Electrostatic shunt RF MEMS switch with a floating electrode for S-band applications: architecture and mathematical modeling

This paper presents the design and modeling of an electrostatically actuated capacitive shunt RF MEMS switch with a floating electrode for S-band operation. The proposed architecture incorporates a mechanically fixed, electrically floating metal electrode positioned above the signal line and separated from it by a high-k TiO₂ dielectric layer. This configuration substantially increases the down-state capacitance and improves signal isolation without requiring extremely small interelectrode gaps. The switch is implemented on a coplanar waveguide and uses an aluminum membrane with meander suspensions and perforation to reduce the effective stiffness, actuation voltage, and switching time. The main electromechanical parameters were evaluated analytically and verified by finite element modeling in COMSOL Multiphysics, while the RF performance was analyzed using electromagnetic simulation in ANSYS HFSS. The final design demonstrates a pull-in voltage of 2.7 V, a closing time of 18 μs, a down-state capacitance of 247 pF, and an up-state capacitance of 9.6 fF. In the 2−4 GHz range, the simulated up-state insertion loss is from -0.012 to -0.14 dB, and the down-state isolation is from -43.3 to -89.75 dB. The results show that the floating-electrode architecture provides a high capacitance ratio and significantly enhances the RF performance of the capacitive shunt MEMS switch.