Low-Temperature Tunneling Electroresistance in Ferromagnetic Metal/Ferroelectric/Semiconductor Tunnel Junctions.

Abstract

Ferroelectric tunnel junctions (FTJs) as artificial synaptic devices are promising candidates for the building block of nonvolatile data storage devices. However, a small ON/OFF ratio of FTJs limits their application in low-temperature operations. In this work, the influence of quantum interference effects on tunneling electroresistance in the La0.7Sr0.3MnO3/BaTiO3/Nb:SrTiO3 (ferromagnetic metal/ferroelectric/semiconductor) FTJ at low temperatures is investigated. The Current-voltage curves are observed in the tunnel junction from 300 to 10 K with a six-unit-cell thick BaTiO3 film by the ferroelectric polarization effect. First, the ON/OFF current ratio increases from 300 to 30 K due to the increase of polarization in the ferroelectric barrier, and then, it gradually decreases when the temperature drops below 30 K. An anomalous ON/OFF current ratio of ∼105 is obtained at 30 K. The low-temperature tunneling properties in the FTJ are associated with a low-temperature resistivity minimum in the ferromagnetic metal layer by the electron-electron interaction, which increases the La0.7Sr0.3MnO3/BaTiO3 interface resistance, leading to a higher resistance state and lower IOFF for the OFF state. As a result, the ON/OFF current ratio is abruptly enhanced at 30 K. Our results emphasize the crucial role of transport properties of La0.7Sr0.3MnO3 in FTJs and pave the way for the design and application of FTJs at low temperatures.