This work presents the design, fabrication, and characterization of the first micro-electro-mechanical-systems (MEMS) mirrors where the actuation mechanism is based on the structural phase-change of smart material thin films monolithically integrated within the device. MEMS mirrors are microstructures with a reflective layer used to redirect incident light. They can be actuated by different techniques including electrostatic, electromagnetic, piezoelectric, and electrothermal mechanisms. In this work, the mechanical actuation of the device's platform (i.e. tilting angle and vertical displacement) is achieved by mechanical stress generated during the structural phase transition of a vanadium dioxide (VO2) thin film. VO2is a smart material with a solid-to-solid phase change transition at temperatures in the vicinity of 68° C, that shows hysteretic behavior spanning about 10° C. During the transition, the crystal structure of the VO2 changes from monoclinic to tetragonal. Consequently, the optical, electrical, and mechanical properties of the material change drastically. Since the transition temperature is very close to room temperature, VO2 can be integrated into MEMS devices lowering the power needed for maximum actuation. The device is operated electro-thermally through integrated resistive heaters, and its behavior is characterized across the phase transition of VO2. Individual actuation of each actuator allows for mirror tilting, while simultaneous actuation of the four legs allows for vertical displacement of the mirror platform. The integration of VO2 into the device allows for the programming of mechanical displacement for tilting angles and vertical displacements.
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