Composition-related effects of microstructure on the ferroelectric behavior of SBT thin films

Non-stoichiometric strontium bismuth tantalate, Sr1−xBi2+yTa2O9 (SBT) thin films with different cation ratios have been deposited by metalorganic decomposition (MOD) on Pt/TiO2/SiO2/Si(1 0 0) substrates, using strontium (2,2,6,6-tetramethyl-3,5-heptadionate), bismuth (2,2,6,6-tetramethyl-3,5-heptadionate), and tantalum ethoxide as precursors. Crystallization of the films was carried out at 750°C under an atmosphere of O2, following a firing step at 550°C. The crystal phase and orientation of the 300 nm thick films were studied by XRD (CBXRD and GIXRD). The surface morphology of the films was examined by AFM. For an Sr:Bi ratio of 0.8:2.2, the films are formed by large clusters of elongated grains corresponding to the SBT phase embedded in a matrix of a Bi-deficient pyrochlore phase. For Sr:Bi ratios of 0.7:2.2 and 0.7:2.3, we obtained single-phase orthorhombic SBT films formed by densely packed elongated grains, whose axial ratio was dependent on the specific cation ratio used. Single-phase SBT films showed very low polarization fatigue after 1011 switching cycles and good retention properties.