Metal dopants in HfO₂-based RRAM: first principle study

Based on density-functional theory (DFT), the effects of metal dopants in HfO₂-based RRAM are studied by the Vienna ab initio simulation package (VASP). Metal dopants are classified into two types (interstitial and substitutional) according to the formation energy when they exist in HfO₂ cell. Several conductive channels are observed through the isosurface plots of the partial charge density for HfO₂ doped with interstitial metals, while this phenomenon cannot be found in HfO₂ doped with substitutional metals. The electron density of states (DOS) and the projected electron density of states (PDOS) are calculated and analyzed; it is found that the conduction filament in HfO₂ is directly formed by the interstitial metals and further, that the substitutional metals cannot directly generate conduction filament. However, all the metal dopants contribute to the formation of the oxygen vacancy (V_O) filament. The formation energy of the V_O and the interaction between metal dopants and V_O are calculated; it is revealed that the P-type substitutional metal dopants have a strong enhanced effect on the V_O filament, the interstitial metal dopants have a minor assistant effect, while Hf-like and N-type substitutional metal dopants have the weakest assistant effect.