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Influences of W Content on the Phase Transformation Properties and the Associated Stress Change in Thin Film Substrate Combinations Studied by Fabrication and Characterization of Thin Film V1- xWxO2 Materials Libraries

Wang, X. and Rogalla, D. and Ludwig, Al.

ACS COMBINATORIAL SCIENCE
Volume: 20 Pages: 229-236
DOI: 10.1021/acscombsci.7b00192
Published: 2018

Abstract
The mechanical stress change of VO2 film substrate combinations during their reversible phase transformation makes them promising for applications in micro/nanoactuators. V1-xWxO2 thin film libraries were fabricated by reactive combinatorial cosputtering to investigate the effects of the addition of W on mechanical and other transformation properties. High-throughput characterization methods were used to systematically determine the composition spread, crystalline structure, surface topography, as well as the temperature-dependent phase transformation properties, that is, the hysteresis curves of the resistance and stress change. The study indicates that as x in V1-xWxO2 increases from 0.007 to 0.044 the crystalline structure gradually shifts from the VO2 (M) phase to the VO2 (R) phase. The transformation temperature decreases by 15 K/at. % and the resistance change is reduced to 1 order of magnitude, accompanied by a wider transition range and a narrower hysteresis with a minimal value of 1.8 K. A V1-xWxO2 library deposited on a Si3N4/SiO2-coated Si cantilever array wafer was used to study simultaneously the temperature-dependent stress change σ(T) of films with different W content through the phase transformation. Compared with σ(T) of ∼700 MPa of a VO2 film, σ(T) in V1-xWxO2 films decreases to ∼250 MPa. Meanwhile, σ(T) becomes less abrupt and occurs over a wider temperature range with decreased transformation temperatures. © 2018 American Chemical Society.

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