Thermal Stability of a RuO₂ Electrode Prepared by DC Reactive Sputtering

RuO₂ films were deposited by reactive DC sputtering, and the formation process and the thermal stability were investigated. In the RuO₂/Ti/SiO₂ structure, the Ti surface was preferentially oxidized at the initial stage of RuO₂ growth. Insertion of Ru and TiN layers between the RuO₂ and Ti layers can suppress the oxygen diffusion toward the Ti layer during the film growth. However, when the RuO₂/Ru/TiN/Ti/Si structure was heat-treated, the RuO₂ was partially reduced to form RuO_2-X and the TiN was oxidized to TiO₂ while generating N₂ and O₂ gases, resulting in voids formation at the RuO₂/Ru interface, regardless of the heat-treatment atmosphere. We found this was caused by internal oxygen diffusion within the stacked layers. This reaction is governed by the transference of oxygen to the TiN and Ti layers by the difference in the Gibbs' formation free energy, and by the oxygen diffusion enhancement.