VO2 thin films deposited on silicon substrates from V2O5 target : Limits in optical switching properties and modeling

• Published in: Thin solid films 2008-01, Vol.516 (6), p.891-897
• Main Authors: SAITZEK, Sébastien, GUINNETON, Frédéric, GUIRLEO, Guillaume, SAUQUES, Laurent, AGUIR, Khalifa, GAVARRI, Jean-Raymond
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Composition and phase identification; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Material chemistry; Optical materials; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Optics; Physics; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2007.04.129

Thermochromic VO2 thin films presenting a phase change at Tc = 68 °C and having variable thickness were deposited on silicon substrates (Si-001) by radio-frequency sputtering. These thin films were obtained from optimized reduction of low cost V2O5 targets. Depending on deposition conditions, a non-thermochromic metastable VO2 phase might also be obtained. The thermochromic thin films were characterized by X-ray diffraction, atomic force microscopy, ellipsometry techniques, Fourier transform infrared spectrometry and optical emissivity analyses. In the wavelength range 0.3 to 25 μm, the optical transmittance of the thermochromic films exhibited a large variation between 25 and 100 °C due to the phase transition at Tc: the contrast in transmittance (difference between the transmittance values to 25 °C and 100 °C) first increased with film thickness, then reached a maximum value. A model taking into account the optical properties of both types of VO2 film fully justified such a maximum value. The n and k optical indexes were calculated from transmittance and reflectance spectra. A significant contrast in emissivity due to the phase transition was also observed between 25 and 100 °C.