Metallic filamentary conduction in valence change-based resistive switching devices: the case of TaOx thin film with x∼ 1.

The resistive switching in metal-oxide thin films typically occurs via modulation of the oxygen content in nano-sized conductive filaments. For Ta2O5-based resistive switching devices, the two current models consider filaments composed of oxygen vacancies and those containing metallic Ta clusters. The present work tries to resolve this dispute. The filaments in Ta2O5 were formerly shown to exhibit the same electrical transport mechanisms as TaOx thin films with x∼ 1.0. In this paper, sputtered thin films of pure β-Ta and of TaOx with different oxygen concentrations are studied and compared in terms of their structure and electrical transport. The structural analysis reveals the presence of Ta clusters in the TaOx films. Identical electrical transport characteristics were observed in the TaOx films with x∼ 1.0 and in the β-Ta film. Both show the same transport mechanism, a carrier concentration on the order of 1022 cm-3 and a positive magnetoresistance associated with weak antilocalization at T < 30 K. It is concluded that the electrical transport in the TaOx films with x∼ 1.0 is dominated by percolation through Ta clusters. This means that the transport in the filaments is also determined by percolation through Ta clusters, strongly supporting the metallic Ta filament model.