On the effect of residual charges on the pull-in parameters of electrostatic actuators

In this paper a quantitative model for the effect of residual charges, located in dielectric coating layers, upon the pull-in parameters of electrostatic actuators is presented. Applying voltages higher than the pull-in voltage across the electrodes of an electrostatic actuator results in the collapse of the movable electrode of the actuator on the fixed one. In order to avoid short circuit, one or both of the electrodes can be coated by a dielectric isolating layer. Residual charges can accumulate in this dielectric coating and affect the behavior, and more specifically the pull-in parameters, of the electrostatic actuator. The model derived in this paper considers a general electrostatic actuator with a general charge distribution in the dielectric coating. The main interesting new results derived from the model are: (i) the pull-in displacement is unaffected by the residual charge and the travel range is only extended due to the series dielectric capacitor, (ii) the pull-in voltage is significantly reduced due to the residual charge, independent of the residual charge polarity and distribution.