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 u sing high-resolution transmission electron microscopy and quantitative spec trum 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 sig nificant increase in Ti/Ba ratio as compared to the grain interiors. The re sults suggest that the deviations of Ti/(Ba + Sr) ratio from the stoichiome tric value of unity are accommodated by the creation of Ba/Sr vacancies, wh ich segregate to the grain boundary regions. The films with Ti contents equ al 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 dro p in dielectric permittivity accompanying increases in the Ti/(Ba + Sr) rat io.