Electrochemical and structural characterizations of electrodeposited iridium oxide thin-film electrodes applied to neurostimulating electrical signal

Thin-film technology takes more and more importance in the development of biomedical devices dedicated to functional neurostimulation. Our research about the design of implantable neurostimulating electrode is oriented toward thin-film cuff electrodes based on PTFE substrate covered by a gold/iridium oxide film. A gold-sputtered film serves as adhesion layer and current collector whereas iridium oxide acts as an electrochemical actuator. The latter is obtained under galvanostatic oxidation and for various electrodeposited charge densities (from 11 to 116 mC/cm2). This paper deals with the design and the characterization of the iridium oxide interfaces and their in vitro application in model nonproteic electrolyte. Microstructural characterization was developed using SEM and AFM. The optimal microstructural organisation was obtained for electrodeposition charge densities from 46 to 70 mC/cm2. The analysis of the interface electrochemical behaviour was carried out by cyclic voltammetry, impedance spectroscopy and square-wave signal. The electrode material shows redox reversible system at 0.5 V/SCE, enabling low-resistance interface and facilitating charge transfer. The optimum electrochemical properties and the optimum microstructure, regarding a biocompatible electrical stimulation, were recorded for electrodeposition charges from 46 to 70 mC/cm2.