Pre-shaped buckled-beam actuators: Theory and experiments

Bistability is one of the desirable features for a MEMS actuator to have in various applications such as mechanical memories, micro-relays, micro-valves, optical switches, digital micro-mirrors, etc. It allows withdrawal of actuation force during idle periods without affecting an actuated state of a device, which results in minimal or even zero standing power consumption. One such actuator is a pre-shaped buckled beam. In this paper, theoretical analysis reveals that existence of the second stable state in a buckled-beam actuator depends not only on a ratio of its initial rise to its thickness, but also on its residual stress. Buckled-beam actuators are pre-shaped by layout design, fabricated by SU-8 lithography and copper pulse electroplating, and actuated by Lorentz force using an external magnet and current flow through the beams. Forward and backward critical loads or switching currents of the actuators are measured for various beam dimensions, and compared to the theoretical values. Required switching currents and voltages are between 10 and 200 mA, and between 20 mV and 0.4 V, respectively, for 20–60 μm displacement. Effect of electroplating conditions to bistability of actuators is studied as well.