Anatomy of filamentary threshold switching in amorphous niobium oxide

Abstract

The threshold switching behavior of Pt/NbO /TiN devices is investigated as a function device area and NbO film thickness and shown to reveal important insight into the structure of the self-assembled switching region. The devices exhibit combined selector-memory (1S1R) behavior after an initial voltage-controlled forming process, but exhibit symmetric threshold switching when the RESET and SET currents are kept below a critical value. In this mode, the threshold and hold voltages are independent of the device area and film thickness but the threshold current (power), while independent of device area, decreases with increasing film thickness. These results are shown to be consistent with a structure in which the threshold switching volume is confined, both laterally and vertically, to the region between the residual memory filament and the TiN electrode, and where the memory filament has a core-shell structure comprising a metallic core and a semiconducting shell. The veracity of this structure is demonstrated by comparing experimental results with the predictions of a simple circuit model, and more detailed finite element simulations. These results provide further insight into the structure and operation of NbO threshold switching devices that have application in emerging memory and neuromorphic computing fields.

Metal-oxide interface reactions and their effect on integrated resistive/threshold switching in NbO x

“…Threshold and hold voltages were extracted from the current-controlled NDR characteristics and were found to have mean values of -2.2±0.25 V and -1.6±0.3 V respectively, independent of the top electrode metals as shown in Area dependent NDR characteristics were also measured for the Nb TE devices and the threshold and hold voltages were found to be independent of device area (device dimension ranging from 5µm to 20µm). These results are consistent with earlier studies [25,27] and highlight that the electroforming process introduced a conductive filament in the Nb2O5 film and a localized threshold switching volume was self-assembled at one of the electrode/oxide interfaces [4,28,29].…”

Negative Differential Resistance Characteristics in Forming‐Free NbOx with Crystalline NbO2 Phase

“…Various transition metal oxides such as TiO x , TaO x , VO x , and NbO x were reported to show NDR. [ 6–18 ] Among these oxides, NbO x films particularly exhibit two types of NDR characteristics, namely, S‐type [ 8–16 ] and snapback, [ 15–20 ] under current‐source measurement. Recent studies suggest that the continuous S‐type NDR in amorphous NbO x films is attributed to the temperature‐dependent Poole–Frenkel (P–F) model with local Joule heating.…”

“…Recent studies suggest that the continuous S‐type NDR in amorphous NbO x films is attributed to the temperature‐dependent Poole–Frenkel (P–F) model with local Joule heating. [ 9–14 ] However, the P–F‐based model cannot explain the discontinuous snapback NDR that is manifested as abrupt voltage changes under current‐source measurement. In response, a model based on the metal–insulator transition (MIT) was proposed.…”

“…However, Li et al [ 15 ] recently proposed a material‐independent current redistribution model to explain the snapback NDR in non‐MIT materials. [ 8,23,24 ] In this study, the core–shell model [ 11 ] was applied, where a switching filament (i.e., core) with high conductivity was surrounded by a shell region with low conductivity. Moreover, the NDR was assumed to occur through the localized oxygen vacancy filament formed by the electroforming process in the amorphous NbO x film where the shell resistance acted as a parallel resistor.…”

Self-clocking fast and variation tolerant true random number generator based on a stochastic mott memristor

“…We designated them NDR-1 and NDR-2, respectively. Both NDRs are well understood as thermally-activated transport and mott transition, respectively [10][11][12][13][14][15][16] . NDR-1 is attributed to the thermally-activated transport mechanism; as the current increases, the device temperature increases by Jouleheating, and this activates the carrier injection, leading to the current increase.…”