Bond nature of active metal ions in SiO2-based electrochemical metallization memory cells

Abstract

Electrochemical metallization cells are candidates for the next-generation non-volatile memory devices based on resistive switching. Despite the intensive studies in recent years a microscopic model of the processes in these nanoscale electrochemical systems is still missing and the physicochemical properties of the active metal ions have been rarely reported. We examined the bonding characteristics of Cu^z+ and Ag⁺ ions in SiO₂-based cells using soft X-ray absorption spectroscopy. Whereas the Ag/SiO₂ interfaces showed no chemical interaction of Ag ions, the Cu/SiO₂ showed clear signatures of partial oxidation into two ionic species of Cu²⁺ and Cu⁺. The analyses on the orbital hybridization strength evidently showed that the Cu²⁺–O²⁻ bonds in SiO₂ are much weaker than the Cu⁺–O²⁻ bonds, analogous to the case of bulk CuO and Cu₂O. This suggests that the Cu²⁺ ions should be more mobile and with a dominating role in the process of resistive switching.