MEMS variable capacitor with highly linear C-V response and large capacitance tuning ratio

Abstract

In this thesis, an innovative and simple method to achieve ultra-linear behavior in a capacitance vs. voltage response and a large capacitance tuning ratio in a parallel-plate MEMS variable capacitor by moving the plate to an increasing-gap direction is proposed. By adopting a levering structure, the common closing-gap motion of an electrostatic actuator was transformed to the increasing-gap movement so as to decrease the capacitance as we increase the actuation voltage. By balancing out the rate that the plate moves up as we increase the actuation voltage and the rate that the capacitance decreases as the plate moves up, we could achieve the high linearity. The proposed MEMS variable capacitor, which was made by metal surface micromachining, showed an excellent linearity factor of 99.5% in the C-V response and the capacitance tuning ratio of 134% was achieved in actual usage range (10 ~ 45V) at low frequency. When it was operated at 1GHz, the proposed device showed the linearity fac-tor of 99.5%, and the capacitance tuning ratio of 125%.