Thermal Desorption Spectroscopy of (Ba, Sr)TiO₃ Thin Films Prepared by Chemical Vapor Deposition

Abstract

Thermal desorption characteristics of (Ba, Sr)TiO 3 [BST] thin films prepared by metalorganic chemical vapor deposition (CVD) using liguid sources have been studied, together with their crystallinity and electrical properties. Thermal desorption was observed for CO 2 at 400° C and 900° C, and CO at 600° C. The intensities of the CO 2 peaks at 400° C and 900° C increased with the increasing atomic composition ratio of (Ba+Sr)/Ti, in relation to the excess Ba and Sr in the BST films; in particular, the CO 2 peak at 900° C may originate from BaCO 3 and/or SrCO 3 lumps formed in the films, and the CO 2 peak at 400° C may be attributed to gases adsorbed on the sites of contaminants such as BaO x and/or SrO x in films, due to excess Ba and Sr coming from the atmosphere after deposition. On the other hand, the CO peak at 600° C occurred most strongly from BST films with high dielectric constants at (Ba+Sr)/Ti∼1, or perovskite crystalline structures having large grains. Moreover, the desorption of CO at 600° C was also observed from films kept in the atmosphere after annealed above 600° C in vacuum. These results imply that the BST crystalline perovskite grains may have adsorption sites for CO from the atmosphere.