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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.512

Vanadium Oxide Thin Film by Aqueous Spray Deposition Seth Calhoun1, Rachel Evans1, Cameron Nickle1, Isaiah O. Oladeji2, Justin Cleary3, Evan M Smith3, Sayan Chandra1, Debashis Chanda1, Robert E. Peale1

1

Physics Department, University of Central Florida, Orlando, FL, United States.

2

SISOM Thin Films LLC, 1209 W. Gore St. Orlando FL 32805

3

Air Force Research Laboratory, Sensors Directorate, Wright-Patterson AFB, OH, United States.

ABSTRACT

Vanadium Oxide has application to infrared bolometers due to high temperature coefficient of resistivity (TCR). It has attracted interest for switchable plasmonic devices due to its metal to insulator transition near room temperature. We report here the properties of vanadium oxide deposited by an aqueous spray process. The films have a ropy surface morphology with ~70 nm surface roughness. The polycrystalline phase depends on annealing conditions. The films have TCR of ~2%/deg, which compares well with sputtered films. Only weak evidence is found for an insulator-metal phase transition in these films.

INTRODUCTION Vanadium Oxide and its different oxidation states have value in opto-electronic devices due to their electrical and optical properties. Semiconducting VO x with x~2 is well established for infrared bolometers due to its high TCR. VO 2 exhibits a strong resisitivity change with hysteresis that occurs at its semiconductor-metal phase transition near 60 C [2], which is particularly interesting for switchable plasmonic devices. Below this phase transition, the material is semiconducting with a negative TCR. Above, it is metallic with positive TCR. The resistivity drops abruptly by ~100-fold as the temperature passes through the transition from below. The VOx used for bolometers has the negative room temperature TCR of about -2%/C, but lacks the phase transition [1].

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VOx is typically deposited by vacuum-based methods, which include reactive sputtering of a vanadium target in a partial oxygen environment [3][4], evaporation [5], and pulsed laser deposition [6]. For lower manufacturing costs, a non-vacuum process would be preferable. This paper reports on the properties of vanadium oxide films deposited by an aqueous spray method.

EXPERIMENTAL METHODS Vanadium oxide (VOx) films were grown on glass substrates by an aqueous spray method known as Streaming Process for Electrodeless Electrochemical Deposition (SPEED) [10]. The deposition apparatus is manufactured by SISOM Thin Films LLC. Precursors comprised 0.1 M ammonium metavanadate in a mixture of deionized water and organic solvents/ligand. Water (70% by volume) acts as a solvent and as the source of oxygen and the surface-attached nucleation sites for heterogeneous reaction. The ammonia and organic