Oxygen Vacancies Control Transition of Resistive Switching Mode in Single-Crystal TiO2 Memory Device.

Epitaxial TiO2 thin films were grown by radio-frequency magnetron sputtering on conductive Nb-SrTiO3 substrates. X-ray photoelectron spectroscopy reveals that the oxygen vacancies inside the TiO2 films can be dramatically reduced by postannealing treatment under an oxygen atmosphere. The decreasing concentration of oxygen vacancies modifies the resistive switching (RS) mechanism from a valence change mode to a electrochemical metallization mode, resulting in a high switching ratio (≥105), a small electronic leakage current in the high-resistance (≥109 Ω) state, and a highly controlled quantized conductance (QC) in the low-resistance state. These results allow for understanding the relationship between different RS mechanisms as well as the QC for multilevel data storage application.