Nanoscale Topotactic Phase Transformation in SrFeOx Epitaxial Thin Films for High‐Density Resistive Switching Memory

• Published in: Advanced materials (Weinheim) Vol. 31; no. 49; pp. e1903679 - n/a
• Main Authors: Tian, Junjiang, Wu, Haijun, Fan, Zhen, Zhang, Yang, Pennycook, Stephen J., Zheng, Dongfeng, Tan, Zhengwei, Guo, Haizhong, Yu, Pu, Lu, Xubing, Zhou, Guofu, Gao, Xingsen, Liu, Jun‐Ming
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.12.2019
• Subjects: Brownmillerite; Calcium aluminum ferrite; Density; Endurance; Materials science; Materials selection; nanofilaments; Nanotechnology devices; Perovskites; Phase transitions; resistive switching; SrFeOx; Switching; Thin films; topotactic phase transformation; Transition metal oxides
• ISSN: 0935-9648; 1521-4095; 1521-4095
• DOI: 10.1002/adma.201903679

Resistive switching (RS) memory has stayed at the forefront of next‐generation nonvolatile memory technologies. Recently, a novel class of transition metal oxides (TMOs), which exhibit reversible topotactic phase transformation between insulating brownmillerite (BM) phase and conducting perovskite (PV) phase, has emerged as promising candidate materials for RS memories. Nevertheless, the microscopic mechanism of RS in these TMOs is still unclear. Furthermore, RS devices with simultaneously high density and superior memory performance are yet to be reported. Here, using SrFeOx as a model system, it is directly observed that PV SrFeO3 nanofilaments are formed and extend almost through the BM SrFeO2.5 matrix in the ON state and are ruptured in the OFF state, unambiguously revealing a filamentary RS mechanism. The nanofilaments are ≈10 nm in diameter, enabling to downscale Au/SrFeOx/SrRuO3 RS devices to the 100 nm range for the first time. These nanodevices exhibit good performance including ON/OFF ratio as high as ≈104, retention time over 105 s, and endurance up to 107 cycles. This study significantly advances the understanding of the RS mechanism in TMOs exhibiting topotactic phase transformation, and it also demonstrates the potential of these materials for use in high‐density RS memories. The resistive‐switching (RS) mechanism in SrFeOx epitaxial thin films is revealed to be the formation/rupture of perovskite SrFeO3 nanofilaments in the brownmillerite SrFeO2.5 matrix, mediated by the electric‐field‐induced local topotactic phase transformation. With this mechanism, SrFeOx‐based RS devices can be downscaled to the 100 nm range and exhibit excellent performance.