First-principles study of Tungsten atoms on Hafnia/Platinum and Hafnia/Graphene interfaces under the high temperature environments.

Recently, memristive devices at a record-high operating temperatures have been achieved by replacing the platinum (Pt) electrode by graphene (Gr) in a memristor consisting of tungsten (W)/HfO₂/Pt layers. The superior high temperature stability of W/HfO₂/Gr memristor over W/HfO₂/Pt is attributed to higher barriers for W-filament formation on the Gr surface than on the Pt surface. To test hypothesis, we computed adsorption energies and diffusion coefficients of W on the Gr and on the Pt(111) surfaces. The adsorption energies of W atoms on the Pt(111) surface are lower than those on the Gr surface. On the Pt(111) surface, two W atoms tend to be more stable when adsorbed separately rather than close to each other. In contrast, on the Gr surface, W atoms tend to form W dimers, and at temperatures around 1,300 K, they are likely to desorb as a dimer easily from the surface. Regarding diffusion, W atoms diffuse much faster on the Pt(111) than on the Gr. These findings suggest that, on the Gr surface, W filaments are unlikely since W dimers desorb easily. On the Pt(111) surface, W atoms tend to avoid close proximity, they diffuse easily while staying on the surface, favoring larger filament formation.

In this presentation, we will discuss the results of high temperatures simulations.