Flexible VO2 films grown on ZnO-nanorod buffered polyimide sheets with large insulator metal transition: Evaluation of flexible performance

Abstract

We fabricated stand-alone flexible vanadium dioxide (VO2) films on 10 μm-thick polyimide (PI) sheets with large insulator metal transition (IMT). Zinc oxide (ZnO)-nanorods grown by the chemical synthesis method as a buffer layer between VO2 and PI realized IMT with resistance change nearly three orders of magnitude. Highly bm axis oriented VO2 films on ZnO_NR buffered PI realized switching of 1450 nm infrared-light more than 40%. The transmittance values at a metallic phase below 2% at temperatures higher than 70 °C were quite low, suggesting high potential for various applications in the infrared and terahertz wavelength region. Number densities of cracks in the VO2 films were estimated from the scanning electron microscopy (SEM) images. Quantitative relation between crack density and the bias voltage suggested the strain-induced formation of cracks in the VO2 films prepared by biased-sputtering. As for flexible performance, the stand-alone VO2 films on PI were directed to bending examinations up to 2000 times. The ZnO-nanorods buffered VO2 films on PI showed high durability for maintaining the superior IMT characteristics. The results obtained in this study show a way to realize practical flexibility of VO2 stand-alone sheets which are able to apply for a variety of fields utilizing switching of VO2.