Variation of electrical properties of Sr_0.8Bi _2+XTa₂O_9+δ ferroelectric thin films with bismuth content

In this work, we have investigated the effect of bismuth content on electrical properties of Sr_0.8Bi_2-xTa₂O _9+δ (SBT) thin films, obtained by using the metallorganic decomposition technique. The SBT precursor solution was prepared using high purity strontium acetate, bismuth acetate and tantalum ethoxide as the starting materials and acetic acid as the solvent. Thin films were deposited on Ir(50nm)/SiO₂(100nm)/Si substrates by spin coating with precise control of the solution viscosity and spin speed. As-deposited films were dried at 150°C for 10 min followed by pyroiysis at 400°C for 30 min in static air to remove the solvent and organic impurities. The films were then post-annealed at 650°C for 30 min in ambient oxygen atmosphere. The crystallinity of SBT thin films containing various bismuth levels was characterized by X-ray diffraction (XRD). The 30% Bi excess SBT thin films exhibited preferentially (115) oriented phase. The XRD pattern showed all major peaks corresponding to SBT phase. The microstructure, P-E hysteresis loops and leakage current of SBT films were found to be dependent on the bismuth content.