Breaking the size barrier of capacitive MEMS microphones from critical length scale

Based on the synergy of a theoretical one-dimensional (1D) mass-spring-damper model and the experimental validation of fabricated capacitive MEMS microphones fabricated by the PolyMUMPs process, we identify the existence of a critical diaphragm radius which represents the inflection point on the microphone's sensitivity-radius curve. To overcome this miniaturization barrier, we propose a new microphone structure with four folded microbeams. The corresponding sensitivity remains the same, while the radius reduces by 17% in comparison with the previous design.