Different threshold and bipolar resistive switching mechanisms in reactively sputtered amorphous undoped and Cr-doped vanadium oxide thin films

Abstract

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 Situ Nanostructural Analysis of Volatile Threshold Switching and Non‐Volatile Bipolar Resistive Switching in Mixed‐Phased a‐VOx Asymmetric Crossbars

“…Furthermore, there is a movement of vanadium and oxygen ions to form a low resistive path as can be seen in Figure 5 and Table 2. [11,28] The switching mechanism for volatile TS is summarized in Figure 6. [11,28] The switching mechanism for volatile TS is summarized in Figure 6.…”

“…[11] They attributed the occurrence of BRS mainly to the asymmetric device structure, while TS to symmetric device structure. [11] They attributed the occurrence of BRS mainly to the asymmetric device structure, while TS to symmetric device structure.…”

“…[2] Complex class of vanadium oxide spans a broad range of 20 phases. [11][12][13] Apolar TS property in the above papers is desirable as a selector element in crossbar arrays to reduce the sneak-path current (which disrupts stored data). [11][12][13] Apolar TS property in the above papers is desirable as a selector element in crossbar arrays to reduce the sneak-path current (which disrupts stored data).…”

“…For this reason, a few recent studies [10,[14][15][16] demonstrated TS based on amorphous vanadium oxide (a-VO x ). We choose amorphous films because crystalline films are porous due to grain boundaries and pin-holes, [11] which is unsuitable for stacked architectures. This variability highlights that nanostructural investigations are needed to understand the origins of different memory behaviors, in particular the reasons for observing volatile and apolar TS in a-VO x films for its practical utilization as a selector element.…”

“…We choose amorphous films because crystalline films are porous due to grain boundaries and pin-holes, [11] which is unsuitable for stacked architectures. We further introduce a fabrication procedure (Section S1, Supporting Information) to incorporate a-VO x in crossbar architecture, which has been found to dissolve in water.…”