Reset-First and Multibit-Level Resistive-Switching Behavior of Lanthanum Nickel Oxide (LaNiO_3-x) Thin Films

The resistive random-access memory (RRAM) with multi-level storage capability has been considered one of the most promising emerging devices to mimic synaptic behavior and accelerate analog computations. In this study, we investigated the reset-first bipolar resistive switching (RS) and multi-level characteristics of a LaNiO_3-x thin film deposited using a reactive magnetron co-sputtering method. Polycrystalline phases of LaNiO₃ (LNO), without La₂O₃ and NiO phases, were observed at similar fractions of Ni and La at a constant partial pressure of oxygen. The relative chemical proportions of Ni³⁺ and Ni²⁺ ions in LaNiO_3-x indicated that it was an oxygen-deficient LaNiO_3-x thin film, exhibiting RS behavior, compared to LNO without Ni²⁺ ions. The TiN/LaNiO_3-x/Pt devices exhibited gradual resistance changes under various DC/AC voltage sweeps and consecutive pulse modes. The nonlinearity values of the conductance, measured via constant-pulse programming, were 0.15 for potentiation and 0.35 for depression, indicating the potential of the as-fabricated devices as analog computing devices. The LaNiO_3-x-based device could reach multi-level states without an electroforming step and is a promising candidate for state-of-the-art RS memory and synaptic devices for neuromorphic computing.