Spontaneous oscillation due to charging effect in MEMS RF switches

A spontaneous oscillation due to charging effect in an RF MEMS switch was investigated. When an RF MEMS switch opens from its contact mode, a nano-scale gap is formed and the charges accumulate between the movable and fixed electrodes, which cause a strong attractive force in the gap. The attractive force draws the electrodes to contact each other again, thus the charges are neutralized. As the charges are cyclically accumulated and dissipated, the intermittent excessive electrostatic force is generated, leading to the repeated pull-in/contact/pull-out motions at tens of kHz. The lifetime of MEMS switches was reduced because the electrode surfaces were degraded after cyclical excessive contacts by the oscillations. The spontaneous oscillation was analyzed theoretically by the extended Qucs model. The experiments were performed to validate the investigated effect of the spontaneous oscillation.