A Robust RF MEMS Variable Capacitor with Piezoelectric and Electrostatic Actuation

An RF MEMS variable capacitor using hybrid actuation of piezoelectric and electrostatic forces is presented. A surface micromachining process is used to fabricate the device. The piezoelectric actuator, which uses thin film PZT, enables low voltage actuation while the electrostatic actuator realizes large capacitance ratio. The measured capacitance ratio is Cmax/Cmin=14 at 5V. We demonstrate that the hybrid actuation enables to lower the pull-in voltage without changing the pull-out voltage. We also show that the shift of pull-out voltage due to dielectric charging can be reduced drastically at actuation voltages below 10V. In this sense, the hybrid actuation can realize low voltage operation with enhanced robustness for stiction