Voltage-Controlled $C{-}V$ Response Tuning in a Parallel Plate MEMS Variable Capacitor

In a conventional parallel plate MEMS variable capacitor, the capacitance versus voltage response (C-V response) has been deterministic. In this work, the C-V response is tuned versatilely through the application of a control voltage to an additional electrode in order that the initial gap between the parallel capacitor plates is set by the control voltage. Then, the capacitor plates are lifted (capacitance decreases) as the actuation voltage applied to the levering actuator increases. In this manner, the shape of the C-V response can be controlled even after the device is fabricated. At a zero control voltage, the fabricated MEMS variable capacitor exhibited a convex shape in the C-V response (i.e., the capacitance decreases slowly in the low actuation voltage region and rapidly in the high actuation voltage region). When 3 V was applied to the control voltage, the capacitor exhibited an almost linear C-V response with a linearity factor of 0.999. At 5 V of control voltage, the C-V response changed to a relatively concave shape (i.e., the capacitance decreases rapidly in the low actuation voltage region and slowly in the high actuation voltage region). The capacitance tuning ratio of the fabricated device exceeded 120% at all control voltages. The proposed C-V response tuning capability is vital and amenable to various circuit demands.