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

Xiao Wang, Detlef Rogalla, Alfred Ludwig

Index: 10.1021/acscombsci.7b00192

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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.