  To realize nanomechanical graphene-based pressure and gas sensors, it is
beneficial to have a method to electrically readout the static displacement of
a suspended graphene membrane. Capacitive readout, typical in
micro-electro-mechanical systems (MEMS), gets increasingly challenging as one
starts shrinking the dimensions of these devices, since the expected
responsivity of such devices is below 0.1 aF/Pa. To overcome the challenges of
detecting small capacitance changes, we design an electrical readout device
fabricated on top of an insulating quartz substrate, maximizing the
contribution of the suspended membrane to the total capacitance of the device.
The capacitance of the drum is further increased by reducing the gap size to
110 nm. Using external pressure load, we demonstrate successful detection of
capacitance changes of a single graphene drum down to 50 aF, and pressure
differences down to 25 mbar.
