Stress analysis of circular membrane-type MEMS microphones with piezoelectric read-out

Abstract

In this study, the impact of residual tensile stress on a membrane-type piezoelectric MEMS (Micro Electromechanical Systems) microphone is investigated both theoretically by FEM (finite element method) simulations and experimentally by stress measurements, by manufacturing devices and by recording the acoustic performance. Based on these findings, a design is proposed composing of segmented electrodes which are arranged close to the silicon frame as well as on the inner part of the membrane. The MEMS microphone features an aluminum nitride layer which allows a piezoelectric read-out, and multiple metal bottom and top electrodes distributed radially and azimuthally. FEM simulations were done over a large range of different layer thicknesses, membrane radii, and tensile stress levels, which indicate the existence of a sweet-spot when targeting a maximum output signal. The data showed, that thicker membranes perform better under tensile stress than thinner membranes. Furthermore, a relation between output signal and residual stress level was established, which showed that the FEM predictions agree well with the measurement results of piezoelectric microphones.