The role of anchor imposed motion in the failure of MEMS microphones under free fall tests

Abstract

Numerical simulations of the transient, dynamical behaviour of MEMS microphones enlighten the mechanisms leading to possible failure during guided free fall tests. In particular, the leading role of the imposed motion at the anchors for the thin silicon membrane and the holed backplate nearby are evidenced in comparison with the air over-pressure arising in the fluid region squeezed underneath a falling jig. At the end of a numerical procedure, moving from the macro-scale to the micro-scale, elastic stress waves travelling from the impact zone reach the microphone system at its anchors, where this load combines with the air-overpressure arriving there through the narrow air ducts connected with the exterior environment. It is found that several failure mechanisms can alternatively occur, involving the membrane or, more likely, the backplate, depending on the phase balance between the two loading signals. This contribution helps to move ahead with respect to a classical pass/not pass approach for guided free fall tests, and to possibly envisage new design choices.