Direct Observation of Conversion Between Threshold Switching and Memory Switching Induced by Conductive Filament Morphology

• Published in: Advanced functional materials Vol. 24; no. 36; pp. 5679 - 5686
• Main Authors: Sun, Haitao, Liu, Qi, Li, Congfei, Long, Shibing, Lv, Hangbing, Bi, Chong, Huo, Zongliang, Li, Ling, Liu, Ming
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 01.09.2014
• Subjects: conductive filaments; Devices; Filaments; memory switching; Morphology; Nanocrystals; resistive random access memory (RRAM); Scanning electron microscopy; Silver; Switching; threshold switching; Thresholds
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201401304

Volatile threshold switching (TS) and non‐volatile memory switching (MS) are two typical resistive switching (RS) phenomena in oxides, which could form the basis for memory, analog circuits, and neuromorphic applications. Interestingly, TS and MS can be coexistent and converted in a single device under the suitable external excitation. However, the origin of the transition from TS to MS is still unclear due to the lack of direct experimental evidence. Here, conversion between TS and MS induced by conductive filament (CF) morphology in Ag/SiO2/Pt device is directly observed using scanning electron microscopy and high‐resolution transmission electron microscopy. The MS mechanism is related to the formation and dissolution of CF consisting of continuous Ag nanocrystals. The TS originates from discontinuous CF with isolated Ag nanocrystals. The results of current–voltage fitting and Kelvin probe force microscopy further indicate that the TS mechanism is related to the modulation of the tunneling barrier between Ag nanocrystals in CF. This work provides clearly experimental evidence to deepen understanding of the mechanism for RS in oxide‐electrolyte‐based resistive switching memory, contributing to better control of the two RS behaviors to establish high‐performance emerging devices. The coexistence of volatile threshold and non‐volatile memory switching phenomena is observed in oxide‐electrolyte‐based resistive random access memory (RRAM). The switching behaviors of the device transform from threshold to memory switching when increasing the compliance current in electroforming. Analysis reveals that the threshold and memory switching behaviors correspond to the conductive filament consisting of isolated Ag nanocrystals and continuous Ag nanocrystals, respectively.