Large-stroke microelectrostatic actuators for vertical translation of micromirrors used in adaptive optics

Two microelectrostatic actuators able to produce a repulsive force in the out-of-plane direction are presented in this paper. The electrostatic actuators use an asymmetric electric field surrounding the top and bottom surfaces of the moving fingers to produce a repulsive force. The displacement of translation micromirrors driven by these actuators is not limited by the "pull-in" effect and, therefore, can achieve a large stroke. In addition, the usage of a repulsive force leads to the elimination of the stiction problem. An analytical model relating the displacement of the first actuator to voltage applied is presented. The analytical model and numerical simulations show that a translation micromirror driven by the first actuator can achieve a stroke as large as 6/spl mu/m at a driving voltage of 50 V. The second actuator, suitable for fabrication using Multi-User-MEMS-Processes (MUMPs), is developed. A prototype translation micromirror driven by the second actuator achieved a vertical stroke of 2 /spl mu/m, which is more than three times the stroke of conventional MUMPs translation micromirrors.