THERMAL-DESORPTION SPECTROSCOPY OF (BA, SR)TIO3 THIN-FILMS PREPARED BY CHEMICAL-VAPOR-DEPOSITION

Thermal desorption characteristics of (Ba,Sr)TiO3 [BST] thin films pre pared by metalorganic chemical vapor deposition (CVD) using liguid sou rces have been studied, together with their crystallinity and electric al 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 C O2 peaks at 400 degrees C and 900 degrees C increased with the increas ing 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, an d 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 e xcess Ba and Sr coming from the atmosphere after deposition. On the ot her 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 p erovskite crystalline structures having large grains. Moreover, the de sorption of CO at 600 degrees C was also observed from films kept in t he atmosphere after annealed above 600 degrees C in vacuum. These resu lts imply that the BST crystalline perovskite grains may have adsorpti on sites for CO from the atmosphere.