Coexistence of memory and threshold resistive switching identified by combinatorial screening in niobium-tantalum system

Abstract

Memristive devices exhibiting improved performance and memory characteristics are revealed by using a combinatorial screening approach. An Nb-Ta thin film library, with a total compositional spread ranging between 13 and 80 at.% Ta, is co-sputtered as the bottom electrode, while their anodic oxides served as active layers. Such metal–insulator-metal (MIM) specimens under investigation are finalized with patterned Pt top electrodes. Memristors based on mixed Nb2O5-Ta2O5 have been grouped according to their common switching characteristics in four different compositional zones. Reversible switching between threshold and non-volatile mode was observed for devices grown on Nb-39 at.% Ta alloy. The switching mode was dictated by applying different current compliances. Moreover, devices based on Nb-36 at.% Ta switch at minimum seven distinct resistive levels. Apart from the electrical measurements, the structure of samples and components distribution in cross-section geometry is studied via TEM techniques before and after electrical treatment. Electrolyte incorporation and the exact composition of the identified high-performance memristors (resulting from the combinatorial screening) are analyzed by HAXPES. The memristive devices based on the two singled-out Nb-Ta alloys show enhanced memory and electrical characteristics, thus being excellent candidates for neuromorphic applications.