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(SiMe 3 ) 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 °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 °C crystallized to either pyrochlore Bi 2 Ti 2 O 7 -type structures, mixtures of the pyrochlore- and layered perovskite Bi 4 Ti 3 O 12 phases, or phase-pure Bi 4 Ti 3 O 12 depending on the Bi/(Bi + Ti) ratio in the film. Slightly Bi-rich films were found to result in the phase-pure Bi 4 Ti 3 O 12 . After postannealing in O 2 at 600 °C 51 nm thick films deposited on Pt/SiO 2 /Si substrates had a remanent polarization P r and coercive field E c of 0.5 μC/cm 2 and 24 kV/cm, respectively. The leakage current density was below 1 μA/cm 2 up to ±1.6 V applied bias.