Design and optimization of a new highly linear tunable mems capacitor

In this paper, a novel linearly tunable MEMS capacitor with high tunability is introduced. The characteristic air gap-voltage curve for an ideally linear tunable capacitor is studied. This curve is considered as a target for new designs. A three-structural layer process is used to develop the capacitor. The actuation and sense gaps in the three-plate capacitor are selected in such a way that for a voltage interval (between zero and pull-in), the gap-voltage response for sense electrodes becomes similar to the ideal curve. The resulting capacitance-voltage response of the new design demonstrates a combination of high linearity and tunability up to 250%. For processes which have fixed layer thickness and the sense and actuation gaps cannot be optimized, the design is modified by adding nonlinear springs and asymmetric geometry. The results of numerical simulation for a capacitor designed for PolyMUMPs process verify the improvement of linearity and tunability.