Analysis and elimination of the ‘skip contact’ phenomenon in an inertial micro-switch for prolonging its contact time

Abstract

An array of cantilevers, which works as a buffer in an inertial micro-switch with a bridge-type compliant fixed electrode, can effectively prolong the contact time between the two electrodes. An inertial micro-switch with a bridge-type compliant fixed electrode (i.e. a beam with holes) has been designed and fabricated by surface micromachining technology. The packaged single micro-switch (3.2 × 2.1 × 1.4 mm3) has been tested and characterized in a dropping hammer system. This micro-switch has been proved to prolong the contact time of the two electrodes, compared to a conventional micro-switch using a rigid substrate as the fixed electrode. However, an undesired ‘skip contact’ phenomenon occurred in the experiment, resulting in an insufficient contact between the two electrodes. When half-sine wave shock acceleration (with 55 g amplitude) is applied to the micro-switch, two transitory contact times, 13 µs and 8 µs, are obtained in the skip contact process. To sufficiently prolong the micro-switch contact time, a further improved micro-switch with cantilevers was designed and fabricated after simulating and analyzing the dynamic contact process of the inertial micro-switch presented in this paper. The cantilevers introduced on the proof mass of the electrode work as a good buffer between the two electrodes of the micro-switch and eliminate the skip contact phenomenon. The test contact time of the improved micro-switch with cantilevers is ∼240 µs from the 55 g shock acceleration.