contactIEEE2007 - JOURNAL OF MICROELECTROMECHANICAL...

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JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 16, NO. 5, OCTOBER 2007 1263 Direct Contact-Area Computation for MEMS Using Real Topographic Surface Data Daniel J. Dickrell, III, Member, ASME , Michael T. Dugger, Member, ASME , Matthew A. Hamilton, and W. Gregory Sawyer, Member, ASME Abstract —Direct computation of interfacial contact area for microelectromechanical-system applications was performed nu- merically using the measured device surface topography and the material hardness to deFne the ±ow stress of an individual ele- ment. The simulation results compared well with the established contact-area determination methods and also introduced new ca- pabilities that enabled the visualization of the spatial distribution of contact spots to be computationally mapped and rendered directly onto device surfaces. [2006-0276] Index Terms —Contact mechanical factors, contacts, friction. I. INTRODUCTION I NTERFACIAL contact-area determination is very important for microelectromechanical-system (MEMS) device design. The phenomena that affect the MEMS device performance and lifetime are primarily dependent on the interaction area between device surfaces (examples include surface adhesion, friction, wear, and electrical contact resistance). The gross contact geometry of most MEMS electrical switches is planar, which stems from the layered fabrication processes that are used to create the device. The actuation forces in the operation of MEMS contacts are typically on the order of 10–100 µ N. The local surface roughness mainly determines the real area of contact as very few asperity contacts are required to support these loads [1], [2]; the real area of contact is likely orders- of-magnitude smaller than the apparent area of contact, as de±ned by the device design. The combination of low con- tact forces and nominally ²at contact geometry accentuates this subtle in²uence of the surface-roughness variation on device contact-area spot size and distribution. An accurate determination of interfacial contact area in MEMS requires proper surface-roughness characterization and appropriate uses of these measurements to predict contact-area size and distri- bution under these extremely low force operating conditions. Fig. 1(a) and (b) shows the characteristic roughness exhib- ited by a MEMS device contact surface. Fig. 1(a), which is obtained by scanning electron microscopy, shows the over- Manuscript received December 13, 2006; revised April 9, 2007. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s Na- tional Nuclear Security Administration under Contract DE-AC04-94AL85000. Subject Editor L. Lin.
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contactIEEE2007 - JOURNAL OF MICROELECTROMECHANICAL...

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