  Microphones exploit the motion of suspended membranes to detect sound waves.
Since the microphone performance can be improved by reducing the thickness and
mass of its sensing membrane, graphene-based microphones are expected to
outperform state-of-the-art microelectromechanical (MEMS) microphones and allow
further miniaturization of the device. Here, we present a laser vibrometry
study of the acoustic response of suspended multilayer graphene membranes for
microphone applications. We address performance parameters relevant for
acoustic sensing, including mechanical sensitivity, limit of detection and
nonlinear distortion, and discuss the trade-offs and limitations in the design
of graphene microphones. We demonstrate superior mechanical sensitivities of
the graphene membranes, reaching more than 2 orders of magnitude higher
compliances than commercial MEMS devices, and report a limit of detection as
low as 15 dBSPL, which is 10 - 15 dB lower than that featured by current MEMS
microphones.
