A Comparative Study on the Diffusion Behaviors of Metal and Oxygen Ions in Metal-Oxide-Based Resistance Switches via ab Initio Molecular Dynamics Simulations

Wedig et al.’s recent experiment (Wedig, A.; Nature Nanotech. 2016, 11, 67.) revealed that the diffusion of both metal (M) and O ions occurs in MOx-based resistance switches. However, the diffusion mechanism and the competition between the diffusion of M and O ions during switching processes are still unclear. In this work, taking amorphous TaOx and HfOy as examples, we have studied the diffusion behaviors of Ta/Hf and O ions by using extensive molecular dynamics simulations. Our results reveal that the mobilities of Ta/Hf ions increase and approach those of O ions with the decrease of O content, which is attributed to the changes in M/O coordination numbers and M–O/M–M bond strength. Interestingly, in the conductive filament region, the mobilities of Ta (or Hf) ions are comparable to (or less significant than) those of O ions, and thus, the diffusion of both Ta and O ions takes important roles in the TaOx-based device, whereas O ion diffusion is predominant in the HfOy-based device, even though Hf ions are mobile