Demonstration of synaptic and resistive switching characteristics in W/TiO2/HfO2/TaN memristor crossbar array for bioinspired neuromorphic computing

Abstract

In this study, resistive random-access memory (RRAM)-based crossbar arrays with a memristor W/TiO2/HfO2/TaN structure were fabricated through atomic layer deposition (ALD) to investigate synaptic plasticity and resistive switching (RS) characteristics for bioinspired neuromorphic computing. X-ray photoelectron spectroscopy (XPS) was employed to explore oxygen vacancy concentrations in bilayer TiO2/HfO2 films. Gaussian fitting for O1s peaks confirmed that the HfO2 layer contained a larger number of oxygen vacancies than the TiO2 layer. In addition, HfO2 had lower Gibbs free energy (Delta G degrees = -1010.8 kJ/mol) than the TiO2 layer (Delta G degrees=-924.0 kJ/mol), resulting in more oxygen vacancies in the HfO2 layer. XPS results and AG degrees magnitudes confirmed that formation/disruption of oxygen-based conductive filaments took place in the TiO2 layer. The W/TiO2/HfO2/TaN memristive device exhibited excellent and repeatable RS characteristics, including superb 10(3) dc switching cycles, outstanding 10 7 pulse endurance, and high-thermal stability (10(4) s at 125 degrees C) important for digital computing systems. Furthermore, some essential biological synaptic characteristics such as potentiation-depression plasticity, paired-pulse facilitation (PPF), and spike-timing-dependent plasticity (STDP, asymmetric Hebbian and asymmetric antiHebbian) were successfully mimicked herein using the crossbar-array memristive device. Based on experimental results, a migration and diffusion of oxygen vacancy based physical model is proposed to describe the synaptic plasticity and RS mechanism. This study demonstrates that the proposed W/TiO2/HfO2/TaN memristor crossbar-array has a significant potential for applications in non-volatile memory (NVM) and bioinspired neuromorphic systems. (C) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.