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

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 V_o based conducting filament in a-Ta₂O₅. Iso-surface charge density plots confirmed the formation of intrinsic V_o based conducting filaments in a-Ta₂O₅. These conducting filaments became stronger with increasing concentration of V_os in a-Ta₂O₅. Integrated charge density, density of states (DOS), and potential line ups also confirmed that V_o 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 (V_o).