Development of a no-back-plate SOI MEMS condenser microphone

This study demonstrates a SOI condenser MEMS microphone consisting of planar interdigitated sensing electrodes, deformable diaphragm, and back chamber. No back-plate is required for this design, thus, the acoustic impedance is reduced. The merits of this study are: (1) the back-plate is replaced by planar interdigitated sensing electrodes to prevent in-use pull-in and process stiction between diaphragm and back-plate, (2) out-of-plane area-changing capacitive sensing provides a better linearity to sound pressure variation, (3) large and flat diaphragm implemented by SOI and DRIE process increases the acoustic sensitivity. The proposed microphone with 600μm diameter diaphragm and 42 pairs sensing electrodes is realized and tested. Measurements show a flat response between 1 kHz to 20 kHz. The sensitivity of microphone is -60.1dB (ref. 1V/1Pa) at 1 kHz.