MEMS piezoelectric bionic directional sound sensor based on ZnO thin film

In view of the low sensitivity of MEMS directional sound sensor, a bionic sensitive structure has been studied using finite element method (FEM). The MEMS piezoelectric bionic directional sound sensor, based on ZnO material was prepared and evaluated. In comparison to general structural optimization, which was only capable of determining the maximum theoretical sensitivity, the work carried out in this study introduced the additional parameter of electrical energy to the MEMS system, in order to incorporate and hence investigate the effect of stray capacitance, on the actual sensitivity of the device. Through a comprehensive analysis of the theoretical sensitivity, as well as the electrical energy (the product of theoretical sensitivity and the electrical energy was taken as parameter that was optimized), the thickness of the ZnO piezoelectric layer was optimized, to achieve the maximum actual sensitivity for the sound sensor. Through optimization of the fabrication process, the MEMS bionic piezoelectric directional sound sensor was developed on a 4 mm × 4 mm × 0.5 mm chip, with a relatively low residual stress exerted on the vibration film. The test results showed that the single channel sensitivity of the MEMS piezoelectric bionic directional sound sensor reached up to a high value of 0.8 mV/Pa (without amplification, 51 dB). The sensitivity with four channels in series was about 3.2 mV/Pa, and the device exhibited good directivity, as well.