Positive and negative dipole layer formation at high-k/SiO₂ interfaces simulated by classical molecular dynamics

We show the electric dipole layer formed at a high-k/SiO₂ interface can be explained by the imbalance between the migration of oxygen ions and metal cations across the high-k/SiO₂ interface. Classical molecular dynamics (MD) simulations are performed for Al₂O₃/SiO₂, MgO/SiO₂, and SrO/SiO₂ interfaces. The simulations qualitatively reproduce the experimentally observed flatband voltage (VFB) shifts of these systems. In the case of the Al₂O₃/SiO₂ interface, a dipole layer is formed by the migration of oxygen ions from the Al₂O₃ side to the SiO₂ side. By way of contrast, opposite dipole moments appear at the MgO/SiO₂ and SrO/SiO₂ interfaces, because of a preferential migration of metal cations from the high-k oxide toward the SiO₂ layer in the course of the formation of a stable silicate phase. These results indicate that the migrations of both oxygen ions and metal cations are responsible for the formation of the dipole layer in high-k/SiO₂ interfaces.