Atomic layer deposition of ferroelectric bismuth titanate Bi4Ti3O12 thin films

Bismuth titanate thin films were prepared by atomic layer deposition. Bismuth tris(bis( trimethylsilyl)amide) Bi(N(SiMe3)(2))(3) was used as the bismuth and titanium methoxide Ti(OMe)(4) as the titanium precursor while water was used as the oxygen source. Self-limited growth of Bi-Ti-O films took place at a deposition temperature of 190 degrees C. The as-deposited Bi-Ti-O films showed surface morphologies atypical for amorphous ALD films, which may point either to partial bismuth reduction or to weak ordering of the deposited Bi-Ti-O during film growth. The Bi-Ti-O films postannealed at 750 degrees C crystallized to either pyrochlore Bi2Ti2O7-type structures, mixtures of the pyrochlore- and layered perovskite Bi4Ti3O12 phases, or phase-pure Bi4Ti3O12 depending on the Bi/(Bi + Ti) ratio in the film. Slightly Bi-rich films were found to result in the phase-pure Bi4Ti3O12. After postannealing in O-2 at 600 degrees C 51 nm thick films deposited on Pt/SiO2/Si substrates had a remanent polarization P-r and coercive field E-c of 0.5 mu C/cm(2) and 24 kV/cm, respectively. The leakage current density was below 1 mu A/cm(2) up to +/- 1.6 V applied bias.