An improved SPM-based contact tester for the study of microcontacts

An improved scanning probe microscope based contact tester has been designed, constructed and used for cyclic testing of various metal contacts. The tester is designed for contact material evaluation, especially for metal-contact MEMS switch applications, and is capable of simultaneous measurements of contact force and resistance. The tester uses a specially designed silicon force sensor with an integrated contact bump and a mating silicon pillar in order to simulate switch operation. The sensor and the pillar are coated with contact materials, allowing a wide range of contact metals and metal pairs to be evaluated. The testing takes place within a custom-built test chamber in which both plasma and UV-ozone treatments are available for contact cleaning and surface modification. It was found that a dissimilar contact pair of Au–Ru with O2 plasma cleaning can provide low contact adhesion and low resistance as compared with Au, Ru and Ir contact pairs. Layered structures with a thin layer of Ru on top of Au were also modeled and tested. Ru layers between 50 and 100 nm were effective in reducing adhesion and contact resistance provided the contact force is greater than 300 µN.