Adhesion Analysis for MEMS Based on Electrical Contact Resistance Measurements

Because adhesion forces are especially important at the submicron scale, they play a dominant role in several fields of nanotechnology, such as biology, atomic force microscope (AFM) imaging, magnetic disk drives, and microelectromechanical systems (MEMS). The profound importance of adhesion forces in MEMS has been the principal theme of several studies. A common approach for measuring the surface energy is based on balancing the elastic energy stored in microcantilever beams partially adhered to substrates with the work of adhesion, assumed equal to the surface energy multiplied by the apparent area of the attached beam length. However, because the apparent contact area is significantly larger than the real contact area and the elastic energy stored in the deformed asperity microcontacts is neglected, this traditional method may greatly underestimate the interfacial adhesion energy. Consequently, the objective of this study was to develop a method for determining indirectly adhesion forces and adhesion energies form relatively simple in situ electrical contact resistance (ECR) measurements. The method presented herein is based on a theoretical treatment of the ECR encountered during contact of isotropic, conductive, rough surfaces, using multi-scale fractal description of the equivalent surface topography, constitutive contact relations for elastic-perfectly plastic asperity microcontacts, and size-dependent constriction resistance of microcontacts. Results are presented for the adhesion force and adhesion energy in terms of ECR for different surface topographies.