Microstructure dependent switching properties of VO 2 thin films

Abstract

Vanadium dioxide (VO 2) thin films with different microstructure and orientations were deposited on sapphire and MgO substrates using pulsed laser deposition technique (PLD). X-ray diffraction (XRD), scanning probe microscopy (SPM), resistivity, and spectrophotometry measurements were used to analyze the effect of microstructure and orientation on the metal–insulator transition (MIT) characteristics of the films in order to optimize film properties for IR wavelength optical shutters. Films with five different epitaxial in plane orientations including (1 0 0), (0 0 1), (0 2 0), (0 1 1), and (1 1 1), and polycrystalline films were deposited by varying substrate orientation and partial oxygen pressure. Depending on the crystal orientation, microstructure, and thickness, films performed 3–4 decades MIT in resistivity with varying transition temperatures and hysteresis loop widths. Metal state transmittance at the wavelength of 1.5 μm as low as 0.1% was measured leading to optical density of OD λ ≈ 10 5. Steepest transitions and narrow hysteresis loops were found in the films with lowest lattice misfit strain and in the polycrystalline structures, where residual macroscopic stress was relaxed due to cracking.