Atomistic mechanisms of copper filament formation and composition in Al₂O₃-based conductive bridge random access memory

Conductive filament formation and composition in Oxide-based Conductive Bridge Random Access Memory (CBRAM) are investigated. To this end, Al₂O₃/Cu-based CBRAM is electrically characterized and studied. Current-voltage characteristics exhibit different forming behaviors depending on device polarization exposing the charged species involved during the forming process. In order to get more insights at the microscopic level, ion diffusion is investigated in depth by first-principles calculations. We study different point defects in Al₂O₃ which can come either from the post-process of the material itself or after top electrode deposition or during device operation. Since the role of Oxygen Vacancies (V_O) and Copper (Cu) ions is core to the switching mechanism, ab initio calculations focus on their displacements. For different charge states in Al₂O₃, we extract the thermodynamic and activation energies of Cu, Te, Al, and O related point defects. The results reveal that Cu is not the only ion diffusing in the Al₂O₃-based CBRAM switching mechanism while Te ions appear unfavorable. A Cu/V_O based hybrid filament model is proposed, and the impact of Aluminum Vacancies (V_Al) on the forming process is demonstrated.