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 (T_tr) 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. T_tr 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 T_tr of the VO₂ layer underneath, either with or without a SiN diffusion barrier layer between the two. The shift of T_tr was by ~30 °C for a GST/VO₂ bilayered sample with thicknesses of 200/30 nm, and was by ~6 °C for a GST/SiN/VO₂ 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 VO₂ films could pave the way for the application of nonvolatile changes of optical properties in optoelectronic devices.