Microstructure and chemistry of nonstoichiometric (Ba,Sr)TiO3 thin films deposited by metalorganic chemical vapor deposition

The microstructure and chemistry of (Ba,Sr)TiO3 thin films deposited on Pt/SiO2/Si substrates by metalorganic chemical Vapor deposition were studied using high-resolution transmission electron microscopy and quantitative spectrum imaging in electron energy loss spectroscopy. The grain boundaries in all films with overall Ti content ranging from 50.7% to 53.4% exhibit a significant increase in Ti/Ba ratio as compared to the grain interiors. The results suggest that the deviations of Ti/(Ba + Sr) ratio from the stoichiometric value of unity are accommodated by the creation of Ba/Sr vacancies, which segregate to the grain boundary regions. The films with Ti contents equal to or greater than 52% additionally contained an amorphous Ti-rich phase at some grain boundaries and multiple grain junctions; the amount of this phase increases with increasing overall Ti content. The analysis indicates that the amorphous phase can only partially account for the significant drop in dielectric permittivity accompanying increases in the Ti/(Ba + Sr) ratio.