Charge injection properties of iridium oxide films produced on Ti-6Al-4V alloy substrates by ion beam mixing techniques

Abstract

The charge injection capabilities of iridium oxide films, as produced on Ti-6Al-4V alloy substrates by ion-beam mixing techniques, were investigated. Iridium oxide is a valence change oxide, and therefore has high values of charge injection density upon voltage cycling in electrolytes. Because of this property, iridium oxide films are useful as working elements in neural prostheses. Iridium films of three thicknesses, produced by sputter deposition followed by ion beam mixing, were tested in cyclic voltammetry out of 1000 cycles or more. Two surface preparations, mechanical polishing and an acid passivation treatment, were also used as controls. Surface analysis was primarily by Rutherford backscattering spectrometry. Both the ion-beam mixing and the acid pretreatment increased the lifetimes of films, in comparison with the mechanically polished standards. Reductions in charge injection capability, when they occurred, were attributed to loss of iridium from the films, and there was a close correlation between the charge injection density and the iridium inventory.