Tuning resistive switching properties of WO3− x -memristors by oxygen vacancy engineering for neuromorphic and memory storage applications

Abstract

High density memory storage capacity, in-memory computation and neuromorphic computing utilizing memristors are expected to solve the limitation of von-Neumann computing architecture. Controlling oxygen vacancy (V O) defects in metal oxide thin film based memristors holds the potential of designing resistive switching (RS) properties for memory storage and neuromorphic applications. Herein, we report on RS characteristics of complementary metal–oxide–semiconductor compatible WO3−x based memristors modulated by precisely controlled oxygen non-stoichiometry. Switchability of the resistance states has been found to depend strongly on the V Os concentration in the WO3−x layer. Depending on x, the memristors exhibited forming-free bipolar, forming-required bipolar, and non-formable characteristics. Devices with moderate V Os concentration (∼5.8 × 1020 cm−3) exhibited a large R off/R on ratio of ∼6500, and reset voltage-controlled multi-level resistance states. A forming-free, stable multi-level RS has been realized for a memristor possessing V Os concentration of ∼6.2 × 1020 cm−3. WO3−x -based memristors with higher V Os concentrations (∼8.9 × 1020 cm−3–1 × 1021 cm−3) exhibited lower initial resistance, low R off/R on ratios (∼15–63) and forming-free synaptic functions with reasonable conduction modulation linearity. Investigation of the conduction mechanism suggests that tailoring V Os concentration modifies the formation and dimension of the conducting filaments and the Schottky barrier height at the WO3−x /Pt interface, which paves the way for designing WO3−x -based memristors for memory storage and neuromorphic applications.