Sigma Delta Effects and Charge Locking in Capacitive MEMS under Dielectric Charge Control

This work investigates, analytically and experimentally, the effects induced by the use of a first-order sigma-delta feedback loop as a control method of dielectric charging for capacitive MEMS. This technique allows one to set a desired level of net charge in the dielectric of a MEMS device by continuously alternating the polarity of the actuation voltage. This control system displays a number of interesting effects, inherited from sigma-delta modulation, and not usually found in conventional MEMS applications, with the charge locking phenomenon being the most relevant. The convergence time and the effectiveness of the control method are also investigated and discussed.