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Devices exploiting negative differential resistance (NDR) are of particular interest for analog computing applications, including oscillator‐based neural networks. These devices typically exploit the continuous S‐shaped current–voltage characteristic produced by materials with a strong temperature‐dependent electrical conductivity, but recent studies have also highlighted the existence of a second, discontinuous (snap‐back) characteristic that has the potential to provide additional functionality. The development of devices based on this characteristic is currently limited by uncertainty over the underlying physical mechanism, which remains the subject of active debate. In situ thermoreflectance imaging and a simple model are used to finally resolve this issue. Specifically, it is shown that the snap‐back response is a direct consequence of current localization and redistribution within the oxide film, and that material and device dependencies are consistent with model predictions. These results conclusively demonstrate that the snap‐back characteristic is a generic response of materials with a strong temperature‐dependent conductivity and therefore has the same physical origin as the S‐type characteristic. This is a significant outcome that resolves a long‐standing controversy and provides a solid foundation for engineering functional devices with specific NDR characteristics. [ABSTRACT FROM AUTHOR]

Devices exploiting negative differential resistance (NDR) are of particular interest for analog computing applications, including oscillator‐based neural networks. These devices typically exploit the continuous S‐shaped current–voltage characteristic produced by materials with a strong temperature‐dependent electrical conductivity, but recent studies have also highlighted the existence of a second, discontinuous (snap‐back) characteristic that has the potential to provide additional functionality. The development of devices based on this characteristic is currently limited by uncertainty over the underlying physical mechanism, which remains the subject of active debate. In situ thermoreflectance imaging and a simple model are used to finally resolve this issue. Specifically, it is shown that the snap‐back response is a direct consequence of current localization and redistribution within the oxide film, and that material and device dependencies are consistent with model predictions. These results conclusively demonstrate that the snap‐back characteristic is a generic response of materials with a strong temperature‐dependent conductivity and therefore has the same physical origin as the S‐type characteristic. This is a significant outcome that resolves a long‐standing controversy and provides a solid foundation for engineering functional devices with specific NDR characteristics. [ABSTRACT FROM AUTHOR]

Metal-oxide-metal (MOM) devices based on niobium oxide exhibit threshold switching (or current-controlled negative differential resistance) due to thermally induced conductivity changes produced by Joule heating. A detailed understanding of the device characteristics therefore relies on an understanding of the thermal properties of the niobium oxide film and the MOM device structure. In this study, we use time-domain thermoreflectance to determine the thermal conductivity of amorphous NbO x films as a function of film composition and temperature. The thermal conductivity is shown to vary between 0.86 and 1.25 W·m -1 ·K -1 over the composition ( x = 1.9 to 2.5) and temperature (293 to 453 K) ranges examined, and to increase with temperature for all compositions. The impact of these thermal conductivity variations on the quasistatic current-voltage ( I - V ) characteristics and oscillator dynamics of MOM devices is then investigated using a lumped-element circuit model. Understanding such effects is essential for engineering functional devices for nonvolatile memory and brain-inspired computing applications.