An innovative and simple method is proposed to achieve ultralinear behavior in a capacitance-versus-voltage response and to obtain a large capacitance tuning ratio in a parallel-plate microelectromechanical systems (MEMS) variable capacitor by moving the plate to an increasing-gap direction. By adopting a levering structure, the common closing-gap motion of the electrostatic actuator was transformed into an increasing-gap movement in order to decrease the capacitance as the actuation voltage was increased. By balancing out the rate that the plate moves up as the actuation voltage increased and the rate that the capacitance decreases as the plate moves up, high linearity was achieved. The proposed MEMS variable capacitor, which was fabricated via metal surface micromachining, showed an excellent linearity factor (LF) of 99.5% in the C-V response, and a capacitance tuning ratio of 134% was achieved in the actual usage range (10-45 V) at a low frequency. When it was operated at 1 GHz, the proposed device demonstrated an LF of 99.5% and a capacitance tuning ratio of 125%.
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