Snapping microswitches with adjustable acceleration threshold

This paper presents the design, fabrication and testing of prestressed bimorph microbeams for applications to tunable acceleration switches. The prestressed bimorph beams are buckled due to the residual stress difference between two dissimilar films, thereby generating initial beam deflections upon fabrication. Necessary and sufficient conditions for snapping action of the deflected bimorph beam have been derived from snap-through buckling analysis. A set of SiO2/p(+)-silicon bimorph beams has been designed and fabricated in three different lengths, 800, 900 and 1000 mu m. The electrostatic snap-through voltage for each microbeam has been measured as 32, 56.3 and 76.5 V, respectively. Micromechanical properties of beam materials have been measured from on-chip test structures. It is demonstrated that the three different microswitches with a 7 mu g proof-mass can be applicable to acceleration switches, where threshold acceleration levels can be adjustable within the ranges 0-14, 0-35 and 0-47 g, respectively, under inter-electrode bias voltages of 0-76 V.