A MEMS microphone with repulsive sensing

Abstract

The most common types of MEMS microphones are based on the capacitive sensing principle because of their ease of integration and their ability to detect low pressure fluctuations. One bottleneck in the design of conventional electrostatic MEMS microphones is that the sensitivity is impaired by the pull-in effect in parallel-plate capacitors. The electrical sensitivity of the microphone is a linear function of the bias voltage applied on the microphone. To increase the sensitivity and signal to noise ratio, the bias voltage should be increased, but the bias voltage is severely limited to the pull-in voltage, where the diaphragm will collapse into the backplate. To address the sensitivity issue in MEMS microphones, we devised a new type of capacitive sensor that creates a repulsive force rather than an attractive force, thereby completely avoiding the pull-in effect. The pull-in voltage has constrained the performance of capacitive microphones since their invention by Edward C. Wente in 1916. The ability to...