Valence change memories, where the change in resistance is based on the oxygen ion migration, have gained significant attention as potential candidates for both memory and neuromorphic applications. Among other perovskite-related materials, the memristive behavior of La₂NiO_4+δ (L2NO4)-based devices has been recently investigated using different electrodes and device configurations [1–4]. In the L2NO4 structure, interstitial oxygen serves as a negative charge defect, so its presence as a highly mobile ion in combination with a reactive TiN electrode leads to the creation of a TiN_xO_y interlayer at the metal/oxide interface due to the oxygen surplus in the L2NO4 films [4]. It was demonstrated that the TiN/L2NO4/Pt devices show non-volatile resistive switching (RS) with unique properties, such as a “soft-forming” step, which contrary to most filamentary devices does not require the application of a higher voltage to initialize the RS process and does not induce binary RS in the device. Thus, TiN/L2NO4/Pt devices demonstrate gradual analog RS and the ability of the conductance update under the application of the voltage pulses, i.e. long-term potentiation (LTP) and depression (LTD) when used as synaptic devices in neuromorphic systems [4]. It was also previously shown that the oxygen content in the L2NO4 film can be modified by post-deposition annealing in a wide range of oxygen stoichiometry, which can strongly influence the RS behavior [2].

In this work, the resistive switching behavior of the TiN/L2NO4/Pt devices is thoroughly investigated based on the thermally annealed L2NO4 films. We show that it is possible to control the interstitial oxygen content (δ) in the L2NO4 films by annealing using a reducing (Ar) or oxidizing (O₂) atmosphere, which allows for the tuning of the RS properties of the devices. The difference in the initial stoichiometry of the devices was confirmed by XRD and XANES analysis. We show that the annealing in the Ar atmosphere increases the initial resistance of the device, resulting in the filamentary behavior with the classical forming step. At the same time, the filamentary RS in the Ar annealed sample exhibits LTP/LTD with µs range pulses, allowing to achieve a larger memory window at the reduced energy consumption. On the contrary, thermal annealing in the O₂ atmosphere leads to the forming-free behavior with HRS and LRS resistance depending on the device area, which indicates that the interfacial type switching is dominant in the O₂ annealed device. However, the slower switching kinetics of this device leads to an increase in power consumption during the potentiation and depression of synapses. Nevertheless, both devices demonstrated the ability of LTP/LTD and STDP-based learning, which makes both devices promising candidates for neuromorphic applications for different types of architectures.