Multiscale Contact Resistance Modeling of Ohmic MEMS Relays

The electrical contact resistance of electrostatically actuated ohmic contact type MEMS relays has been investigated. Multi-contact MEMS relays using electrostatic comb-drive actuators have been used to obtain experimental data in this study. The electrical contact resistances versus various applied voltages and thus loads have been studied. For an applied DC bias voltage of 172 V, the movable fingers make contact with the fixed fingers. The resistance versus applied voltage characteristics has been measured for an applied DC bias voltage in the range of 172 V to 220 V. This results in a predicted load on the surfaces between 1.32 μN and 2.95 μN. A new multi-scale rough surface contact model was used to estimate the real area of contact and electrical contact resistance as functions of the applied force for these devices. Neglecting mechanisms such as adhesion, the multiscale model appears to over predict the electrical contact resistance. Thus the roles of dry adhesion, liquid meniscus adhesion, and scale dependant material properties are considered. The results suggest that liquid meniscus adhesion and scale-dependant properties play a more significant role than dry adhesion in governing the electrical contact resistance. When these effects are considered, the predicted electrical resistance from the theoretical model appeared to match the measured resistance values fairly well, and without the use of any fitting parameters.