Research on electrical contact characterization for microelectromechanical system (MEMS) switches has been driven by the necessity to reach a high-reliability level for micro-switch applications. One of the main failure observed when aging devices with gold contacts is the increase of the electrical contact resistance. It is related to degradations of the surface topography caused by heating, adhesion forces, etc. In this paper we investigate the performance of gold and an alternative material, ruthenium, using a methodology dedicated to MEMS contacts: a nanoindenter is used to actuate mechanically the structure, providing an accurate control of the force applied and of the resulting displacement. The electrical resistance is measured by cross rods technique "four wires" to avoid any measurement of the wire access resistances. A high resolution source meter with programmed voltage compliance and micro voltmeter is used. The test vehicles are surface micromachined on silicon substrate. Dedicated tests and modelling are presented with 5 µm² square bumps under mechanical load (until 250µN) and electrical current (1mA-100mA). Analyses of contact force dependence, temperature dependence, adhesion forces, evolution of the contact area, creep behavior and topological modifications are discussed. Regarding the results, better understanding of micro-contact behavior related to the impact of current at low- to medium-power levels is obtained. Contact heating until the softening temperature is found to be the main factor leading to shift of mechanical properties of contact materials and topological modifications. Finally an enhanced stability of the bimetallic contact was demonstrated considering sensitivity to power increase.
