MEMS microphone based on the membrane with bias voltage and FET (field effect transistor) mechano-electrical transduction

Abstract

Most commercially available microphones use a capacitive method, and their structure and performance are saturated to some extent. However, due to the limitation of the capacitive transduction method, the roll-off at the low frequency is inevitable, and there is a limit in reducing the mechanical thermal noise caused by the squeeze film damping that occurs between the membrane and backplate structure. Proposed FET (field effect transistor) based MEMS microphone detects a change in the source-drain current according to the gate voltage change of the FET induced by vibrating the membrane with the electric field. In the case of a MEMS microphone using the proposed FET, low frequency roll-off according to the energy conversion does not occur, and the size of the backplate can be drastically reduced as compared with the conventional MEMS microphone, thereby further reducing the mechanical thermal noise, leading to the possibility of achieving the higher SNR (signal to noise ratio). In this study, design and fabrication, performance test of the proposed FET based MEMS microphone are conducted. [Work supported by CMTC, UM15304RD3.]

A Review of MEMS Capacitive Microphones

“…However, their works were not followed through due to the high noise floor. Recently, we have seen publications that attempted to solve this problem [114,135,136], with some groups promoting CMOS-MEMS process [134,136] as the best solution to accomplish this goal. If these solutions are practical and proven to reduce the level of noise floor, this direction of research will be a gold mine for industry, as it pushes the cost and footprint lower.…”