Phase transition induced micromechanical actuation in VO₂ coated cantilever

Structural phase transition assisted micromechanical actuation of a vanadium dioxide (VO₂) coated silicon microcantilever is presented. A 300 nm polycrystalline VO₂ film was deposited over the silicon surface at 520 °C using metal organic chemical vapor deposition. The formation of the M1 monoclinic phase of the as-deposited VO₂ film was confirmed by X-ray diffraction studies and further verified by temperature variable Raman spectroscopy. The heated VO₂ film exhibits semiconductor-to-metal transition at 74 °C, which produces a change in the electrical resistance almost of three orders in magnitude. Consequently, the VO₂ film undergoes structural phase transition from the monoclinic phase (011)_M1 to a tetragonal phase (110)_R. This generates a compressive stress within the VO₂ film resulting in large, reversible cantilever deflection. This deflection was measured with a non-contact 3D optical profilometer, which does not require any vacuum conditions. Upon heating, the VO₂ coated silicon cantilever produced a large reversible tip deflection of 14 μm at 50 °C. Several heating and cooling cycles indicate steep changes in the cantilever tip deflection with negligible hysteresis. In addition, the effect of thermal stress induced cantilever deflection was estimated to be as small as 6.4%, and hence can be ignored. These results were found to be repeatable within controlled experimental conditions.