On The Performance Enhancement of Cantilever Diaphragm Piezoelectric Microphone

Abstract

This study demonstrates the piezoelectric MEMS microphone (Fig. 1a) with cantilever diaphragms and partially removed PZT (piezoelectric layer) to increase the bandwidth (BW) without sacrificing signal-to-noise ratio (SNR). The proposed design in Fig. 1a has two major merits: (1) the figure of merit of SNR×BW is presented to evaluate the performance of microphone design, (2) based on the figure of merit, the PZT and top electrode layers are partially removed to achieve a better BW without sacrificing the SNR; and two minor merits: (1) to pattern the bottom electrode to reduce stress-induced diaphragm bending to lower the acoustic short circuit; (2) apply DC bias on PZT layer to further reduce diaphragm bending. Measurements demonstrate the SNR at 1kHz up to 77.2 dB with bandwidth up to 10kHz for proposed design, and the comparison with reference designs are summarized in Table 2. Moreover, the proposed design has a 3 dB sensitivity enhancement after applying 10 V bias on PZT.