In-depth analysis of core-shell filaments in nonvolatile NbOx memristive device as an artificial synapse for multifunctional bionic applications

As a key building block of the biological cortex, synapses are powerful information processing units that enable highly complex nonlinear computations. The realization of artificial synapses with similar capabilities has important implications for building intelligent, neuromorphic systems. Here, we demonstrate an artificial synapse based on NbOx nonvolatile memristor to mimic multifunctional bionic applications such as nociceptor and associative learning. Combined experimental characterization with COMSOL simulation, the traditional resistance switching characteristics, which are the decisive factor for the synapse properties are in-depth analyzed. It can be proposed that the I–V characteristics of Pt/NbOx/TiN memristor are governed by core-shell filaments consisting of the shell region of sub-stoichiometric Nb2O5−δ and the core of NbO2. On the basis of the core-shell filament model, it can be reasonably explained that Ohmic conduction and Poole-Frenkel conduction take turns to dominate the current flowing in the memristive device, leading to the zigzag evolution of current during the operation process of NbOx-based device. The simulations of synaptic plasticity, including long-term potentiation/depression (LTP/LTD), paired-pulse facilitation (PPF), and spike-timing-dependent plasticity (STDP), exhibiting that the NbOx can be utilized for an artificial synapse. Furthermore, bionic functions such as hyperalgesia and allodynia of a nociceptor and a series of associative learning behaviors in Pavlovian dog experiment are mimicked, illustrating that the Pt/NbOx/TiN have great potential for highly simplified artificial neural network applications.