High-Frequency Response in Ferroelectric BaSrTiO3 Thin Films Studied by Terahertz Time-Domain Spectroscopy

Abstract

We have measured the dielectric properties of BaTiO3–SrTiO3 thin films, deposited on fused silica substrates, in the MHz and THz frequency regions. Different experimental Chemical Vapor Deposition parameters were analyzed to improve dielectric properties of these thin films. In particular, we clarify pressure and oxygen percentages during the deposition of the thin layer. The complex permittivity function of the film was accurately determined between 100 GHz and 1 THz. We show that the real part of the dielectric behavior at very high frequencies follows the same tendency of the low frequency dielectric behavior also measured. These results are correlated to X-ray diffraction and RBS patterns, which show that the cationic ratio (Ba+Sr)/Ti increases from about 0.6 to 0.9 as sputtering pressure changes from 1 to 5 Pa, leading to better dielectric properties.