An experimental characterization of Au-, Ru-, Rh- and Ni- based microcontacts for MEMS

From several years, NOVA MEMS has developed a new set-up for the characterization of contact materials used in micro- switches. Comparisons between several pairs of contact materials have been done with this methodology using a commercial nanoindenter coupled with electrical measurements on test vehicles specially designed to investigate the underlying physics that drives the surface-related failure modes. The data provides a better understanding of micro-contact behaviour related to the impact of current at low- to medium-power levels. 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/Ni contacts). The super-temperatures of the contacts have been calculated and compared to the theoretical values of softening temperature for each material. It can be shown that this temperature can be reached for gold, ruthenium and rhodium material, with different levels of current intensity. However, no softening behaviour has been highlighted for mixed contact. An enhanced stability of the bimetallic contacts Au/Ru and Au/Ni was demonstrated considering sensitivity to power increase, related to thermo-mechanical deformations and topological modifications of the contact asperities. These results are discussed in a theoretical way by considering the temperature distribution around the hottest niveau-surface at the contact interface.