RF-sputtering of iridium oxide to be used as stimulation material in functional medical implants

This paper describes the reactive RF-powered sputter deposition of iridium oxide (IrOx) to be used as the active stimulation layer in functional medical implants. Using an approach based on generic curves, the amount of oxygen gettered by the film is determined for various carrier gas flows and pumping speeds. It is shown that under certain conditions the getter effect peaks in the shape of a plateau when increasing the oxygen supply to the chamber. Films deposited along this curve show strong differences in electrochemical behaviour. At the beginning of the plateau, stable films with high electrochemical activity are deposited, and impedance measurements link the increase in charge delivery to a higher active surface area. On depositing at the far side of the plateau, the maximum deposition rate is recorded; however, unstable films are formed. These films predominantly contain unstable iridium oxide species, with iridium atoms in higher valence states. Protein adsorption, as is known to occur at implanted electrodes, was tested on some samples, and does not deteriorate the IrOx characteristics.