Atomic Layer Deposition of oriented nickel titanate (NiTiO3)

The combination of the two well behaved binary oxide ALD processes, NiO (Ni(acac)2 + O3) and (TiO2 (TiOiPr)4 + H2O), provide excellent means for depositing thin films of NixTi1−xOy with highly controllable stoichiometry. In particular, stoichiometric NiTiO3 was obtained for a 1:1 molar pulsing ratio of NiO:TiO2. An ALD window was observed between 175 and 275 °C for this composition, within which the growth rate remained unchanged at ∼43 pm/subcycle. The measured refractive index was 2.42 and a direct band gap of 2.27 eV was found. The described process yielded smooth (0.4-0.9 nm RMS roughness), crystalline films of NiTiO3 as-deposited on Si (1 0 0) substrates, with a strained (0 0 1) orientation. Annealing at 650 °C for 15 min relaxed the strain and improved the crystallinity.