Threshold Switching and Conductance Quantization in Al/HfO₂/Si(p) Structures

Abstract

Volatile threshold switching and non-volatile memory switching modes of resistive switching are reported in Al/HfO2/Si(p) metal–oxide–semiconductor structures with different values of current compliance limit during electroforming. When the current is limited to below 100 µA, a reproducible threshold switching loop is reported under injection from the p-type silicon substrate. The conduction in the low resistance state is linear above a voltage threshold called holding voltage and the conductance is a non-integer multiple of the quantum of conductance. Depending on the size of the conducting filament created during the electroforming process, one or several quasi-one dimensional quantum subbands are found to contribute to the current. Abrupt transitions between different discrete conductance values are reported during increasing and decreasing voltage sweeps. These results provide strong experimental evidence suggesting that the conduction filament behaves as a quantum wire (QW). No structural instability of the filament has to be invoked to explain either the highly structured conduction properties or the set and reset switching transitions. It is claimed that the whole phenomenology can be understood by electron injection from the valence band into a narrow conducting path which behaves as a QW.

Resistive Switching Performance Improvement via Modulating Nanoscale Conductive Filament, Involving the Application of Two‐Dimensional Layered Materials

“…Since the thinnest part of CF is only composed of several atoms, the diffusion of single atom will have a significant impact on the whole conductance, and the variation is not continuous any more, but is integer or half integer multiples of quantum conductance (Figure f). In fact, in ECM, VCM, TCM, and even TS devices, quantum conductance has all been observed.…”

“…Apart from the above three non‐volatile memory switching mechanisms, there is a volatile threshold switching (TS) effect (Figure e,j,o). Different from the conventional non‐volatile RS, LRS in the TS cycle can be returned back to HRS with applied voltage below a certain value (Figure c) . The TS mechanism can be illustrated with the following example ( Figure ).…”

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

“…Generally, RS behavior can be classified as two modes: nonvolatile memory switching (MS) and volatile threshold switching (TS). In the MS mode, both LRS and HRS can be maintained after removing the external voltage, while the LRS in the TS mode will be back to the HRS once the applied voltage is smaller than a critical value . To avoid confusion with MS, the LRS and HRS in TS are renamed as “TS ON‐state” and “TS OFF‐state” in this article.…”

“…The MS device can be used for the non‐volatile data storage while TS device can be as a selector in series with memory cell to suppress crosstalk effect in the crossbar array . Recently, some groups reported that TS and MS can coexist and mutually transform in a single device at suitable external excitation . Several models have been proposed to explain this phenomenon, including CF thermal instability, strong electron correlation effect, quantum‐wire model, interface barrier modulation, and space charge effect .…”

“…Recently, some groups reported that TS and MS can coexist and mutually transform in a single device at suitable external excitation . Several models have been proposed to explain this phenomenon, including CF thermal instability, strong electron correlation effect, quantum‐wire model, interface barrier modulation, and space charge effect . However, the underlying mechanism of the phenomenon is still unclear, especially lacking of direct evidences to uncover when and how the two RS modes happen and what is the internal relationship between them.…”