Giant tunneling electroresistance in two-dimensional ferroelectric tunnel junctions with out-of-plane ferroelectric polarization

Ferroelectric tunnel junctions (FTJs) have been intensively studied in recent years due to the great potential in nonvolatile memory devices and two-dimensional (2D) FTJs have started to catch attention lately because of their atomic thickness and their significance in miniaturizing FTJ device sizes. In this work, we propose a mechanism for building 2D FTJs based on the large difference between the two work functions of a 2D ferroelectric polar material with out-of-plane polarization. When it forms a van der Waals (vdW) vertical heterostructure with another 2D material there will be two kinds of interfaces, according to which surface of the 2D polar material is contacted. Depending on the relative work functions of the contacted surfaces of the two materials, charge transfer may or may not occur between them, thus the 2D polar material may become conducting or be still insulating, resulting in two distinct conducting states (ON and OFF). We demonstrate the feasibility of this proposal by the example of a vdW heterostructure FTJ constructed with graphene and 2D ferroelectric In2Se3 with out-of-plane polarization. Specifically, based on density functional calculations, we show that excellent tunnel electroresistance (TER) effect with TER ratio similar to 1 x 10(8) % is achieved, suggesting a promising route for applying 2D ferroelectric materials with out-of-plane polarization in ferroelectric memory devices.