Thermal desorption spectroscopy of (Ba, Sr)TiO3 thin films prepared by chemical vapor deposition

Thermal desorption characteristics of (Ba,Sr)TiO3 [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 CO2 at 400 degrees C and 900 degrees C, and CO at 600 degrees C. The intensities of the CO2 peaks at 400 degrees C and 900 degrees 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 CO2 peak at 900 degrees C may originate from BaCO3 and/or SrCO3 lumps formed in the films, and the CO2 peak at 400 degrees C may be attributed to gases adsorbed on the sites of contaminants such as BaOx and/or SrOx in films, due to excess Ba and Sr coming from the atmosphere after deposition. On the other hand, the CO peak at 600 degrees C occurred most strongly from BST films with high dielectric constants at (Ba+Sr)/Ti similar to 1, or perovskite crystalline structures having large grains. Moreover, the desorption of CO at 600 degrees C was also observed from films kept in the atmosphere after annealed above 600 degrees C in vacuum. These results imply that the BST crystalline perovskite grains may have adsorption sites for CO from the atmosphere.