Effect of Charge Injection on the Conducting Filament of Valence Change Anatase TiO2 Resistive Random Access Memory Device.

The recent observation of stable quantized conductance in anatase TiO2 resistive random access memory (ReRAM) devices opens up a new pathway toward the realization of brain-inspired neuromorphic computing devices. Herein, for the first time, ab initio calculations are implemented to understand the resistive switching phenomena in anatase TiO2. Oxygen vacancy configurations with different charge states are studied to gain insight into the ON and OFF states of ReRAM devices. Among the trivacancy configurations, the Vo+ state is observed to induce highly dispersed defect states within the bandgap forming a charge density channel where the carriers behave as free electrons leading to the formation of a conducting filament (CF). On the contrary, the breakdown of the CF is noticed by the removal of an oxygen vacancy from the trivacancy configuration. In this OFF state, the defect state carriers are found to be highly localized. In addition, we have also investigated the effect of charge injection on the crystal field symmetry of the CF. The reduction of symmetry due to the trivacancy configuration lowers the eg manifold energy, whereas the divacancy configuration lowers the t2g manifold energy.