Electrodeposition and Characterization of Thin-Film Platinum-Iridium Alloys for Biological Interfaces

Abstract

An efficient platinum-iridium thin film alloy electrodeposition method has been evaluated to modify the surface of platinum or gold microelectrodes that are being developed for neural recording and stimulation applications. A large number of electrodeposition process variables have been investigated in terms of how they affected the properties of the electrodeposited films. Three sets of Pt-Ir films of a certain composition were electroplated on gold substrates using a potential cycling technique and characterized using microscopy, elemental analysis, nanoindentation, and electrochemical techniques to evaluate the repeatability of the electrodeposition process. Deposition rates were estimated by determining film mass and thickness as a function of deposition time. The surface morphology of the Pt-Ir films was characterized using scanning electron microscopy (SEM) and the chemical composition was determined using wavelength dispersive spectroscopy (WDS). Nanoindentation measurements showed that the hardness of the electroplated Pt-Ir thin films was nearly 100% higher than that of a Pt foil. The electrochemical properties of the films were evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) and compared with those of pure Pt, pure Ir and 80–20% Pt-Ir foils. The final electroplating process resulted in 60–40% Pt-Ir alloys. The film thickness increased with electrodeposition time at a rate of 16.5 nm/min and stable films with up to 500 nm thickness were obtained. Characterization by SEM and EIS revealed that the real surface area of the Pt-Ir films was much larger than that of pure Pt and increased significantly with increasing deposition time.