A micromechanical acceleration switch has been devised and fabricated utilizing the snap-through buckling behavior of a bent beam. It is tunable in the sense that threshold acceleration levels can be adjusted by inter-electrode bias voltages.
From a design analysis, necessary and sufficient conditions for a snapthrough switching function have been derived for a clamped-clamped shallow beam. The necessary condition has resulted in a geometric relation, in which the ratio of beam thickness to initial beam deflection plays a critical role in the snapping ability. The sufficient condition for the snapping action has been obtained as a function of the inertia force caused by applied acceleration, and the electrostatic force, adjustable by an inter-electrode voltage.
For experimental Investigations, a set of microbeams of $SiO_2$/$p^+$-Si bimorphs have been fabricated. Geometric size and mechanical behavior of each film have been measured from on-chip test structures. Estimated and measured characteristics of the fabricated devices are compared. Based on the electrostatic threshold voltage measured from each device, adjustable ranges of the threshold acceleration have been estimated. Some discrepancies between the estimated and the measured values have been observed, mainly caused by inaccuracies in the manufactured geometries and residual stresses.
The developed device is shown to be well usable as an acceleration switch, and applicable to a wide variety of novel micro-devices, including nonvolatile micro-memory cells, micro-valves, micro-actuators, micro-toggle switches, micro-voltmeters, and so on.
