Fabrication and Experimental Characterization of a MEMS Microphone Using Electrostatic Levitation

Fabrication and acoustic performance of a micro-electromechanical systems (MEMS) microphone are presented. The microphone uses an unusual electrostatic sensing scheme that causes the sensing electrode to move away, or levitate, from the biasing electrode as the bias voltage is applied. This approach differs from existing electrostatic sensors and completely avoids the usual collapse known as pull-in instability. In this study, our goal is to fabricate a MEMS microphone whose sensitivity could be improved simply by increasing the bias voltage, without suffering from pull-in. The microphone is successfully fabricated and tested in our anechoic chamber. A read-out circuit is used to obtain electrical signals in response to sound pressure at various bias voltages. Experimental results show that the sensitivity increases approximately linearly with bias voltage for bias voltages from 40 volts to 100 volts. The ability to design electrostatic sensors without concerns about pull-in failure permits a wide range of promising sensor designs.