Feasibility study of a MEMS microphone based on the piezoresistivity of a field-effect transistor

This study demonstrates the feasibility of a MEMS microphone employing the piezoresistive effect of a field-effect transistor (PrFET microphone). Previous piezoresistive microphones feature a simple sensing structure consisting of a single diaphragm and are compatible with CMOS processes. Moreover, the low-frequency roll-off inherent to capacitive and piezoelectric microphones is fundamentally absent. However, their reliance on high-resistance sensing elements results in the degradation of both sensitivity and noise characteristics. The proposed PrFET microphone utilizes the FET channel as the piezoresistive sensing element. It is fabricated in a single-diaphragm structure using CMOS-compatible processes and detects acoustic signals through a transconductance amplifier. Due to the absence of a high resistance of sensing element, it achieves higher sensitivity than the existing piezoresistive microphone. The PrFET microphone is expected to achieve improved performance through various designs of sensing structures or signal processing techniques, facilitating the development of various types of miniaturized acoustic sensors.