A capacitive-piezoelectric hybrid MEMS microphone with signal fusion for enhancing signal-to-noise ratio

This work describes a hybrid micro-electro-mechanical-systems (MEMS) microphone integrating capacitive and piezoelectric transduction mechanisms for signal-to-noise ratio (SNR) improvement. A theoretical system-level model was established to characterize the hybrid device, which was fabricated using a silicon-on-insulator (SOI) wafer-based process. The piezoelectric transduction component employs a Si/SiO2/Au/AlN/Pt material stack, while the capacitive transduction part consists of a variable capacitor formed by a silicon handle layer and a silicon device layer. Experimental results at 1 kHz show that the hybrid MEMS microphone achieves sensitivities of -64.3 dB (re: 1 V/Pa) in piezoelectric mode, -54.9 dB (re: 1 V/Pa) in capacitive mode, and -52.4 dB (re: 1 V/Pa) in hybrid mode, with corresponding SNR values of 65.7 dB, 59.8 dB, and 62.2 dB, respectively. To enhance the overall SNR of the hybrid MEMS microphone, a signal fusion technique is applied to the dual synchronized signals, resulting in an enhanced SNR of 66.7 dB, exhibiting a 14.1 dB improvement compared to the 52.6 dB reported in previous work.