Analysis of Pull-in Behavior of Electrostatic MEMS Actuators for Optical Switching Applications

Micro Electromechanical Systems (MEMS) actuators experience pull-in instability in their actuation range. MEMS actuating elements are thin parallel plate capacitor electrodes separated with air gap. The electrodes are fabricated from silicon as substrate layer and gold /aluminum layer as functional layer for reflecting laser beam in optical switching application. When the top electrode is attracted towards bottom electrode, as it crosses one third distance of the gap between the electrodes, it undergoes pull-in/snap-down with bottom electrode. This condition severely limits the device operating range. These devices are operated either analog or digital mode for positioning of the top electrode. The plate electrodes actuated in tilting mode or bending mode and they are typically torsional structures or fixed-fixed structures. This paper provides theoretical pull-in analysis for the static behavior of a optical switch model. It is derived from analytical modeling of the parallel plate type with fixed-fixed structural end conditions. The effect of dielectric layer thickness is taken into account for predicting the pull-in voltage. During the piston mode actuation cycle, when the threshold (pull-in) voltage is reached, the switch is in the bent or ON state due to electrostatic repulsion/attraction and for the no voltage condition it is in the parallel or OFF state. The pull-in hysteresis behavior of the multilayered micro-actuator bending beam model is analyzed for the variation in thickness of dielectric material. In this paper, the critical role of different dielectric layer materials in bringing down the static pull-in voltage is discussed.