Design and Analysis of a Novel MEMS Variable Capacitor for RF Applications

A novel electrostatic RF MEMS variable capacitor consisting of a suspended top plate and two fixed bottom electrodes is presented. The fixed bottom electrodes are constructed by an inner fixed plate and an outer fixed plate. The inner fixed bottom plate is designed to provide electrostatic actuation for capacitance tuning and the outer one is coupled with the top plate to form a variable capacitor. The mechanical suspension of the top plate is served by four L-shaped cantilever beams, the spring constant of which has been analyzed. The characteristics of the proposed device have been analyzed through FEA software IntelliSuite and HFSS, and an extended tuning range of 78.9% is obtained. The achievable pull-in voltage is 20.2V. This capacitor operates over a wide frequency range from 1GHz to 20GHz with the return loss lower than 0.16 dB. Its quality factor is 119 at 5GHz when the applied voltage is zero.