Multi-physics modeling and experimental investigation of low -force MEMS switch contact behavior.

MEMS ohmic contact switches offer tremendous performance compared to solid-state switches. However, their reliability and power handling capability are poor by comparison. Analysis of their failure mechanisms shows that their contact behavior is still poorly understood. Although metal contacts have been the subject of extensive research, few studies have performed tests using the low contact forces available in MEMS. For example, no studies have explored the contact heating of MEMS switches, yet some papers suggest it is beneficial and others that it may cause failure. Similarly, while contact sticking has been reported as a consistent failure mode, no study has experimentally explored MEMS contact adhesion. This dissertation presents multi-physics modeling and significant experimental data exploring the heating and adhesion of low-force MEMS contacts. We develop multiphysics models describing electrical, thermal, and mechanical behavior of MEMS switches. We also study the effects of contact force and contact heating on the contact resistance, and we present substantial data describing the MEMS contact adhesion. Using the models and experiments, we show that heating of a contact causes contact resistance to decrease. We also show that classical contact theory over-predicts contact heating for low-force contacts. A new theory is therefore developed that describes the observed behavior well. Further, we show that contact heating can be used to keep contact resistance low, avoiding one of the significant failure modes for MEMS switches. However, the data demonstrate that increasing the contact force has a much smaller effect on the contact resistance by comparison, contrary to the conventional wisdom on resistance control. Contact opening time is strongly affected by contact adhesion. Here, we demonstrate that opening time (and thus adhesion) decreases when contact resistance or pull-apart force increase, or when the apparent contact area decreases. We present a model describing the contact opening process. We also show that beam vibrations have a strong effect on reducing the contact opening time. The dissertation ends by making recommendations to improve the design and operation of MEMS switches based on the improved understanding gained from the modeling and experiments. These recommendations address the dominant failure mechanisms for MEMS switches.PhDApplied SciencesElectrical engineeringMechanical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/124700/2/3150227.pd