This paper investigates the origin of the threshold switching effect in niobium oxide based filamentary switching cells.

This work elucidates some aspects of the nonlinear dynamics of a thermally-activated locally-active memristor based on a micro-structure consisting of a bi-layer of and materials. Through application of techniques from the theory of nonlinear dynamics to an accurate and simple mathematical model for the device, we gained a deep insight into the mechanisms at the origin of the emergence of local activity in the memristor. This theoretical study sets a general constraint on the biasing arrangement for the stabilization of the negative differential resistance effect in locally active memristors and provides a theoretical justification for an unexplained phenomenon observed at HP labs. As proof-of-principle, the constraint was used to enable a memristor to induce sustained oscillations in a one port cell. The capability of the oscillatory cell to amplify infinitesimal fluctuations of energy was theoretically and experimentally proved.

Resistive switching devices with a Nb2O5/NbOx bilayer stack combine threshold and memory switching. Here we present a new fabrication method to form such devices. Amorphous Nb2O5 layers were treated by a krypton irradiation. Two effects are found to turn the oxide partly into a metallic NbOx layer: preferential sputtering and interface mixing. Both effects take place at different locations in the material stack of the device; preferential sputtering affects the surface, while interface mixing appears at the bottom electrode. To separate both effects, devices were irradiated at different energies (4, 10, and 35 keV). Structural changes caused by ion irradiation are studied in detail. After successful electroforming, the devices exhibit the desired threshold switching. In addition, the choice of the current compliance defines whether a memory effect adds to the device. Findings from electrical characterization disclose a model of the layer modification during irradiation.

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