Analytical modeling for bulk-micromachined condenser microphones

Abstract

The advent of silicon micromachining technology has opened up numerous opportunities for the commercialization of many miniaturized sensors and one of the beneficiaries is the silicon condenser microphone. Simple analytical expressions, such as those formulated by Škvor/Starr for mechanical-thermal noise calculation, are used to describe the mechanical performance of a microelectromechanical system (MEMS) microphone. However, the location effect of acoustic holes is usually not considered on both frequency response and mechanical-thermal noise. In this paper, the theory of a condenser microphone is reviewed and a new analytical modeling method for the MEMS condenser microphones is proposed based on Zuckerwar’s model. With reference to a B&K MEMS microphone, the theoretical results obtained by the modeling method are in very good agreements with those experimental ones reported. It is also concluded that there is an optimum location for acoustic holes in the backplate. Finally, a new design for MEMS microphone with a polarization voltage of 10V is proposed, which has an open-circuit sensitivity of 2.1mV∕Pa (or −54dB ref. 1V∕Pa), a bandwidth of 18kHz, an A-weighted mechanical-thermal noise of 22dBA, and a signal-to-noise ratio of 60dB. This proposed microphone can be easily micromachined by using MEMS technology such as the deep reactive ion etching and wafer bonding technology.