Electroforming and threshold switching characteristics of NbOx films with crystalline NbO2 phase

Abstract

Threshold switching (TS) and negative differential resistance (NDR) characteristic of niobium oxide (NbOx) films have been actively studied for neuromorphic computing. Generally, the electroforming process is required for TS and NDR in NbOx films. However, different electroforming and TS properties have been reported for NbOx films with different crystallinities or chemical compositions. This study investigates the effect of thermal annealing on the microstructures of NbOx films and compares the electroforming, TS, and NDR characteristics of amorphous, partially crystallized, and fully crystallized films. The distributions of crystalline NbO2 phase in NbOx films annealed at various temperatures were analyzed using transmission electron microscopy dark-field imaging, and it was observed that the distribution of crystalline NbO2 phase influenced the electroforming process. Moreover, TS characteristics improved in the thermally annealed NbOx films with crystalline NbO2 phases.