The mechanism for the suppression of leakage current in high dielectric TiO_2 thin films by adopting ultra-thin HfO_2 films for memory application

摘要

The electrical leakage current of thin rutile structured TiO_2 films deposited by atomic layer deposition on a Ru electrode was enormously reduced by depositing an extremely thin HfO_2 (＜1 nm) on top.The sacrifice of the capacitance density by the HfO_2 was minimized.The leakage mechanism analysis on the Pt/TiO_2/Ru and Pt/HfO_2/TiO_2/Ru structures revealed that the improvement in leakage current was attributed to the reduction of defect (trap) density in the TiO_2 film.The interfacial potential barrier height for electron transport in thinner (~ 10 nm) TiO_2 films was lower than that of thicker (~ 20 nm) TiO_2 films,which resulted in a higher leakage current in these films.The capping of ultra-thin (~ 0.7 nm) HfO_2 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.