Bandwidth and SNR enhancement of MEMS microphones using two poly-Si micromachining processes

This study employs the MOSBE process [1] to design and implement the MEMS microphone in Fig.1a to improve the signal-to-noise ratio (SNR) and the sensing range. The microphone has three merits: (1) rigid diaphragm without released holes together with ring-type oxide/polySi mesa could reduce the low frequency acoustic loss (Fig. lb); (2) rigid diaphragm supported by flexible V-shaped springs enables the parallel plate gap-closing capacitance sensing to improve sensing area and sensitivity (Fig.1b); (3) silicon nitride electrical isolation increases the sensing area to improve initial capacitance and noise floor (Fig.1c). Measurements indicate the fabricated microphone of 800μm diameter diaphragm: acoustic sensitivity is -39.8dB (Ref: 1V/1Pa) at 1kHz; +3dB bandwidth ranges 50-22kHz; and the SNR is over 54dB. Comparing with [2-3] in Table1, the presented microphone significantly improves the performances.