Analysis and design of an electrostatic MEMS microphone using the PolyMUMPs process

Abstract

This paper presents the analysis and design of an electrostatic MEMS microphone using the PolyMUMPs process with an additional back-etch processing step. Circular and square (simply supported and clamped) diaphragm designs are considered and analyzed, with the final design being based on the clamped square diaphragm with a bottom sound port. Although simply supported diaphragms exhibit high sensitivity for a given size, most MEMS fabrication processes such as the PolyMUMPS process, can only support clamped diaphragms. The effect of the back chamber volume on the microphone sensitivity is also investigated. 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 exhibits a sensitivity of 8.4 mV/Pa at 94 dB SPL at an operating frequency of 1 kHz.