Optimal migration path of Ag in HfO₂: A first-principles study

First-principles calculations are used to investigate the migration path of Ag in the HfO₂-based resistive random access memory (ReRAM). The formation energy calculation suggests that there are two different sites (site 1 and site 3) for the incorporation of Ag atoms into the HfO₂ unit cell. Thermodynamic analysis shows that the motion of Ag atom in the HfO₂ supercell appears to be anisotropic, which is due to the fact that the Ag atom at site 3 moves along the 111 orientation, but the Ag atom at site 1 moves along the 001 orientation. The migration barriers of the Ag atoms hopping between neighboring unit cells are calculated along five different orientations. Difficulty in producing motion of the Ag atom varies with the migration barrier: this motion is minimized along 111 orientation. Furthermore, The optimal circulation path for Ag migration within the HfO₂ supercells is obtained, and is found to be approximately along the 111 orientation. Therefore, it is proposed that the positive voltage should be applied along this orientation, the conduction filament may form more easily, which could improve the response time and reduce the power consumption in ReRAM applications.