Effect of variation of design parameters on displacement and driving voltage of comb-drive actuators

A comb-drive actuator consists of two interdigitated comb structures, where one comb is fixed and the other comb is connected to a spring structure. A design of electrostatic comb-drive actuator is presented in this paper with different spring configurations i.e. fixed-fixed beam, crab-leg flexure beam and folded-flexure beam. The design parameters considered here are beam length, number of comb fingers and gap between the comb fingers. The effect of their variation on displacement and driving voltage of movable comb has been studied. Such actuators find extensive use in micro-positioning applications such as micro-tweezers. An increased displacement of comb drive actuator is subsequently accomplished for the same driving voltage, for folded-flexure beam configuration with increased beam length, higher number of comb-fingers and reduced gap between the comb-fingers. The beam length has been varied from 280μm to 320μm, number of moving comb fingers from 8 to 32 and gap between fingers has been reduced from 7μm to 1.6μm. The structures are further modified to decrease the requirement of driving voltage for even larger displacement, which include use of three-folded flexure and usage of jagged-shaped comb fingers and thus reducing requirement of driving voltage to 17V, increasing displacement to 11.102μm and increasing capacitance to 7819.728pF. Polysilicon is the structural material used for the designs. The simulation software used in this study is COMSOL Multiphysics, which offers Finite Element Analysis for calculation of displacement of movable fingers.