Cantilever beam electrostatic MEMS actuators beyond pull-in
The operational range of electrostatic MEMS parallel plate actuators can be extended beyond pull-in in 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 along with a dielectric layer. The results from the simple beam model are validated with 3D simulations performed in CoventorWare™. 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 bi-stable and tri-stable states exist. A classification of all possible transitions (pull-in and pull-out as well as transitions we term pull-down and pull-up) is presented based on the dielectric layer parameters. Dynamic stability analyses are 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 overall tunability.