A Sc0.096Al0.904N-Based Bimorph Piezoelectric MEMS Microphone Using 3 × 3 Circular Diaphragms

This work presents a bimorph piezoelectric microelectromechanical system microphone (b-PMM) with high receiving sensitivity and signal-to-noise ratio (SNR) based on an array of circular diaphragms in a size of 0.375$\times$3$\times$3 mm$^{\text{3}}$. The b-PMM is fabricated using Sc$_{\text{0.096}}$Al$_{\text{0.904}}$N with thicknesses of 486.56 and 478.45 nm, respectively. The lumped element model and mechanical analysis of the diaphragm array are established, and the bimorph structure shows increased sensitivity and decreased noise. Electro-acoustic measurements are presented in an anechoic test box (B&K 4232). Compared with the AlN-based b-PMM, the sensitivity and SNR of the ScAlN-based one are$-$69 dB (re: 1 V/Pa) and 58.4 dB at 1 kHz, increased by 16.4% and 3.4 dB, respectively. Besides, the measured minimum detectable pressure (MDP), resolution, and total harmonic distortion (THD) are 35.6 dB SPL, 34 dB SPL, and 0.087% at 1 kHz, respectively. The ScAlN-based b-PMM with high noise resolution will have a bright prospect in application scenarios such as intelligent voice acquisition and control scenarios.