▎ 摘　　要

We theoretically analyze the dynamics of a suspended graphene membrane which is in tunnel contact with grounded metallic electrodes and subjected to ac-electrostatic potential induced by a gate electrode. It is shown that for such a system the retardation effects in the electronic subsystem generate an effective pumping for the relatively slow mechanical vibrations if the driving frequency exceeds the inverse charge relaxation time. Under this condition there is a critical value of the driving voltage amplitude above which the pumping overcomes the intrinsic damping of the mechanical resonator, leading to a mechanical instability. This nonresonant instability is saturated by nonlinear damping and the system exhibits self-sustained oscillations of relatively large amplitude.