Design considerations of a large-displacement multistable micro actuator with serially connected bistable elements

Abstract

In this work we report on a finite element modeling and design methodology, fabrication and characterization of a large-displacement low voltage multistable micro actuator with an integrated electrostatic comb drive transducer. The compliant suspension of the device incorporates multiple serially connected bistable arch-shaped beams and exhibits controllable sequential snap-through buckling under an increasing actuation force. The device can be considered therefore as an example of a compliant multistep structure. The device is also distinguished by its ability to remain in several different stable configurations at the same actuation voltage while the force–displacement characteristic of the suspension can be tailored by changing the geometry parameters of the flexures. A model built using the shallow arch approximation along with a nonlinear finite element analysis were used in order to study the influence of the suspension architecture on the stability limits of the structure and for evaluation of design parameters of the actuator. Bistable and multistable devices were fabricated by a Deep Reactive Ion Etching (DRIE) based process using silicon-on-insulator (SOI) wafers. Experimental results, which are consistent with the model predictions, demonstrate that the compliant multistep devices exhibit improved lateral stability and consequently larger stable displacements compared to the conventional comb drive actuators. Stable displacements up to 80 μm at a voltage of 30 V were registered in the experiments while three snap-through and snap-back events took place during loading and unloading, respectively. Our computational and experimental results show that the suggested device has clear functional advantages and can be efficiently used in applications including switches, threshold inertial sensors, variable optical attenuators as well as in micro-and nanomechanical logical elements.