Excellent synaptic behavior of lithium-based nano-ionic transistor based on optimal WO _2.7 stoichiometry with high ion diffusivity

Abstract

In this study, we introduce a lithium (Li) ion-based three-terminal (3-T) synapse device using WO _x as a channel. Our study reveals a key stoichiometry of WO_2.7 for excellent synaptic characteristics that is related to Li-ion diffusivity. The open-lattice structure formed by oxygen deficiency promoted Li-ion injection and diffusion. The optimized stoichiometry and improved Li-ion diffusivity were confirmed by x-ray photoelectron spectroscopy analysis and cyclic voltammetry, respectively. Furthermore, the transient conductance change that inevitably occurs in ion-based synaptic transistors was resolved by applying a two-step voltage pulse scheme. As a result, we achieved a symmetric and linear weight-update characteristic with reduced program/erase operation time.