Multi-Physical Characterization of Micro-Contact Materials for MEMS Switches

A systematic comparison between several pairs of contact materials based on an innovative methodology early developed at NOVA MEMS is hereby presented. The technique exploits a commercial nanoindenter coupled with electrical measurements, and test vehicles specially designed in order to investigate the underlying physics driving the surface-related failure modes. The study provides a comprehensive understanding of micro-contact behavior with respect to the impact of low- to medium levels of electrical current. The decrease of the contact resistance, when the contact force increases, is measured for contact pairs of soft material (Au/Au contact), harder materials (Ru/Ru and Rh/Rh contacts) and mixed configuration (Au/Ru and Au/M contacts). The contact temperatures have been calculated and compared to the theoretical values of softening temperature for each couple of contact materials. This threshold temperature is reached for gold, ruthenium and rhodium material, with different levels of current intensity. In spite of that, no softening behavior has been observed for mixed contact at the theoretical softening temperature of both materials. Hence, considering the sensitivity to power handling and the related failure mechanisms, namely the contact adhesion, the enhanced resilience of the bimetallic contacts Au/Ru and Au/M was demonstrated. Finally focusing on the temperature distribution around the hottest levels on the surface contact interface, these results have been theoretically investigated.