Reversal of Tunneling Electroresistance in Ferroelectric Tunnel Junctions by Interface Engineering

A ferroelectric tunnel junction (FTJ) consists of two metal electrodes separated by a nm-thick ferroelectric barrier which allows quantum-mechanical tunneling through it. A tunneling electroresistance (TER) effect is a sizable change in resistance of a FTJ with reversal of ferroelectric polarization. Depending on the energy alignment between electrodes and barrier, the tunneling conductance can be dominated by either electrons or holes. For electron (hole) tunneling, the Fermi energy lies closer to the conduction band minimum (valence band maximum) of the barrier. Low (high) resistance is achieved when polarization is pointing to the electrode with longer screening length for electron (hole) tunneling, referred to as positive (negative) TER. In this work, using density functional theory calculations, we demonstrate the crossover between the electron-like and hole-like tunneling in a practical FTJ La_1-xSr_xMnO₃/BaTiO₃/Pt with positive (La_1-xSr_xO)^1-x/(TiO₂)⁰ and negative (MnO₂)^x-1/(BaO)⁰ interface terminations. The positively (negatively) charged interface pulls down (up) the electrostatic potential energy at the interface and thus shifts Fermi energy of La_1-xSr_xMnO₃ closer to the conduction band minimum (valence band maximum) of BaTiO₃, leading to positive (negative) TER.