Oxygen stability and leakage current properties of La-modified bismuth titanate ferroelectric thin films

The effects of oxygen annealing on the structural properties and leakage current behaviors of sol-gel-derived Bi_{3 25}La_0.75Ti ₃O_12-y ferroelectric thin films have been studied. The thin films were pyrolyzed in different atmospheric conditions including a fully oxygenized ambient of 1 bar and an evacuated ambient of less than 10 mbar. X-ray diffraction patterns of the deoxygenated films showed measurable shifts to a higher angle, indicating that each deoxygenated film had a smaller lattice constant than the oxygenated one. Scanning probe analysis showed well-developed grains and inhomogeneous and asymmetric bound charges in both samples. The leakage current behavior of the films was measured as a function of voltage and temperature and was explained on the basis of the Schottky-Simmons thermionic emission model. X-ray photoemission spectra showed that oxygen stability in Bi₂O₂ layers plays an important role in determining the level of leakage current in the films.