Liu, XinjunZhang, PengNath, Shimul KantiLi, ShuaiNandi, SanjoyElliman, Robert2024-03-070022-3727http://hdl.handle.net/1885/315786Volatile memristors, or threshold switching devices, exhibit a diverse range of negative differential resistance (NDR) characteristics under current-controlled operation and understanding the origin of these responses is of great importance for exploring their potential as nano-scale oscillators for neuromorphic computing. Here we use a previously developed two-zone, parallel memristor model to undertake a systematic analysis of NDR modes in two-terminal metal-oxide-metal devices. The model assumes that the non-uniform current distribution associated with filamentary conduction can be represented by a high current density core and a lower current-density shell where the core is assumed to have a memristive response due to Poole-Frenkel conduction and the shell is represented by either a fixed resistor or a second memristive region. A detailed analysis of the electrical circuits is undertaken using a lumped-element thermal model of the core-shell structure, and is shown to reproduce continuous and discontinuous NDR responses, as well as more complex compound behaviour. Finally, an interesting double-window oscillation behaviour is predicted and experimentally verified for a device with compound NDR behaviour. These results clearly identify the origin of different NDR responses and provide a strong basis for designing devices with complex NDR characteristics.This work was partly funded by the National Natural Science Foundation of China (Nos. 11674241 and 11774253) and Natural Science Foundation of Tianjin City (No. 18JCYBJC18000). The authors also acknowledge funding from the Australian Research Council (ARC) Linkage Project (LP150100693) and Varian Semiconductor Equipment/Applied Materials.application/pdfen-AU© 2021 IOP Publishing Ltdnegative differential resistancethreshold switchingniobium oxidevolatile memristorcore–shell modeloscillatorneuromorphic computing202110.1088/1361-6463/ac3bf42022-10-16