Reversal of Tunneling Electroresistance in Ferroelectric Tunnel Junctions by Interface Engineering

The tunneling electroresistance (TER) effect is a sizable change in resistance upon the reversal of ferroelectric polarization in a ferroelectric tunnel junction (FTJ), which consists of two metal electrodes separated by a nm-thick ferroelectric barrier. Usually, for TER, the resistance is expected to be low (high) when polarization points to the electrode with a longer (shorter) screening length. We show, however, that this observation is not always valid, and TER can be reversed by changing the interface termination. Using density functional theory calculations, we demonstrate that the sign of TER in a La_1-xSr_xMnO₃/BaTiO₃/Pt FTJ depends on the interface termination, either La_1-xSr_xO/TiO₂ or MnO₂/BaO. Due to the opposite sign of interfacial ionic charges, these interfaces shift the Fermi energy of La_1-xSr_xMnO₃ closer to either the conduction band minimum (La_1-xSr_xO/TiO₂) or the valence band maximum (MnO₂/BaO) of BaTiO₃ resulting in the crossover between electron and hole tunneling. Due to the opposite energy dependence of the tunneling probability, these two tunneling regimes exhibit a reversed TER.