Design and characterization of a MEMS piezoelectric acoustic sensor with the enhanced signal-to-noise ratio

Abstract

The signal-to-noise ratio (SNR) – governed by the sensitivity and noise – determines the usefulness of a MEMS acoustic sensor. Low-SNR poses functional inability in a noisy environment and difficulty in signal processing. The literature is abundant with various approaches to mitigate low-SNR, however, it shows a lack of simultaneous improvement of sensitivity and noise. This paper reports on a MEMS piezoelectric acoustic sensor (PAS) with 7–30 dB higher SNR as compared to the state-of-the-art of PAS. The developed PAS uses analytically modeled aluminum nitride (AlN), and D33 transducer mode with a nominal electrode spacing, i.e., 20 μm. At 1 kHz frequency, the measured SNR is found to be 67.03 dB which varies from 70 dB to 85 dB in the bandwidth. In addition to the substantial improvement of the SNR, the equivalent input-referred noise (EIN) is found to be 26.97 dB SPL; whereas, the A-weighted noise is 27.23 dBA which is the lowest noise ever analytically and experimentally reported in the state-of-the-art of PAS. Notably, all the measured results are found in full compliance with the analytical predictions. With the analytical and experimental results – in addition to its millimeter size – the developed PAS can be implemented in some cutting edge applications where an acoustic sensor with very high SNR is required like a mobile robot, noise monitoring, position tracking of the incoming sound, and voice-activated human-computer interaction.