Resistive switching characteristics and theoretical simulation of a Pt/a-Ta2O5/TiN synaptic device for neuromorphic applications

Abstract

Internet of things and big data demand the development of new techniques for memory devices going beyond conventional ways of memorizing and computing. In this work, we fabricated a Pt/a-Ta2O5/TiN resistive switching memory device and demonstrated its resistive and synaptic characteristics. Firstly, X-ray photoelectron spectroscopy (XPS) of a-Ta2O5/TiN analysis was conducted to determine elemental compositions of a-Ta2O5/TiN and TiON interfacial layer between a-Ta2O5 and TiN layer. Repetitive bipolar resistive switching was achieved by a set at a negative bias and a reset at a positive bias. Moreover, its biological potentiation and depression behaviors were well emulated by applying a repetitive pulse on the device. For deep understanding of this device’s properties based on materials, oxygen vacancies, and stack engineering, theoretical calculations were performed employing Vienna ab-initio simulation Package (VASP) code. All calculations were carried out using PBE and GGA+U method to obtain accurate results. Work function difference between electrodes provided a localized path for forming a Vo based conducting filament in a-Ta2O5. Iso-surface charge density plots confirmed the formation of intrinsic Vo based conducting filaments in a-Ta2O5. These conducting filaments became stronger with increasing concentration of Vos in a-Ta2O5. Integrated charge density, density of states (DOS), and potential line ups also confirmed that Vo was responsible for charge transportation in a-Ta2O5 based RRAM devices. Experimental and theoretical results confirmed the formation of TiON layer between a-Ta2O5 and active electrode (TiN), suggesting that the bipolar resistive switching phenomenon of the proposed device was based on oxygen vacancy (Vo).