Finite-element modeling of low-stress suspension structures and applications in RF MEMS parallel-plate variable capacitors

This paper presents a complete structure and model of a microelectromechanical-system variable capacitor that is able to achieve a theoretically infinite tuning range. For the first time, both stress and residual stress issues are treated simultaneously. Two capacitors were fabricated where actuation voltages of 4.5 and 9 V (that correspond to a tuning range of 3:1 and 3.4:1, respectively) were acquired. Simulation and measurements verify that the proposed variable capacitors possess higher performance and tuning ranges when compared with the same class varactors fabricated using the same process. Further, a finite-element model based on electrostatic-structural coupling is presented.