Giant Tunneling Electroresistance Induced by Interfacial Doping in Pt/BaTiO3/Pt Ferroelectric Tunnel Junctions

Abstract

Ferroelectric tunnel junctions (FTJs) are very promising candidates for nonvolatile memory devices and a large tunneling electroresistance (TER) ratio is essential for their high performance. This work intends to achieve large TER ratio by interfacial doping in FTJs by taking ${\mathrm{Pt}/\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_{3}/\mathrm{Pt}$ tunnel junctions as an example. By introducing Na (or $\mathrm{Li}$) substitutions for $\mathrm{Ti}$ atoms at the right interface, the resultant strong Coulomb repulsion from the negatively charged ${\mathrm{Na}\mathrm{O}}_{2}$ interface pushes the electrons to higher energy in an increasing manner from left to right in the whole ${\mathrm{Ba}\mathrm{Ti}\mathrm{O}}_{3}$ barrier, which leads to rapidly increasing potential energy profile and partial metallization close to the right interface in the left polarization state. However, in the right polarization state, since the right ferroelectric polarization produces a decreasing potential energy profile from left to right, although the ${\mathrm{Na}\mathrm{O}}_{2}$ interface also pushes the electrons to much higher energy and the slope of the potential energy profile changes from negative to positive, the final slope of the potential energy profile is much less steeper and the Fermi level is always inside the band gap, leading to a completely insulating state. The substantially different distributions of the electrostatic potential energy profile in the two polarization states lead to great differences in the transport properties. Based on density-functional-theory calculations, a TER ratio up to ${10}^{5}$% is achieved. The results indicate that a negatively charged interface based on interfacial substitution is a promising method for obtaining a large TER ratio in FTJs, and thus will have implications for the further understanding and design of high-performance FTJs.