Doping controlled resistive switching dynamics in transition metal oxide thin films

Abstract

Transition metal oxide thin films have attracted increasing attention due to their potential in non-volatile resistive random access memory (RRAM) devices, where such thin films are used as active layers in metal-insulator-metal (MIM) configurations. Titanium dioxide is one of the most celebrated oxides among the ones that exhibit resistive switching behaviour due to its wide band gap, high thermal stability, and high dielectric constant. RRAM devices with various materials as active layers, have demonstrated very fast switching performance but also huge potential for miniaturisation, which is the bottleneck of FLASH memory. Nevertheless, these devices very often suffer poor endurance, physical degradation, large variability of switching parameters and low yields. In most cases, the physical degradation stems from high electroforming and switching voltages. Doping of the active layer has been often employed to enhance the performance of RRAM devices, like endurance, OFF/ON ratio, forming voltages, etc. In this work, doping in TiO2-x RRAM devices was used to engineer the electroforming and switching thresholds so that device degradation and failure can be delayed or prevented. Al and Nb were selected with basic criteria the ionic radius and the oxidation state. The doped RRAM devices, showed improved switching performance compared to their undoped counterparts. Alternative approaches to doping were also investigated, like multilayer stacks comprising Al₂O_3-y and TiO_2-x thin films. Furthermore, Al:TiO_2-x/Nb:TiO_2-x bilayer RRAM devices were fabricated, to prove whether a diode behaviour of the p-n interface inside the RRAM was feasible. The latest would be a particularly interesting finding towards active electronics.

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Identifiers

ORCID for Themis Prodromakis: orcid.org/0000-0002-6267-6909

ORCID for Giampaolo D'alessandro: orcid.org/0000-0001-9166-9356

ORCID for Sakellaris Mailis: orcid.org/0000-0001-8100-2670

ORCID for Nina Podoliak: orcid.org/0000-0002-3146-0355

ORCID for Spyros Stathopoulos: orcid.org/0000-0002-0833-6209

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