylvania. He obtained an ACS-certified BS degree in chemistry from the University of Scranton, in 2001. While studying in Scranton, he worked part time as a researcher for Acton Technologies Inc., a small firm specializing in surface chemistry of poly(tertafluoroethylene) and related plastics. Currently, he is pursuing PhD in polymer science and engineering from Lehigh University in Bethlehem, PA. Under the mentorship of Dr. Gregory Ferguson, he is investigating surface properties and behavior of a variety of polymeric systems such as elastomeric reconstruction, elastomer-supported cold welded interfaces, clay-multilayer assembly, and the preparation of gradient surfaces. Svetlana Tatic-Lucic holds a BS from the University of Belgrade, Serbia and Montenegro, and received her PhD from the California Institute of Technology, where she was working on silicon micromachined devices for in vitro and in vivo studies of neural networks. After the graduation, she worked as a research engineer at Ford Microelectronics, Colorado Springs, CO, USA, where she focused on the next-generation MEMS sensors with the application in automotive industry. Then, she was a Consulting Engineer at Coventor Inc., where she analyzed, simulated and modeled a variety of MEMS structures, including micro-mirrors for fiberoptic communications and RF switches. She joined the faculty at Lehigh University, in 2002, where she is an assistant professor of electrical and

computer engineering. Professor Tatic-Lucic has received from Lehigh University the Alfred Noble Robinson award for the outstanding performance in service to the University and unusual promise of professional achievement. Her research interests are BioMEMS, microfabrication technology and design, packaging and reliability of microsensors. Lyndon Larson attended North Dakota State University and the University of Minnesota, where he received dual bachelor of science degrees in chemistry and chemical engineering. He has worked in a variety of R&D and process engineering roles in Dow Corning since 1995 and is currently a senior applications engineer in Dow Corning’s Electronics Application Center. Thirumalesh Bannuru was born in Hyderabad, India. He obtained the BE degree in mechanical engineering from Indian Institute of Technology (IIT) Roorkee in 1998. After that, he served Engineers India Limited (EIL), New Delhi, India, as mechanical engineer for a year. In 2001, he received the MS degree in mechanical engineering from State University of New York (SUNY) Binghamton; his thesis focused on the thermal–mechanical behavior of shape-memory alloy fiber actuated metal matrix composites. He is presently a research assistant pursuing PhD in materials science and engineering at Lehigh University. His current research includes investigation of mechanical behavior of metallic thin films for microelectronics and MEMS applications. He is a student member of ASME and MRS. Richard P. Vinci received his undergraduate degree in materials science and engineering from M.I.T. in 1988. Vinci joined Lehigh University in 1998. Prior to this appointment, he held an appointment as an acting assistant professor in the department of materials science and engineering at Stanford University, from which he received his PhD in 1994. Professor Vinci is currently director of the Mechanical Behavior Laboratory in the department of materials science and engineering, Lehigh University and his research interests are the processing and properties of thin films and small-scale metal structures, with an emphasis on mechanical behavior. Gregory S. Ferguson graduated from the College of William and Mary in Virginia with BS degrees in chemistry and philosophy. He then earned MS and PhD degrees in chemistry at Cornell University. After 2 years as an NIH post-doctoral fellow in the Chemistry Department at Harvard University, Professor Ferguson joined the faculty of Chemistry at Lehigh University. He currently holds a joint appointment in the Departments of Chemistry and of Materials Science and Engineering at Lehigh. His research interests include the surface chemistry of organic and inorganic solids, the synthesis and properties of new materials, and the relationships between these two areas.