Dimpled electrostatic MEMS actuators

We present electrostatic Micro-Electromechanical System actuators equipped with dimples and contact pads. The introduction of dimples and contact pads is shown to prevent stiction between the actuator and bottom electrodes and minimize dielectric charging and to eliminate multi-valuedness in the response. It also increases the stable travel range by eliminating the pull-in instability and introducing new “tapping mode” oscillations, where the dimples come into regular contact with the contact pads. An experimentally validated lumped-mass model was developed and used to generate the bifurcation diagram of the actuator in the vicinity of tapping mode oscillations. The diagram showed the presence of a chaotic attractor bracketed by a type-I intermittency and a cascade of period-doubling bifurcations. However, these chaotic motions were only present for a limited range of the excitation amplitude and frequency. Provided these ranges are excluded, dimples and contact pads can be deployed to obtain efficient and well regulated electrostatic actuators. We found that these results and conclusions are valid for classes of low-frequency as well as high-frequency actuators.