A high-fidelity MEMS microphone with a polymer membrane that can detect infra-sounds

This study proposes a polymer MEMS microphone that operates through electromechanical amplitude modulation. We have developed a highly optimized MEMS structure with a flexible polymer material, resulting in a miniaturized and flexible device with excellent acoustic performance. The stiffness and damping characteristics of the polymer diaphragm are analyzed and it shows that the polymer material would be suitable for microphone applications. An equivalent circuit model is also developed for design purposes, so that the device could be properly designed using it and fabricated by in-house polymer thin film processes. The fabricated device is tested using a DC bias scheme to reach its signal-to-noise ratio (SNR) of 65 dBA within a bandwidth of 10 to 10,000 Hz, which is comparable to existing high-end commercial silicon MEMS microphones. We would then extend the frequency bands of linear detection down to the infrasound range by using electromechanical amplitude modulation. This operation scheme can also provide the microphone with no need for metal packaging. Its feasibility is confirmed theoretically by numerical simulations including electromechanical amplitude modulation and experimentally by implementing it at the PCB level. In addition, this approach enables the sensor stronger to the environmental noise so that metal shielding could be omitted.