Ferroelectric tunneling through a composite barrier under bias voltages

Abstract

Here we demonstrate theoretical investigations of tunneling in ferroelectric tunnel junctions (FTJs) with a composite barrier. The results show that the SrRuO3/SrTiO3/BaTiO3/SrRuO3 composite FTJ has a larger tunneling electroresistance (TER) effect than the SrRuO3/SrTiO3/BaTiO3/Pt composite FTJ. The TER in the SrRuO3/SrTiO3/BaTiO3/SrRuO3 FTJ is 11700% at +0.05 V and increase to 25400% at +0.3 V, 5 ∼ 7 times higher than the corresponding TER value of the SrRuO3/SrTiO3/BaTiO3/Pt FTJ. The enhanced TER is ascribed to the enlarged asymmetric factor. For SrRuO3/SrTiO3/BaTiO3/Ti FTJs in which the total barrier thickness is fixed to 10 unit cells, it is found that the SrTiO3(4 unit cells)/BaTiO3(6 unit cells) composite barrier can yield the largest TER value, well consistent with the experimental results. The optimal thickness for the maximum TER can also be explained by the dependency of the asymmetric factor on the TER, considering the difference in the average barrier height of the FTJs for two opposite polarization orientations changes with the thickness distribution and it could be the largest for the optimal structure.