Controlling the initial growth behavior of SrTiO₃ films by interposing Al₂O₃ layers between the film and the Ru substrate

The effects of thin Al₂O₃ layers interposed between atomic layer deposited SrTiO₃ (STO) films and Ru substrates on the growth and properties of STO films were examined. Although a 3-4 nm thick TiO₂ barrier layer was necessary to completely suppress the oxygen diffusion from the underlying Ru(O) layer, which could result in uncontrolled excessive Sr incorporation into the film, a 2-3 nm thick Al₂O ₃ barrier layer was sufficient to achieve the saturated oxygen blocking effect. Therefore, only a 0.4 nm thick Al₂O₃ layer could effectively suppress uncontrollable initial excessive incorporation of Sr, and a 1 nm thick Al₂O₃ layer had a blocking effect that was equivalent to that of a 3 nm thick TiO₂ layer. STO films were crystallized in situ by the assistance of crystallized 2-3 nm thick STO seed layers that were pre-deposited and annealed. The bulk dielectric constant of STO calculated by the slope of equivalent oxide thickness vs. physical thickness was 173 on the 1 nm thick Al₂O₃/Ru substrate. However, further research is necessary to reduce the adverse contribution of the interfacial layers to achieve a scaling of the equivalent oxide thickness to ≪0.5 nm.