The annealing temperature dependent integrity of Sr0.8Bi2Ta2O9 (SBT) on ultra-thin 4 nm SiO2 and Al2O3 buffered Si was investigated in this work. Although the capacitance-voltage characteristics show hysteresis loops in both cases, the memory window of Sr0.8Bi2Ta2O9/Al2O3 capacitor is larger than that of Sr0.8Bi2Ta2O9/SiO2 capacitor. As increasing annealing temperature from 800 to 900°C, the grain size and memory window of polycrystalline SBT increase both cases. At 800°C, the leakage current density of Sr0.8Bi2Ta2O9/Al2O3 capacitor is 3.2×10-8 A/cm2 at -3 V, which is low enough for deep sub-μm application. With increasing temperature to 900°C, the leakage current in both structures becomes smaller.