Correlation between the transport mechanisms in conductive filaments inside Ta2O5-based resistive switching devices and in substoichiometric TaOx thin films

Abstract

Conductive filaments play a key role in redox-based resistive random access memory (ReRAM) devices based on the valence change mechanism, where the change of the resistance is ascribed to the modulation of the oxygen content in a local region of these conductive filaments. However, a deep understanding of the filaments' composition and structure is still a matter of debate. We approached the problem by comparing the electronic transport, at temperatures from 300 K down to 2 K, in the filaments and in TaOx films exhibiting a substoichiometric oxygen content. The filaments were created in Ta (15 nm)/Ta2O5 (5 nm)/Pt crossbar ReRAM structures. In the TaOx thin films with various oxygen contents, the in-plane transport was studied. There is a close similarity between the electrical properties of the conductive filaments in the ReRAM devices and of the TaOx films with x ∼ 1, evidencing also no dimensionality difference for the electrical transport. More specifically, for both systems there are two different conduction processes: one in the higher temperature range (from 50 K up to ∼300 K), where the conductivity follows a T dependence, and one at lower temperatures (<50 K), where the conductivity follows the exp(−1/T) dependence. This suggests a strong similarity between the material composition and structure of the filaments and those of the substoichiometric TaOx films. We also discuss the temperature dependence of the conductivity in the framework of possible transport mechanisms, mainly of those normally observed for granular metals.