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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.

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This work presents micro-actuation of atomic force microscopy (AFM) cantilevers using piezoelectric Zinc Oxide (ZnO) thin film. In tapping mode AFM, the cantilever is driven near its resonant frequency by an external oscillator such as piezotube or stack of piezoelectric material. Use of integrated piezoelectric thin film for AFM cantilever eliminates the problems like inaccurate tuning and unwanted vibration modes. In this work, silicon AFM cantilevers were sputter deposited with ZnO piezoelectric film along with top and bottom metallic electrodes. The self-excitation of the ZnO coated AFM cantilever was studied using Laser Doppler Vibrometer (LDV). At its resonant frequency (227.11 kHz), the cantilever displacement varies linearly with applied excitation voltage. We observed an increase in the actuation response (131nm/V) due to improved quality of ZnO films deposited at 200 °C.

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