Study of VO2 thin film synthesis by atomic layer deposition. (June 2019)

• Record Type: Journal Article
• Authors: Prasadam, V.P.; Dey, B.; Bulou, S.; Schenk, T.; Bahlawane, N.
• Is Part Of: Materials today chemistry. Volume 12(2019)
• Page Start: 332
• Page End: 342
• Publication Date: 2019-06
• Subjects: ALD -- Vanadyl triisopropoxide -- Vanadium dioxide -- Semiconductor-to-metal transition; Chemistry -- Periodicals; Materials -- Research -- Periodicals; Materials science -- Periodicals; Chemistry; Materials -- Research; Electronic journals; Periodicals; 660.282
• DOI: 10.1016/j.mtchem.2019.03.005
• Languages: English
• ISSNs: 2468-5194

Abstract

Abstract: Vanadium dioxide emerges as an appealing material for smart thermal management and electrical/optical switching owing to its abrupt semiconductor-to-metal transition (SMT) at near room temperature. The application potential of this material should be leveraged by the implementation of the atomic layer deposition (ALD), a method that enables an unequaled control over the thickness and film conformality on complex substrate structures by virtue of self-limiting growth mechanism. Here, the vanadium oxide thin films are synthesized from vanadyl (V) triisopropoxide (VTOP) as the vanadium precursor and H2 O as the reactant. The thermal decomposition threshold of VTOP was observed at 90 °C, and temperature window with a constant growth rate was observed at 50–90 °C. The saturation behavior of the ALD half reactions was demonstrated at 80 °C, yielding the optimized ALD cycle conditions of 8 s VTOP/15 s purge/6 s H2 O/15 s purge with a growth rate of 0.047 nm/cycle. The as-grown amorphous films convert into VO2 via a 4-h heat treatment under 10 −5 mbar at 550 °C. The formed VO2 features a sudden and reversible change in the total hemispherical reflectance in UV-VIS-NIR region at 68 °C, confirming its SMT behavior. The conversion process induces, however, a surface roughening, which was considerably suppressed by a postdeposition treatment in plasma environment prior the annealing treatment. Highlights: Vanadium oxide atomic layer deposition is performed via the thermal hydrolysis of vanadyl triisopropoxide (VTOP) at 50–90 °C. The VTOP thermolysis is revealed at and above 100 °C. Highly conformal vanadium oxide is reported on carbon nanotubes. Heat treatment at 550 °C yields VO2 with a strong semiconductor-to-metal transition behavior. Plasma and thermal treatments yield VO2 with low impact of the surface morphology.