This study investigates resistive switching in amorphous undoped and Cr-doped vanadium oxide thin films synthesized by sputtering deposition at low oxygen partial pressure. Two different volatile threshold switching characteristics can occur as well as a non-volatile bipolar switching mechanism, depending on device stack symmetry and Cr-doping. The two threshold switching types are associated with different crystalline phases in the conduction filament created during an initial forming step. The first kind of threshold switching, observed for undoped vanadium oxide films, was, by its temperature dependence, proven to be associated with a thermally triggered insulatorto-metal transition in a crystalline VO 2 phase, whereas the threshold switch observed in chromium doped films is stable up to 90 C and shows characteristics of an electronically induced Mott transition. This different behaviour for undoped versus doped films has been attributed to an increased stability of V 3þ due to the Cr 3þ doping (as evidenced by X-ray photoelectron spectroscopy analysis), probably favouring the creation of a crystalline Cr-doped V 2 O 3 phase (rather than a Cr-doped VO 2 phase) during the energetic forming step. The symmetric Pt/a-(VCr)O x /Pt device showing high temperature stable threshold switching may find interesting applications as a possible new selector device for resistive switching memory (ReRAM) crossbar arrays.

In this paper, we want to review the correlation between filamentary (width) switching and the (SET) I–V characteristics by discussing the existing models.

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