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

Abstract

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.

A Review of Resistive Switching Devices: Performance Improvement, Characterization, and Applications

“…[ 49,168,169 ] Figure 8e shows HRTEM images of a SrTiO 3 ‐based RS device after in situ forming and RESET operation. [ 170 ] It is observed that a SrTi 11 O 20 filament and the Ruddlesden–Popper (RP) phase are formed during the forming process. However, during the RESET, the filament is partially or completely ruptured, depending on the magnitude of the applied current, and the RP phase disappears.…”

Inhomogeneity and Segregation Effect in the Surface Layer of Fe-Doped SrTiO3 Single Crystals

“…Nevertheless since the change of resistance in such materials is non-volatile and reversible, they are treated as prospective candidates for the development of non-volatile memory devices, next-generation logic devices and neuromorphic systems [2][3][4][5]. Among various materials remarkable advancements have been observed in the field of transition metal oxides [6][7][8]. SrTiO 3 (STO) [9], between other ternary (or binary like TiO 2 [10]) transition metal oxides, may be especially suited for memory applications [11].…”

Coupled Morphological Stability of the Multiple Phase Boundaries: Oxides in an Oxygen Potential Gradient. II. Two Oxide Layers

“…Recently, very thin oxide films, e.g. SrTiO 3 or GaO x have found increased interest due to their ability for resistive switching [8,9]. In all of these examples, oxygen potential gradients appear across the oxide layer, either directly applied externally or as a result of another applied gradient.…”