Stress-Induced In Situ Modification of Transition Temperature in VO2 Films Capped by Chalcogenide.

We attempted to modify the monoclinic–rutile structural phase transition temperature (Ttr) of a VO2 thin film in situ through stress caused by amorphous–crystalline phase change of a chalcogenide layer on it. VO2 films on C- or R-plane Al2O3 substrates were capped by Ge2Sb2Te5 (GST) films by means of rf magnetron sputtering. Ttr of the VO2 layer was evaluated through temperature-controlled measurements of optical reflection intensity and electrical resistance. Crystallization of the GST capping layer was accompanied by a significant drop in Ttr of the VO2 layer underneath, either with or without a SiNx diffusion barrier layer between the two. The shift of Ttr was by ~30 °C for a GST/VO2 bilayered sample with thicknesses of 200/30 nm, and was by ~6 °C for a GST/SiNx/VO2 trilayered sample of 200/10/6 nm. The lowering of Ttr was most probably caused by the volume reduction in GST during the amorphous–crystalline phase change. The stress-induced in in situ modification of Ttr in VO2 films could pave the way for the application of nonvolatile changes of optical properties in optoelectronic devices.