A graphene-based capacitive monolithic microphone with optimised air gap thickness and damping

A graphene-based capacitive monolithic microphone with optimized air gap thickness and damping has been designed, fabricated, and characterized. A bilayer poly(methylmethacrylate)/graphene membrane has been suspended as the movable plate. The membrane has been actuated electrostatically, electrothermally, and acoustically. The motion of the membrane on top of a 2-μm air gap and only one vent hole has been observed and studied, demonstrating the possibility to minimize both the air gap thickness and number of vent holes. During the fabrication process, an optimized combined wet and dry etching method to etch silicon dioxide has been applied to prevent the aluminum electrodes from being attacked. The effect of actuation voltage on displacement amplitude and resonant frequency has been studied. The microphone's mechanical and electrical sensitivity to sound has been characterized.