Study of a charge transition-driven resistive switching mechanism in TiO 2 -based random access memory via density functional theory.

The nature of the conducting filament (CF) with a high concentration of oxygen vacancies (V O s) in oxide thin film-based resistive random access memory (RRAM) remains unclear. The V O s in the CF have been assumed to be positively charged (V O 2+ ) to explain the field-driven switching of RRAM, but V O 2+ clusters in high concentration encounter Coulomb repulsion, rendering the CF unstable. Therefore, this study examined the oxidation state of V O s in the CF and their effects on the switching behavior via density functional theory calculations using a Pt/TiO 2 /Ti model system. It was concluded that the V O s in the CF are in a low oxidation state but are transformed to V O 2+ immediately after release from the CF. In addition, the short-range interactions between V O s were confirmed to facilitate the rupture and rejuvenation of the CF by reducing the required activation energy. Finally, an improved switching model was proposed by considering the charge transition of V O s, providing a plausible explanation for the reported coexistence of two opposite bipolar switching polarities: the eight-wise and the counter-eight-wise polarities.