Multiple slopes in the negative differential resistance region of NbO_x-based threshold switches

Abstract

Niobium oxide devices exhibit threshold switching behavior which enables their use as selectors in memory arrays or as locally active devices for neuromorphic computing. Among the basic dynamical phenomena appearing in non-linear circuits, the oscillations generated in a relaxation oscillator, which is making use of the negative differential resistance (NDR) effect of a threshold switching device, are of special significance for the design of neuromorphic electronic systems. Here, the necessary requirements for the emergence of oscillations of this kind in a simple relaxation oscillator circuit and their influence on the shape of the measured quasi-static I– characteristic of the threshold switch are examined. In the corresponding experiments multiple NDR regions were found to appear in the quasi-static I– characteristic of the threshold switch concurrently with the occurrence of oscillations. The observed ‘multiple NDR phenomenon’ is therefore merely a measurement artefact due to the averaging effect associated to the operating principles of the source measure unit (SMU) utilized to measure the device current and voltage. In this work, we analyzed how the emergence of oscillatory behavior in the relaxation oscillator depends upon the device layer stack composition. The probability of the appearance of oscillations within a large current range can be increased by decreasing the oxygen content in the sub-stoichiometric bottom layer of a niobium oxide bi-layer stack. It is shown that this trend is caused by the resulting decrease in the value of the product between thermal capacitance and thermal resistance of the threshold switching device. Furthermore, the changed stack composition reduces the variability and changes the forming voltage, which goes hand in hand with a change of the threshold voltage.

Direct Observation of the Electrically Triggered Insulator-Metal Transition in V3O5 Far below the Transition Temperature

“…As long as the RC time constant is larger than the thermal time constant, the oscillation regime persists. 23 In our simulations, the temperature lag is about 20 times shorter than the oscillation period, therefore the oscillation frequency could be increased substantially by controlling the interplay between the electrical and thermal inertias.…”

“…On the other hand, in V2O3 (and also radiation damaged VO2), resistive switching can be accomplished by destabilization of the Mott state by charge injection. 3 In NbO2, Joule heating has been claimed to the cause of both, local heating across the IMT 18,19 and "thermal runaway" [20][21][22][23] in the observation of resistive switching well below the Tc. This variety of possibilities illustrates that observation of resistive switching in a IMT material does not automatically indicate the triggering mechanism.…”

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

“…Electric devices that exhibit a negative differential resistance (NDR) have been actively investigated due to their potential application as selectors in crossbar‐array memory [ 1,2 ] and oscillators [ 3–5 ] for neuromorphic computing. Various transition metal oxides such as TiO x , TaO x , VO x , and NbO x were reported to show NDR.…”

Pattern Formation in a RD-MCNN with Locally Active Memristors

“…Nanoscale memristors with locally active (i.e., S-shaped) DC current-voltage (I-V) characteristics have been utilized in the design of oscillatory neuron cells [30,31]. Furthermore, it was shown in [32][33][34] that memristor models in a generic form are capable of representing the dynamics of these nanoscale devices accurately.…”