Resistive switching in tunnel junctions with a single-crystal La2NiO4 electrode

We study the resistive switching in tunnel junctions with single-crystal La2NiO4 electrodes. Such electro-resistive devices are promising candidates for future nonvolatile memory and reconfigurable logic applications thanks to their simple structure, excellent scalability and endurance. Our tunnel junctions were prepared by painting a spot of conductive silver epoxy on the surface of a La2NiO4 single crystal. The interface between the silver and the semiconducting crystal served as a natural barrier forming planar normal metal/insulator/semiconductor (N-I-S) tunnel junctions with resistances ranging from a few Ohms to more than hundred thousands of Ohms. The current-voltage (I-V) measurements performed on such junctions at room temperature demonstrated a bias-driven switching between high and low resistance states with ratios close to 100% and high endurance. A combination of 2- and 3-probe I-V measurements unambiguously demonstrated that the resistive switching is associated with the interfaces between the La2NiO4 crystal and the silver-contact electrodes, with negligible contribution from the bulk of the crystal. Similar resistive-switching phenomena in other oxide materials were previously associated with crystal-lattice distortions produced by an applied voltage/electric field. Here, we use an ultra-sensitive capacitive displacement meter to monitor the field-induced lattice distortions in situ. We observe that the crystal contraction/expansion is strongly correlated with the resistive switching. We also note that the Joule heating from dc bias may contribute to the crystal size changes. Our results provide a new insight into the origin of lattice distortions/resistive switching in transition metal oxides while the observed interfacial nature of the switching phenomenon is promising for fabrication of thin-film planar devices to be used in nonvolatile memory and logic.