Impact dynamics of MEMS switches

During operation, a MEMS switch is activated by an applied voltage. This causes the switch, often a doped silicon microbeam, to be attracted toward (pulled-into) a substrate. The component–substrate contact completes a circuit and permits the flow of current. Calculations for the minimum voltage required to achieve quasi-static pull-in are well documented. But for these quasi-static pull-in voltages to be meaningful, the voltage would have to be increased gradually until the critical value V_pull-inV_{\mathrm{pull\mbox{-}in}} is reached and the switch closes. Of course, practical considerations might require the switch to cycle on and off quickly, i.e., dynamically. This is particularly true in the case of radio frequency (RF) MEMS switches. In this paper, a model is developed and used to consider the dynamic pull-in characteristics of a clamped-clamped microbeam. This model includes inertial effects, structural and air damping (squeeze-film damping), as well as the impact behavior of the microbeam with the substrate. Parameter combinations leading to various types of behavior (no pull-in, air-bounce, wall bounce, etc.) are clearly identified. In an attempt to ensure fast switch closure and limit bouncing, two new applied voltage profiles are considered.