MEMS-based piezoresistive and capacitive microphones: A review on materials and methods

Microelectromechanical systems (MEMS)-based piezoresistive and capacitive microphones have gained sig-nificant attention due to their miniaturization, high performance, and diverse applications. This review paper provides a comprehensive overview of the materials and methods employed in these microphone technologies. We discussed various transduction mechanisms, including electrostatic, piezoresistive, and piezoelectric, along with their working principles and advantages. Additionally, we explored the utilization of surface acoustic wave (SAW) and bulk acoustic wave (BAW) resonators in microphone design. Performance characteristics such as sensitivity, noise floor, linearity, dynamic range, and bandwidth are analyzed, highlighting the key factors influencing microphone performance. Furthermore, we delve into the application areas of these microphones, ranging from aircraft design and satellite launching to biomedical fields and audio engineering. Lastly, we discuss the materials used for MEMS microphones, focusing on substrate materials, etchant materials, and the specific requirements for piezoresistive and capacitive materials based microphones. Further, this review paper explores the emerging trends of graphene-based microphones, MEMS/NEMS hybrid devices, and the integration of artificial intelligence and signal processing techniques, as well as the potential applications in biomedical and healthcare fields, providing a comprehensive overview of the materials and methods employed in MEMS-based capacitive and piezoresistive microphones.