Shape and Thermal Effects of Metal Films on Stress-Induced Bending of Micromachined Bilayer Cantilever

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In this study, the shape and thermal effects of metal films on the stress-induced bending of micromachined bilayer cantilever are systematically investigated. The cantilever makes use of residual stresses in thin films to induce the bending of microstructures by applying preloads. The characterization of the bilayer cantilever with different Au distribution has been performed to observe out-of-plane deformation. A finite-element model has been established to analyze such a deformation using experimental and theoretical results. It indicates that the commonly used formula for predicting the deformation of the cantilever is not valid for these devices. When the percentage of the area deposited with a metal is increased, deflection angle also increases. Furthermore, the influence of postprocessing temperature on the residual stress of the metal films is examined. Postprocessing temperature and residual stress reveal a close relationship. As postprocessing temperature increases, the residual stress of the metal increases, resulting in a larger out-of-plane deformation of the cantilever. Residual stress increases to a saturation value while the temperature reaches a critical value. This new finding could greatly affect the performance of a stress-induced bilayer cantilever. Finally, a switchable micromachined corner mirror is demonstrated using the bilayer cantilever.
2005-05-15