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

Negative differential resistance (NDR) in NbO x films attracts attention for potential application in neuromorphic computing. A continuous S‐type and abrupt snapback NDR characteristics are reported for NbO x devices. The NDR characteristics are expected to depend on the nature of the switching path in NbO x . Previous NDR studies have been performed mainly on amorphous NbO x films with an electroforming process to create a switching path. Herein, the NDR characteristics of a forming‐free NbO x device with crystalline NbO 2 phases are investigated and these are compared with those of an amorphous NbO x device with forming. The forming‐free NbO x device exhibits a secondary abrupt snapback NDR in addition to the initial S‐type NDR, possibly due to a metal–insulator transition in the NbO 2 phases. Meanwhile, the amorphous NbO x devices only show a continuous S‐type behavior.