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

Epitaxial TiO 2 thin films were grown by radio-frequency magnetron sputtering on conductive Nb-SrTiO 3 substrates. X-ray photoelectron spectroscopy reveals that the oxygen vacancies inside the TiO 2 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 (≥10 5 ), a small electronic leakage current in the high-resistance (≥10 9 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.