An electrostatic MEMS spring actuator with large stroke and out-of-plane actuation

Abstract

A microelectromechanical system (MEMS) spring actuator based on the electrostatic repulsive force is presented. In general, an electrostatic-attractive-force-based actuator has a small stroke because instability results from the electrostatic pull-in effect. Therefore, a great deal of effort has been made to achieve large strokes for various applications. Based on the fact that an asymmetric electric field can produce an electrostatic repulsive force, an out-of-plane actuator has been demonstrated in this paper. The actuator consists of two layers which are parallel to each other. The top layer contains a central mass with a size of 100 µm × 100 µm × 2 µm, and it is suspended by a folding spring. The second layer is fixed to the substrate and works as the bottom electrodes of the actuator. The impacting factors to the repulsive force which consequently affect the displacement of the actuator are analyzed using finite element analysis software, and the optimal structure parameters have been obtained. The actuator is fabricated by the poly-multi-user-MEMS-process (PolyMUMPs); the measured out-of-plane displacement of this actuator reaches 2.7 µm at 50 V dc, and it shows good agreement with the simulation.