Electroresistance of Pt/BaTiO3/LaNiO3 ferroelectric tunnel junctions and its dependence on BaTiO3 thickness

Recently, ferroelectric tunnel junctions (FTJs) have attracted considerable attention due to their great potential in next generation non-volatile memories. In this work, we report on thickness-dependent tunneling electroresistance (TER) and corresponding evolution of transport behavior in Pt/BaTiO3/LaNiO3 FTJs with various BaTiO3 thicknesses of 2.0, 3.2, and 4.8 nm. The TER effect is observed in the 3.2 nm-thick Pt/BaTiO3/LaNiO3 tunnel junction and an ON/OFF current ratio of ∼170 is achieved due to the modulation of barrier height by polarization reversal. When the BaTiO3 is increased to 4.8 nm in thickness, the ferroelectric-modulation of the barrier profile becomes more pronounced and the dominant transport mechanism changes from electron tunneling to thermally-activated thermionic injection. As a result, the OFF state current is significantly reduced due to the suppression of the Fowler-Nordheim tunneling with increased width and height of the BaTiO3 barrier. A greatly improved ON/OFF current ratio of ∼12 500 is thus achieved in the 4.8 nm-thick Pt/BaTiO3/LaNiO3 FTJ device. These results facilitate deeper understanding of the TER effects from the viewpoint of not only the barrier profile but also the transport mechanism.