Metallic filamentary conduction in valence change-based resistive switching devices: the case of TaO 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 TaO-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 TaO were formerly shown to exhibit the same electrical transport mechanisms as TaO thin films with x∼ 1.0. In this paper, sputtered thin films of pure β-Ta and of TaO 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 TaO films. Identical electrical transport characteristics were observed in the TaO films with x∼ 1.0 and in the β-Ta film. Both show the same transport mechanism, a carrier concentration on the order of 10 cm and a positive magnetoresistance associated with weak antilocalization at T < 30 K. It is concluded that the electrical transport in the TaO 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.