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

Negative differential resistance (NDR) in NbOx films attracts attention for potential application in neuromorphic computing. A continuous S‐type and abrupt snapback NDR characteristics are reported for NbOx devices. The NDR characteristics are expected to depend on the nature of the switching path in NbOx. Previous NDR studies have been performed mainly on amorphous NbOx films with an electroforming process to create a switching path. Herein, the NDR characteristics of a forming‐free NbOx device with crystalline NbO2 phases are investigated and these are compared with those of an amorphous NbOx device with forming. The forming‐free NbOx device exhibits a secondary abrupt snapback NDR in addition to the initial S‐type NDR, possibly due to a metal–insulator transition in the NbO2 phases. Meanwhile, the amorphous NbOx devices only show a continuous S‐type behavior.