Grain-oriented ferroelectric bismuth titanate thin film prepared from acetate precursor

Bismuth titanate (Bi₄Ti₃O₁₂) thin films were fabricated by a spin coating deposition and rapid thermal processing (RTP) technique. The acetate-derived solution for deposition was synthesized by blending dissolved bismuth acetate in aqueous acetic acid and then adding titanium acetate. A series of electrically insulating, semiconducting and conducting substrates were evaluated for Bi₄Ti₃O₁₂ films deposition. X-ray diffraction indicated that the initial crystallization temperature of the Bi₄Ti₃O₁₂ films was 500°C or less; a 700°C crystallization treatment was used to obtain single phase films. The Bi₄Ti₃O₁₂ film crystallographic orientation is shown to depend on three factors: substrate type; number of coating layers; and thermal processing. While preferred c-direction orientation was observed for films deposited on silver foil substrates, preferred a-direction orientation was obtained for films deposited on both Si and Pt coated Si wafers. The films were dense, smooth, crack-free and had grain sizes ranging from 20 to 400 nm. Film thickness and refractive index were determined using a combination of ellipsometry, waveguide refractometry and TEM techniques. The refractive index is close to the value of single crystal BIT.