Design and Characterization of a Micro-Fabricated Graphene-Based MEMS Microphone

We fabricate a MEMS microphone that incorporates a graphene-based membrane that vibrates in response to acoustic forcing. We employ a novel fabrication process, where a graphene/PMMA bilayer membrane is transferred over a cavity on a separate chip before being affixed to the surface of another chip containing an electrode, resulting in the fabrication of a moveable capacitor with a membrane-to-electrode gap of 8 µm. The gap, which is less than half the size of other reported graphene membrane-based audio transducers, allows for the device to operate with low DC bias voltages of about 1 V and, when integrated with a custom-designed readout circuit, demonstrates a sensitivity to sound pressure between 0.1 mV/Pa and 10 mV/Pa across the range 100 Hz to 20 kHz. As well as a sensitivity that is comparable to previous work, the flat frequency response is stable when the sound pressure is varied between 70dB_SPL and 80dB_SPL, with the sensitivity value not varying by more than 0.2 mV/Pa.