Mems Parallel Plate Actuators: Pull-in, Pull-out and Other Transitions

The operational range of MEMS electrostatic parallel plate actuators can be extended beyond pull-in with the presence of an intermediate dielectric layer, which has a significant effect on the behavior of such actuators. Here we study the behavior of cantilever beam electrostatic actuators beyond pull-in, using a beam model. Three possible static configurations of the beam are identified over the operational voltage range. We call them floating, pinned and flat: the latter two are also called arc-type and S-type in the literature. We compute the voltage ranges over which the three configurations can exist, and the points where transitions occur between these configurations. Voltage ranges are identified where where bi-stable and tri-stable states can exist. A classification of all possible transitions, based on the dielectric layer parameters, is presented. Dynamic stability analysis is presented for the floating and pinned configurations. For high dielectric layer thickness, discontinuous transitions between configurations disappear and the actuator has smooth predictable behavior, but at the expense of lower tunability. We suggest that variable dielectric layer thickness may be used to obtain both regularity/predictability as well as high tunability.