Structural Characterization of Atomic Layer Deposited Vanadium Dioxide

Vanadium dioxide (VO 2 ) is a promising smart material particularly appealing for added functionality in both electronic and optical applications. We investigate the structure of VO 2 films fabricated using atomic layer deposition (ALD) on c-Al 2 O 3 substrates and the structure of the same VO 2 films after an optimized anneal for 2 h at 585 °C in 10 –5 Torr O 2 . Synchrotron-based grazing incidence X-ray diffraction (GIXRD) measurements revealed that the as-deposited ALD VO 2 contains small crystalline inclusions of both V 2 O 5 and VO. Ex situ annealing of the ALD VO 2 film results in formation of mixed phase VO 2 (predominantly M1 with indications of a small amount of M2), with a twinned monoclinic structure that is highly oriented and lattice matched to the c-Al 2 O 3 substrate. Using in situ temperature-dependent measurements, the M1 and M2 components were shown to transition across different temperature ranges, which could account for the hysteretic behavior seen in these VO 2 thin films. Additionally, these high-quality crystalline VO 2 films exhibit a 50% transmission modulation at a wavelength of 2 μm, with only a 35 nm thick VO 2 film.