Electric Field- and Current-Induced Electroforming Modes in NbO_x

Abstract

Electroforming is used to initiate the memristive response in metal/oxide/metal devices by creating a filamentary conduction path in the oxide film. Here, we use a simple photoresist-based detection technique to map the spatial distribution of conductive filaments formed in Nb/NbO x /Pt devices, and correlate these with current–voltage characteristics and in situ thermoreflectance measurements to identify distinct modes of electroforming in low- and high-conductivity NbO x films. In low-conductivity films, the filaments are randomly distributed within the oxide film, consistent with a field-induced weakest-link mechanism, while in high-conductivity films they are concentrated in the center of the film. In the latter case, the current–voltage characteristics and in situ thermoreflectance imaging show that electroforming is associated with current bifurcation into regions of low and high current density. This is supported by finite element modeling of the current distribution and shown to be consistent with predictions of a simple core–shell model of the current distribution. These results clearly demonstrate two distinct modes of electroforming in the same material system and show that the dominant mode depends on the conductivity of the film, with field-induced electroforming dominant in low-conductivity films and current bifurcation-induced electroforming dominant in high-conductivity films.

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

“…It is still controversial whether the electroforming process could create a crystalline NbO 2 phase region [ 30–32 ] or filaments of high‐current‐density oxygen vacancies. [ 33 ] Consequently, the nature of the conduction paths would affect the NDR characateristics of amorphous NbO x . In the previous work, amorphous NbO x devices with an electroforming process were used for the NDR study.…”

Electric Field‐Induced Area Scalability toward the Multilevel Resistive Switching

“…In fact, recently, a better control over the device switching performance with high uniformity (device to device) and reproducibility (cycle to cycle) have been realized by controlling the oxygen vacancies along the vertical interface by the confinement of the CF. [8,14,27] Therefore, if the nanoscale conducting paths can be confined within well-defined region and shape using an external electric field, oxygen vacancies within the conductive path can be controlled for each switching operation. [7,8,28] As a result, the improved uniformity and reproducibility in RS can be obtained towards multilevel switching and neuromorphic computing; this is obviously considered as a breakthrough.…”

“…[8,14,27] Therefore, if the nanoscale conducting paths can be confined within well-defined region and shape using an external electric field, oxygen vacancies within the conductive path can be controlled for each switching operation. [7,8,28] As a result, the improved uniformity and reproducibility in RS can be obtained towards multilevel switching and neuromorphic computing; this is obviously considered as a breakthrough.…”

“…Indeed, in multilevel RS device, the current or resistance across the device can be modulated to different levels in response to the applied electric field, resulting the formation and rupture of the conducting filament (CF). [7][8][9][10][11] In many metal oxide RRAM devices, the formation and rupture of CF had been clarified based on the migration and redistribution of applied electric field-assisted localized defects such as oxygen vacancies. [12][13][14] Nevertheless, a better control of oxygen ion or vacancy generation rates and their distribution dynamics with the time or applied electric field still remain unclear.…”

Memristive Behaviors Dominated by Reversible Nucleation Dynamics of Phase‐Change Nanoclusters

“…This considerably differs in terms of both preparing and measuring the NbO 2 Mott transition materials. [27] Such a reversible disorder-order transition, or local structure fluctuation allows the system to modulate the input signal adaptively.…”