Analysis of the extended operation range of electrostatic actuators by current-pulse drive

A new driving mode of electrostatic actuators has been examined. It is based on charge drive rather than on voltage drive. Charge drive is accomplished by a pulsed current source delivering a given amount of charge to the actuator. It is theoretically shown that if the drive is ideal, any position across the gap is stable. The main reason underlying this result is that the electrostatic force does not depend on the remaining gap of the actuator and hence, the pull-in instability is avoided. These findings are supported on simulations using an analog high level description language allowing to represent the actuator by its differential equations. The effect of parasitic capacitances has also been examined and the stability conditions analyzed. A simple analytical stability condition can be written relating the value of the parasitic capacitance to the maximum deflection allowed for a stable equilibrium point. These results are also supported by simulation. Finally, the current leakage effects on the stability and drift of the equilibrium position have been analyzed. A trade-off between the relative loss of charge and the minimum refresh frequency required has been formulated.