Design and Implementation of a Capacitive-Type Microphone With Rigid Diaphragm and Flexible Spring Using the Two Poly Silicon Micromachining Processes

This study reports the design and implementation of a novel capacitive-type micromachined microphone. The design of the microphone is based on the well-known two poly-Si layers micromachining processes. The microphone consists of a rigid diaphragm (the 2nd poly-Si layer), flexible springs (the 1st ply-Si layer), and rigid back plate (the 1st poly-Si layer). In short, the proposed microphone design has four merits, (1) the rigid diaphragm acting as the acoustic wave receiver and moving electrode is realized using the rib-reinforced poly-Si layer, (2) the flexible spring acting as the electrical routing as well as supporter for diaphragm is implemented using the thin poly-Si film, (3) the electrical routing of rigid diaphragm (moving electrode) is through the central poly-via and the flexible spring, and (4) the rigid plate acting as the stationary electrodes and back plate is fabricated using the high-aspect-ratio (HARM) trench-refilled poly-Si. To demonstrate the feasibility, the two poly-Si microphone has been implemented and tested. Typical measurement results show that the open-circuit sensitivity of the microphone was 12.63 mV/Pa (-37.97 dBV/Pa) at 1 kHz. (the reference sound-level is 94 dB).