Stress-Induced In Situ Modification of Transition Temperature in VO(2) Films Capped by Chalcogenide

We attempted to modify the monoclinic–rutile structural phase transition temperature (T(tr)) of a VO(2) thin film in situ through stress caused by amorphous–crystalline phase change of a chalcogenide layer on it. VO(2) films on C- or R-plane Al(2)O(3) substrates were capped by Ge(2)Sb(2)Te(5) (GST) films by means of rf magnetron sputtering. T(tr) of the VO(2) 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 T(tr) of the VO(2) layer underneath, either with or without a SiN(x) diffusion barrier layer between the two. The shift of T(tr) was by ~30 °C for a GST/VO(2) bilayered sample with thicknesses of 200/30 nm, and was by ~6 °C for a GST/SiN(x)/VO(2) trilayered sample of 200/10/6 nm. The lowering of T(tr) was most probably caused by the volume reduction in GST during the amorphous–crystalline phase change. The stress-induced in in situ modification of T(tr) in VO(2) films could pave the way for the application of nonvolatile changes of optical properties in optoelectronic devices.