Effect of Nonlinear Structural Stiffness on the Response of Capacitive MEMS Devices

The effect of flexibility and initial curvature of moving plates in parallel-plate MEMS capacitors are investigated. A parallel-plate-based MEMS tunable capacitor with extended tunability and linear capacitance-voltage (C-V) response is introduced. The design combines the flexibility and curvature of the electrode with an array of mechanical stoppers to increase the overall stiffness of the device as the actuation voltage increases. The plate’s curvature and the location of the stoppers are tailored to provide a smooth CV curve with high linearity and fairly constant sensitivity throughout the working range. ANSYS FEM simulations and experimental results of capacitors fabricated with PolyMUMPs demonstrate a notable improvement in the linearity of the C-V response comparing to that of a conventional parallel-plate capacitor. The proposed technique can also be applied to capacitive pressure and temperature sensors and electrostatic actuators to enhance their performances.