Charging in Dielectricless Capacitive RF-MEMS Switches

This paper presents results on high lifetime RF microelectromechanical (RF-MEMS) dielectricless capacitive switches. Using air gap variation only, these RF MEMS capacitive switches achieve a capacitance ratio of 9, associated with small residual charging. The reliability of the switch has been studied, pull-in and pull-out voltages shifts have been observed, modeled and validated with good agreement between model and measurements for a switch held for one month in the down state. The dependence of charging mechanism to the biasing signal is also presented by applying unipolar and bipolar waveforms with different duty cycles. Charging can be modeled using a simple Curie-Von Schweidler equation. It is shown that the duty cycle of the bias signal is strongly accelerating switch failure, and that using bipolar signals improves the lifetime of these switches by several orders of magnitude. The projected lifetime of current RF-MEMS dielectricless switches held in the down state using bipolar signals is several tens of years.