Strong oxygen pressure dependence of ferroelectricity in BaTiO ₃/SrRuO₃/SrTiO₃ epitaxial heterostructures

The oxygen pressure effect on the structural and ferroelectric properties have been studied in epitaxial BaTiO₃ (BTO)/SrRuO₃/ SrTiO₃ (001) heterostructures grown by pulsed laser deposition. It is found that oxygen pressure is a sensitive parameter, which can influence the characteristics of oxide films in many aspects. The out-of-plane lattice parameter, tetragonality, (c/a) and Ti/Ba ratio monotonously decrease as the oxygen pressure increases from 5 mTorr to 200 mTorr. Microstructural study shows that the growth of BaTiO₃ varies from a dense large grained structure with a smooth surface to a small columnar grain structure with rough surface as the deposition pressure increases. Electrical measurements show that the 40 mTorr deposited BTO films present maximum remanent polarization (P _r) (14 μC/cm²) and saturation polarization (P _s) (27 μC/cm²) due to the stoichiometric cation ratio, very smooth surface, and low leakage current. These results demonstrate that the controlling of cation stoichiometry, surface morphology, and leakage current by oxygen pressure is one of very important prerequisites for device applications in the BaTiO₃ films.