Investigation of iridium, ruthenium, rhodium, and palladium binary metal oxide solid solution thin films for implantable neural interfacing applications

Metal oxide solid solution thin films containing binary mixtures of iridium, ruthenium, rhodium, and palladium were combinatorially synthesized by DC reactive magnetron sputtering to investigate the compositional dependence of properties relevant to neural interfacing applications. The binary metal oxides studied included Ir_(1-x)M_xO_y where M = Pd, Rh, and Ru. The properties of the binary metal oxides are compared to that of their single metal oxide endmembers which include palladium oxide (PdO_x), ruthenium oxide (RuO_x), rhodium oxide (RhO_x), and iridium oxide (IrO_x). The binary metal oxides exceed the electrochemical performance of their respective single metal oxide endmembers (as measured by cyclic voltammetry) at film thicknesses generally greater than 700 nm. The binary metal oxide concentrations which produce robust microstructures and exceptional electrochemical performance have been identified to be but are not limited to x ≥ 0.5 for Ir_(1-x)Rh_xO_y, x ≥ 0.34 for Ir_(1-x)Ru_xO_y, and x ≥ 0.14 for Ir_(1-x)Pd_x O_y. XPS analyses suggest that the electrochemical enhancements observed are at least partly due to the presence of higher oxidation states in the binary metal oxides when compared to that of the corresponding single metal oxide endmembers.