Parametric Optimization of RF MEMS Variable Capacitor with High Linearity for C-Band Applications

A novel RF Microelectromechanical System (MEMS) Variable capacitor is proposed to obtain a linear capacitance-voltage response and large tuning ratio. Rectangular electrostatic torsion actuators are connected to each end of the central capacitor plate by using actuator beams. When voltage is provided in the actuator section, the actuator beam assists in providing steady movement of the central plate in an upward direction. Structural optimization of the RF MEMS Varactor is performed from the perspective of capacitance-voltage response by using ANSYS. The research provides a notable dual contribution that includes both substantial tunability and high linearity. It demonstrates a high capacitance tuning ratio of 312% and a 99% linearity factor in the C-V response, indicating a high linearity factor. The optimized design is demonstrated on a 50-ohm coplanar transmission line to obtain S-parameters by using HFSS. Characteristics of RF performance are analyzed by comparing SiO2 with Si3N4 as the dielectric material in this design. At 4.2 GHz, the varactor with Si3N4 shows -50.2 dB isolation, while the varactor with SiO2 shows -48.2 dB isolation at 5.5 GHz. The proposed study shows that the optimized RF MEMS Varactor shows better performance using Si3N4 at lower frequencies, which makes it appropriate for C-Band applications.