Contact resistance in flat thin films

Abstract

MEMS-fabricated electrical contacts are commonly used in MEMS relays. These electrical contacts can be as simple as two flat surfaces coming into contact [1]. Modeling their contact force/resistance relationship can be difficult because much of the theory on contact resistance was developed for macro-scale contacts [2], and contact properties for MEMS-scale contacts do not always agree with those predicted by this theory [3]. One contribution to this disagreement is that when the dimensions of the contact thickness are on the order of the a-spot dimensions, the spreading resistance is affected [4]. In order to determine the relationship between contact force and resistance for a wide range of parameters, we have developed a two-coupon test system which allows the properties of these contacts to be empirically determined. The design of the two-coupon system allows for the rapid fabrication of multiple contact materials and geometries. The two-coupon system was used to test the contact resistance properties of sputtered and electroplated Au films in thicknesses of 0.1 μm, 0.3 μm, and 0.5 μm. Contact force was measured using a custom flexural force gauge and the 4-point contact resistance was measured using an integrated Kelvin Structure [5]. The results are compared to traditional Holm theory to determine the effects of film thickness on spreading resistance.