Charge Injection Properties of Thermally-Prepared Iridium Oxide Films

Multilayered Ir oxide films were prepared on Ti and Pt:Ir electrodes by the thermal decomposition of successive layers of alcohol solutions of IrCl 3 . The charge capacity of the thermally-formed Ir oxide films (TIROF) and the reversibility of surface oxide-related reactions were evaluated in a physiological saline solution using potential sweep and current pulse techniques. The TIROF-coated electrodes had electrochemical properties similar to an Ir electrode coated with an anodically-formed oxide. The charge injection limits before gassing ranged from 5–10 mC/cm 2 for TIROF-Ti and 1–3 mC/cm 2 for TIROF-Pt:Ir with biphasic, charge-balanced current pulses of 0.2 ms duration. No Pt dissolution was detected during >100 hr stimulation with TIROF-Pt:Ir electrodes. Small amounts of Ir dissolution were detected which might result from passive leaching of residual chloride complexes of Ir. The TIROF coatings remained firmly attached to the substrate metal during long term pulsing and abrasion tests. The properties of TIROF coatings, e.g., high charge capacity for reversible charge injection and good abrasion and corrosion resistance, are of great advantage for neural prosthesis applications.