Ferroelectric property of a-/b-axis-oriented epitaxial Sr_0.8Bi_2.2Ta₂O₉ thin films grown by metalorganic chemical vapor deposition

In this study, a-/b-axis-oriented epitaxial Sr_0.8Bi_2.2Ta₂O₉ (SBT) thin films were grown on (101)TiO₂ and (101)RuO₂//(110)Al₂O₃ substrates by metalorganic chemical vapor deposition (MOCVD). By several X-ray diffraction techniques, the a-/b-axis-oriented epitaxial growth on the substrate with a rutile structure was confirmed. The leakage current density of SBT was characterized along the a-/b-axis and c-axis, and the lower defect density in the pseudoperovskite layer was revealed by comparison with Bi₄Ti₃O₁₂. The saturation polarization (Ps), remanent polarization (Pr), and coercive field (Ec) were 6.0μC/cm₂, 3.1μC/cm₂ and 54 kV/cm, respectively. The estimated spontaneous polarization along the a-axis corrected by the a-/b-domain volume ratio was 20μC/cm2, which is identical to previously estimated values. The switching charge versus the repetitive 1.2×10¹⁰ switching cycles remained almost constant, indicating a superior fatigue endurance along the direction parallel to the (Bi₂O₂)²⁺ layer.