Design of a high-Q CMOS-compatible MEMS tunable capacitor for RF applications

A high-Q micromachined electro-mechanically tunable capacitor for RF application is presented. The proposed design is CMOS-compatible that can be integrated monolithically with CMOS circuit in a single die. In this structure there is no need for cantilever beams which introduce considerable series resistance to the capacitor and decrease the quality factor. So our varactor achieve better Q in a smaller area. The simulated 1 pF capacitor shows a Q of 40 at 1 GHz and a tuning range of 42%. Pull-in voltage is 3.6 V which is a reasonable value for submicron CMOS technologies. To improve the Q, the top plate is modified to a double layer structure. In this case the top plate consists of 1 /spl mu/m thickness polysilicon and 0.5 /spl mu/m aluminum deposited on top of it. This design shows a Q of 47 at 1 GHz.