Enhanced bio-synaptic plasticity behaviour through controlled defect migration in nano-columnar WO3−x memristors

Abstract

Two-terminal memristors have attracted significant research attention owing to their promising applications in non-volatile memory and brain-inspired neuromorphic computing systems. However, attaining reliable memristive and neuromorphic functionalities at nanoscale is essential for developing high-density, low-power devices designed for intensive data processing, posing a considerable challenge. In this report, we present a simple yet effective approach to attain superior bio-synaptic functionalities in tungsten trioxide (WO_3−x)-based memristors at nanoscale by restricting the oxygen vacancy (V_O) migration through compact nano-columnar structures developed using glancing angle deposition method. The restricted ionic migration is feasible owing to different V_O concentrations inside the nano-columns and their boundaries, as inferred by nanoscale scanning probe microscopic techniques. The nanostructured-WO_3−x memristors exhibit improved and reliable synaptic plasticity behaviours in comparison to their thin film-based counterparts when exposed to different pulse stimulations. Furthermore, the nanostructured devices demonstrate “experience-dependent plasticity,” where the synaptic plasticity is significantly influenced by the frequency of preceding pulses. In contrast, uncontrolled filament growth/destruction leads to a poor synaptic display in thin film-based WO_3−x memristors. Moreover, various spectroscopic and electrical studies support the proposed physical mechanisms. Therefore, the present study paves the way to accomplish reliable synaptic functionalities at nanoscale for next-generation highly efficient neuromorphic systems.