Design and FEM Modeling of an Electrostatic RFMEMS Varactor

This study presents a large tuning range RF MEMS variable capacitor using parallel plate structure. Electrostatic torsion actuator is used to change the capacitance. The actuator beams transform the closing gap of torsion actuator into the movement of capacitor plate in the upward direction. The varactor design is modeled using coupled field electrostatic-structural finite element method (FEM) simulations to achieve large tuning ratio. The proposed RF-MEMS varactor is modelled on 50 Ω coplanar transmission line for frequency range of 1-10 GHz, and resultant scattering parameters are achieved for both the actuated and un-actuated state. RF characteristics has been improved for actuated state. Best performance is achieved at 5.5GHz with large tuning ratio.