A novel high tuning ratio MEMS cantilever variable capacitor

Abstract

This paper presents a novel cantilever-type MEMS variable capacitor with high tuning ratio. In previous works, the cantilever is used as a switch but in our design, it is applied as a variable capacitor. For increasing the maximum achievable capacitance of the cantilever, the suspended capacitive plate should be moved as parallel with fixed plate. The parallel movement can be obtained using the novel structure which utilized two additional lateral beams. Also to overcome the pull-in phenomenon in new structure, the different membrane thickness technique is used. The novelty of our design is adding the lateral beams to make parallel movement of the suspended plate to increase the variable capacitor of the cantilever. The new device is designed on a thick silicon substrate with a thin poly silicon membrane. The results show the tuning range of tunable capacitor with initial capacitance of 560.1 fF can be improved from 6:1 for conventional cantilever to 22.5:1 for the new cantilever. In other words the capacitance tuning range increased three times.