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 (ΣΔ) feedback loop as a control method of dielectric charging for capacitive microelectromechanical systems (MEMS). This technique allows setting of 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 ΣΔ 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.