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.