The influence of post-annealing on the chemical structures and dielectric properties of the surface layer of Ba0.6Sr0.4TiO3 films

Barium strontium titanate (Ba0.6Sr0.4TiO3, BST) films have been deposited on Pt/Ti/SiO2/Si substrates by radio frequency magnetron sputtering. The influences of conventional thermal annealing (CTA) and rapid thermal annealing (RTA) on the chemical structures of the surface layers of the BST films have been investigated. Grazing x-ray diffraction and atomic force microscopy show that the RTA-films exhibit more compact structure and more completed crystallization than the CTA-films. X-ray photoelectron spectroscopy (XPS) investigations show that the surface layer is composed of a non-perovskited BST phase and a perovskited BST phase. For the CTA-film, the surface contains about 70% non-perovskited BST phase, and the surface layer is approximately 3-5 nm thick, while for the RTA-film, the surface non-perovskited BST phase amounts to about 40%, and the surface layer is about 1nm. XPS also indicates that the CTA-film surface adsorbs a larger amount of carbon contaminations than the RTA-film. Fourier transform infrared reveals that the amount of the surface adsorbed water and/or OH groups may be ignored. The non-perovskited BST phase is mainly related to the surface structure and the adsorbed carbon contaminations. The effect of annealing temperature on the surface layer and the amount of non-perovskited BST phase has been discussed, and the dielectric properties have also been measured.