Giant tunneling electroresistance induced by ferroelectric-antiferroelectric transition in two-dimensional ultrathin perovskite ferroelectric tunnel junctions

The stripping of two-dimensional (2D) perovskite thin films with thickness of only several atomic layers from 3D perovskite materials has been reported experimentally recently, which makes it possible to fabricate 2D perovskite ferroelectric tunnel junctions (FTJs). Motivated by this and based on density functional calculations, we design the 2D ${\mathrm{SrRuO}}_{3}/{\mathrm{BaTiO}}_{3}/{\mathrm{LaAlO}}_{3}/{\mathrm{SrRuO}}_{3}$ FTJ as a prototype to explore the performance of 2D perovskite FTJs relative to the 3D counterpart. The bistable states of the 2D FTJ are obtained as ferroelectric and antiferroelectric (AFE) states, which are different from those of the traditional 3D-perovskite FTJs, which usually have only uniform left polarization state and right polarization state. Importantly, first-principles calculations demonstrate that the switching between these two states results in the TER ratio as high as $4.570\ifmmode\times\else\texttimes\fi{}{10}^{5}%$, which is nearly two orders of magnitude larger than that ($9.656\ifmmode\times\else\texttimes\fi{}{10}^{3}%$) of the 3D counterpart. Further analysis indicates that it arises from the unusual higher transmission due to the interlayer resonant tunneling between the top and bottom layers in the antiferroelectric state in the 2D case as compared with the uniform polarization states. Consequently, when the perovskite FTJs are thinned down to the thickness of only several atomic layers, new states (AFE state in this device) may appear and thus strengthen the TER performance, providing new routes for designing perovskite-type FTJs and decreasing the device sizes.