The mechanism for the suppression of leakage current in high dielectric TiO₂ thin films by adopting ultra-thin HfO₂ films for memory application

The electrical leakage current of thin rutile structured TiO₂ films deposited by atomic layer deposition on a Ru electrode was enormously reduced by depositing an extremely thin HfO₂ (< 1 nm) on top. The sacrifice of the capacitance density by the HfO₂ was minimized. The leakage mechanism analysis on the Pt/TiO₂/Ru and Pt/HfO ₂/TiO₂/Ru structures revealed that the improvement in leakage current was attributed to the reduction of defect (trap) density in the TiO₂ film. The interfacial potential barrier height for electron transport in thinner (∼ 10 nm) TiO₂ films was lower than that of thicker (∼ 20 nm) TiO₂ films, which resulted in a higher leakage current in these films. The capping of ultra-thin (∼ 0.7 nm) HfO₂ films effectively increased the potential barrier height, and the leakage current was decreased accordingly. The leakage current behavior was systematically analyzed from quantum mechanical transport simulations.