Atomic layer deposition of VO2 films with Tetrakis-dimethyl-amino vanadium (IV) as vanadium precursor

摘要

VO2 thin films have been grown on Si(100) (VO2/Si) and fused silica substrates (VO2/SiO2) by atomic layer deposition (ALD) using tetrakis-dimethyl-amino vanadium (IV) (TDMAV) as a novel vanadium precursor and water as reactant gas. The quartz crystal microbalance (QCM) measurement was performed to study the ALD process of VO2 thin film deposition, and a constant growth rate of about 0.95 angstrom/cycle was obtained at the temperature range of 150-200 degrees C. XRD measurement was performed to study the influence of deposition temperature and post-annealing condition on the crystallization of VO2 films, which indicated that the films deposited between 150 and 200 degrees C showed well crystallinity after annealing at 475 degrees C for 100 min in Ar atmosphere. XPS measurement verified that the vanadium oxidation state was 4+ for both as-deposited film and post-annealed VO2/Si film. AFM was applied to study the surface morphology of VO2/Si films, which showed a dense polycrystalline film with roughness of about 1 nm. The resistance of VO2/Si films deposited between 150 degrees C and 200 degrees C as a function of temperature showed similar semiconductor-to-metal transition (SMT) characters with the transition temperature for heating branch (T-c,T-h) of about 72 degrees C, a hysteresis width of about 10 degrees C and the resistance change of two orders of magnitude. The increase of T-c,T-h compared with the bulk VO2 (68 degrees C) may be attributed to the tensile stress along the c-axis in the film. Transmittance measurement of VO2/SiO2 films showed typical thermochromic property with a NIR switching efficiency of above 50% at 2 mu m across the transition. (C) 2016 Elsevier B.V. All rights reserved.