Implementation of Piezoelectric MEMS Microphone for Sensitivity and Sensing Range Enhancement

This study designs and realizes an improved piezoelectric MEMS microphone with four triangular-cantilevers (Fig. 1) on a commercial 8-inch wafer. As compared with the reference design [1], this study exhibits two merits: (1) special boundary and structure design of the triangular-cantilever for sensitivity enhancement (Fig. 1a); (2) two-stage etching to successively define PZT/electrode and device-Si layers to enable the fabrication of small gaps between triangular-cantilevers for low frequency acoustic sensing enhancement (Fig. 1b). Moreover, the bottom of MEMS microphone chip is bonded (surface mount) on LGA (land-grid-array) for better acoustic performance (Fig. 1c). Preliminary FEM evaluations show the enhancement of proposed type as compare with a reference type (Fig. 2). Measurements indicate the packaged microphone of $1080\ \mu\mathrm{m}$ cavity size: acoustic sensitivity is - 37.54dBV/Pa at 1kHz; ±3dB bandwidth ranges 150Hz to 9.5kHz; noise floor of 20Hz∼20kHz bandwidth and A-weighting is −86.4dBV(A); SNR is 48.9dB(A); measured capacitance of sensing electrode is 410pF at 1kHz; dielectric constant is 250; and loss tangent of PZT is 0.015.