Abstract
This study designs and implements the differential MEMS microphone (Fig. 1) to improve its signal-to-noise ratio (SNR) and sensing range using MOSBE process [1]. The microphone has three major merits: (1) achieve Differential MEMS Microphone using top/bottom diaphragm and top/bottom back-plate formed by two poly-Si layers (Fig. 1b); (2) reduce Low Frequency Acoustic Loss by removing release holes and adding surrounding mesa for diaphragm (Fig. 1b); (3) improve Sensing Area and Sensitivity through parallel plate gap-closing capacitance sensing enabled by rigid diaphragm with flexible U-shaped springs (Fig. 1c); and one minor merits: single sacrificial layer to define differential sensing gaps to reduce process induced thickness variation. Measurements indicate microphone of 800 mumathrm{m} 'diameter' diaphragm: acoustic differential sensitivity is -40.5dB (Ref: 1V/1Pa) at 1kHz; ±3dB bandwidth ranges 50-20kHz; and the SNR is over 57.8dB.