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

Abstract

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.