Strain-Free Vanadium Dioxide Films with Stable Phase-Transition Temperatures for Flexible Phase Change Devices

Strain has significant influence on the semiconductor–metal transition (SMT) of vanadium dioxide (VO2) and has been frequently utilized to modulate the properties of VO2. However, strain is usually harmful to the mechanical behavior of films and will possibly accelerate the performance deterioration, which is not wanted in many cases. In this work, fluorophlogopite mica has been used as a substrate for van der Waals epitaxy of VO2 films. The fabricated VO2/mica sample shows excellent flexibility and prospective phase-transition performances. More importantly, VO2 films with various thicknesses grown on mica exhibit almost strain-free state and show stable phase-transition temperatures during the SMT. In comparison, VO2 films grown on c-cut sapphires were effectively modulated by the strain effect and show strong thickness-dependent phase-transition temperatures. We have also studied the differences in SMT properties such as the amplitude of the phase transition and hysteresis width. The strain-free thin-film technology reported in this work is anticipated to be beneficial in the fabrication of reliable and flexible phase change devices utilizing VO2/mica thin films.