Sanghyo Lee1,Hyoung Gyun Kim1,Ventaka Nallagatla2,Chang Uk Jung2,Deok-Hwang Kwon3,Miyoung Kim1
Seoul National University1,Hankuk University of Foreign Studies2,Korea Institute of Science and Technology3
Sanghyo Lee1,Hyoung Gyun Kim1,Ventaka Nallagatla2,Chang Uk Jung2,Deok-Hwang Kwon3,Miyoung Kim1
Seoul National University1,Hankuk University of Foreign Studies2,Korea Institute of Science and Technology3
Redox-based memristive devices are one of the most attractive candidates as a synapse for neuromorphic computing system due to its non-volatility and high operating speed. It is necessary to analyze the behavior of oxygen ions to better understand the resistive switching mechanism. Previously, we discovered the resistive switching behavior through topotactic phase transition of SrFeO<sub>x</sub> through Au/SrFeO<sub>x</sub>/SrRuO<sub>3</sub> device. Here, we studied Au/SrFeO<sub>x</sub>/Nb: SrTiO<sub>3</sub> device grown epitaxially in (111) direction to understand the migration of oxygen ions during resistive switching compared to Au/SrFeO<sub>x</sub>/SrRuO<sub>3</sub> device. This Au/SrFeO<sub>x</sub>/Nb: SrTiO<sub>3</sub> device has a Schottky-like I-V curve, and shows a difference in resistance of about 100 to 1000 times. In order to precisely study the mechanism of resistance change, in-situ I-V transmission electron microscopy (TEM) was used. In-situ TEM enables to observe changes in atomic structure under different resistance states by applying external field to the specimen in a TEM. Moreover, oxygen ionic migration as well as oxidation states of transition metals can be measured simultaneously by electron energy loss spectroscopy.<br/>In the pristine state, the SrFeO<sub>x</sub> layer mainly exists as a perovskite structure. However, after the forming process, a phase change occurred to the brownmillerite structure near the interface with bottom electrode Nb: SrTiO<sub>3</sub>. The structure during SET and RESET cycles did not change significantly, and only the area of perovskite in HRS was partially reduced. Unlike the previous work, the main factor of the resistance change comes from the Nb: SrTiO<sub>3</sub> interface close to SrFeO<sub>x</sub> layer not from SrFeO<sub>x</sub> layer itself. When a positive bias is applied to the top electrode, oxygen vacancies are accumulated near the Nb: SrTiO<sub>3</sub> interface under the brownmillerite SrFeO<sub>2.5</sub> and the resistance value is lowered. Conversely, as a negative bias is applied to the top electrode, oxygen ions piles up at the interface and the device’s resistance increases. In this system, the SrFeO<sub>x</sub> layer acts as an oxygen reservoir and transport path, and it can alter the oxygen ions concentration on the Nb: SrTiO<sub>3</sub> surface easily. This study provides a better understanding and applicability of perovskite-based memristive devices.