Compositional, structural and electrical characterization of barium titanate thin films prepared on fused silica and Si(111) by spray pyrolysis

Abstract

Barium titanate thin films have been prepared by chemical spray pyrolysis. Aqueous spray solutions of titanium isopropoxide and barium acetate, equimolar with respect to titanium and barium, were used as precursors. Deposition was carried out at a substrate temperature of 250°C. As-deposited films are amorphous. Films of BaTiO 3 (perovskite) were obtained by calcination in air to 600°C for various hours. Perovskite films are compact and smooth, according to their morphological aspect studied by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) combined with 4 keV Ar + depth profiling has shown that the as-deposited film corresponds to BaTiO 3 and that its composition stays constant through the whole film thickness. Residual carbon (in the form of BaCO 3 ) coming from the organic precursor solutions is only detected at the surface of the film, limited to the first atomic monolayers as revealed by depth profiling. Calcination in air at 600°C decreases this amount but BaCO 3 is still present at a percentage of 25% with respect to the whole amount of Ba in the film surface. Electrical characterization of a calcined BaTiO 3 film deposited on conductive n-type Si(111) was carried out with impedance spectroscopy in a frequency range of 10 Hz to 1 MHz. Assuming a film thickness of 100 nm as deduced by XPS depth profiling, the relative dielectric permittivity of our films can be estimated to be 80 at a frequency of 1 kHz.