Evidence of Biorealistic Synaptic Behavior in Diffusive Li-based Two-terminal Resistive Switching Devices

Following the recent advances in artificial synaptic devices and the renewed interest regarding artificial intelligence and neuromorphic computing, a new two-terminal resistive switching device, based on mobile Li⁺ ions is hereby explored. Emulation of neural functionalities in a biorealistic manner has been recently implemented through the use of synaptic devices with diffusive dynamics. Mimicking of the spontaneous synaptic weight relaxation of neuron cells, which is regulated by the concentration kinetics of positively charged ions like Ca²⁺, is facilitated through the conductance relaxation of such diffusive devices. Adopting a battery-like architecture, using LiCoO₂ as a resistive switching cathode layer, SiO_x as an electrolyte and TiO₂ as an anode, Au/LiCoO₂/SiO_x/TiO₂/p⁺⁺-Si two-terminal devices have been fabricated. Analog conductance modulation, via voltage-driven regulation of Li⁺ ion concentration in the cathode and anode layers, along with current rectification and nanobattery effects are reported. Furthermore, evidence is provided for biorealistic synaptic behavior, manifested as paired pulse facilitation based on the summation of excitatory post-synaptic currents and spike-timing-dependent plasticity, which are governed by the Li⁺ ion concentration and its relaxation dynamics.