Authors: S. Pal, H. Xie
Affilation: University of Florida, United States
Pages: 685 - 688
Keywords: bimorph, curved bimorph, micromirror, thermal, piezoelectric, SMA, curved microactuator
Difference in strains in the two layers of a bimorph causes it to curl, thereby leading to actuation. Thermal, piezoelectric and shape-memory alloy based straight bimorph actuators have been widely reported. However, little attention has been paid to curved bimorphs which can greatly expand the design space for MEMS engineers. We propose a new class of microactuators based on curved bimorphs and report their analysis for the first time. The distinguishing feature of curved bimorphs is that bending and twisting deformations are coupled. The key equations in curved bimorph analysis are the force and moment balance equations, and strain continuity at the interface between the two layers. The strain consists of three components---thermal or piezoelectric strain, strain due to axial force, and bending strain. The bending moment due to strain and the equations governing the deflection of a curved beam are obtained from literature. Analytical expressions for the vertical deflection and bimorph twist are obtained. The analysis is validated via finite-element simulations. The center of a mirror-plate actuated by straight bimorphs shifts significantly during actuation. A novel design based on curved bimorph is proposed in which the mirror-plate center shift is only 0.4 microns for 13.5 degrees mirror tilt.