Feasibility study of a MEMS microphone design using the PolyMUMPs process

The scope of this paper is to underline the design issues of MEMS microphones and presents a test case designed using the PolyMUMPs process with an additional back-etch processing step. Both circular and square (simply supported and clamped) diaphragm designs are considered. The effect of the back chamber volume on the microphone sensitivity is also investigated. The finalized design is based on the clamped square diaphragm with a bottom sound port. The bias voltage is 6 V and the diaphragm has a side-length of 675 μm. The back-plate includes several holes which amount to a perforation ratio of 0.33. The maximum allowable input pressure before pull-in is 139 dB SPL. The microphone with a back-chamber volume of 6 mm3 has a sensitivity of 8.4 mV/Pa at 94 dB SPL at 1 kHz. The complete package size with the ASIC included is targeted to be 3×2.5×1 mm, assuming that the ASIC is of a comparable size to that of the MEMS sensor.