Single Electrode Bidirectional Switching of Latchable Prestressed Bistable Micromechanical Beams

Abstract

Electrostatically actuated, bistable, curved micromechanical beams can exhibit latching, wherein the beams remain in two distinct stable states without an applied voltage. These structures could serve as building blocks in a variety of applications such as micromechanical logic elements, switches, non-volatile memories, and low power consumption sensors. However, the design of such devices is challenging since such structures are prone to symmetry breaking, which consequently inhibits latching. Generally, asymmetric responses may be circumvented by introducing a tailored axial compressive prestress. In this work we explore, both theoretically and experimentally, the influence of prestress on the single electrode, bidirectional dynamic switching of curved, latchable, single crystal Si <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 1000 \;\mu \text{m}$ </tex-math></inline-formula> long and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 3.5\;\mu \text{m}$ </tex-math></inline-formula> wide beams. We use Joule heating to apply the necessary prestress required to eliminate symmetry breaking and ensure latching. In accordance with reduced-order model predictions, our experimental findings show that prestress plays a key role in the dynamic response of the beam. Our results demonstrate bidirectional operation using a single electrode, fostering a compact footprint device for tailoring the axial stress and dynamic conditions.