Unraveling the Origin and Mechanism of Nanofilament Formation in Polycrystalline SrTiO3 Resistive Switching Memories

• Published in: Advanced materials (Weinheim) Vol. 31; no. 28; pp. e1901322 - n/a
• Main Authors: Kwon, Deok‐Hwang, Lee, Shinbuhm, Kang, Chan Soon, Choi, Yong Seok, Kang, Sung Jin, Cho, Hae Lim, Sohn, Woonbae, Jo, Janghyun, Lee, Seung‐Yong, Oh, Kyu Hwan, Noh, Tae Won, De Souza, Roger A., Martin, Manfred, Kim, Miyoung
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-07-2019
• Subjects: Deduction; Electrical measurement; Electrode polarization; Electrodes; Energy transmission; Filaments; Grain boundaries; memristors; nanofilaments; Phase diagrams; Polycrystals; resistive switching; Strontium titanates; Switching; Thin films; Transmission electron microscopy; transmission electron microscopy (TEM)
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201901322

Three central themes in the study of the phenomenon of resistive switching are the nature of the conducting phase, why it forms, and how it forms. In this study, the answers to all three questions are provided by performing switching experiments in situ in a transmission electron microscope on thin films of the model system polycrystalline SrTiO3. On the basis of high‐resolution transmission electron microscopy, electron‐energy‐loss spectroscopy and in situ current–voltage measurements, the conducting phase is identified to be SrTi11O20. This phase is only observed at specific grain boundaries, and a Ruddlesden–Popper phase, Sr3Ti2O7, is typically observed adjacent to the conducting phase. These results allow not only the proposal that filament formation in this system has a thermodynamic origin—it is driven by electrochemical polarization and the local oxygen activity in the film decreasing below a critical value—but also the deduction of a phase diagram for strongly reduced SrTiO3. Furthermore, why many conducting filaments are nucleated at one electrode but only one filament wins the race to the opposite electrode is also explained. The work thus provides detailed insights into the origin and mechanisms of filament generation and rupture.
Formation and rupture of nanofilaments are directly observed by in situ current–voltage/transmission electron microscopy to investigate the resistive‐switching mechanism in a model oxide system of polycrystalline SrTiO3 thin film. High‐resolution transmission electron microscopy, electron‐energy‐loss spectroscopy, and in situ current–voltage measurements reveal the filament‐phase SrTi11O20 and its neighboring structure, which fundamentally establishes the thermodynamic origin and mechanism.