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

Joe Sakai,Yoichi Uehara,Kunio Okimura,Masashi Kuwahara

doi:10.3390/ma13235541

Abstract

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.

Highlights

In optoelectronic components such as switches, waveguides, transistors, and memories, the operation principle requires the control of electronic signals by light irradiation or the control of photonic signals by an electric field
It is striking that the stress-induced modulation of Ttr in VO2 was realized even when the VO2 layer was 10 times thicker (50 nm) than the GST layer (5 nm)
Combinations of a thin GST layer and a thick VO2 layer may be of use

Summary

Introduction

In optoelectronic components such as switches, waveguides, transistors, and memories, the operation principle requires the control of electronic signals by light irradiation or the control of photonic signals by an electric field. To realize such devices that are based on photon–electron interaction, materials that show phase transition accompanied by significant change in both electric properties (conductivity, etc.) and optical properties (reflectance, etc.) are strong candidates. The M–R phase transition of VO2 can be induced by heat, and by electric field [3,4], light [5,6], and mechanical strain [7], suggesting the possibility of realizing VO2 -based electrical/optical switching devices operated with these stimuli

Results

Discussion

Conclusion