Investigations on the infrared optical properties of BaTiO₃ ferroelectric thin films by spectroscopic ellipsometry

BaTiO₃ thin films have been grown directly on Pt (111)/Ti/SiO₂/Si (100) substrates by a modified sol-gel method. X-ray diffraction analysis shows that the BaTiO₃ thin films are polycrystalline. The infrared optical properties of the thin films are investigated using the infrared spectroscopic ellipsometry (IRSE) in the spectral range of 2.5-12.5 μm. By fitting the measured ellipsometric parameter (tan Ψ and cos Δ) data with a three-phase model (air/BaTiO₃/Pt), and a derived classical dispersion relation for the thin films, the optical constants and thickness of the thin films have been simultaneously obtained. The refractive index decreases, and the extinction coefficient increases with increasing wavelength. Accordingly, the absorption coefficient increases as the wavelength increases. The absorption of the Ni/BaTiO₃/Pt multilayer thin films has been calculated and the values in this study are larger than that of the Ni/PZT/Pt structure reported. Finally, the effective static charge obtained is smaller than it would be in a purely ionic material for the BaTiO₃ thin films.