Design and analysis a novel RF MEMS switched capacitor for low pull-in voltage application

Abstract

In this paper, we design and analysis a new RF MEMS switched capacitor that exhibits low pull in voltage. We propose a capacitance calculation method based on conformal mapping for the coupled open-ends in coplanar waveguide (CPW), an inductance computational method based on twin strip structure for the coupled short-ends in CPW, and an analytical pull-in model of the switched capacitor. A process optimization way for planarization of polyimide surface is proposed, resulting in polyimide surface roughness less than 10 nm. A new low pull-in voltage RF MEMS switched capacitor is fabricated and the lumped RLC model circuit is extracted. Measured results demonstrate an entirely pull in voltage of only 16 V for the switched capacitor, meanwhile the capacitance ratio is 6.8. Under hot-switched and 100 mW conditions, the pull in voltage is still 16 V. A hot-switched of an actuation voltage reduces to 13 V with a power of ~300 mW, furthermore, the capacitance ratio changes to 5. The device is tested under hold-down conditions of over 90 s, the actuation voltage drops to 11.6 V, and the capacitance ratio never changes.