Enhanced tunneling electroresistance in ferroelectric tunnel junctions achieved through dual interface control

Interface engineering in ferroelectric tunnel junctions is a fertile playground to realize large tunneling electroresistance (TER) ratios. Here, the TER effect of Pt/La0.8Ca0.2MnO3 (LCMO)/BaTiO3 (BTO)/Nb: SrTiO3 (NSTO) ferroelectric tunnel junctions (FTJs) is investigated. It is found that the TER is enhanced by 2 orders of magnitude for the FTJ with a 0.5 nm (similar to one unit cell) LCMO layer, as compared to its counterpart without LCMO. The observed effect is attributed to the NSTO/BTO and LCMO/BTO interfaces, both of which are responsive to ferroelectric polarization. These interfaces exhibit metallic or insulating behavior synchronously depending on the direction of the polarization in the BTO layer, resulting from the ferroelectric electric field effect and metal-insulator phase transition, respectively. This switching action with polarization reversal significantly increases the contrast in electrical resistance between the high resistance state (OFF state) and the low resistance state (ON state), therefore triggering a large TER. The increase in LCMO thickness (from 0.5 to 1 and 2 nm) leads to the decrease in TER, owing to the decreased barrier height/width at the NSTO/BTO interface, as revealed by the electron transport mechanism of Fowler-Nordheim (FN) tunneling.