*Gregory Taylor¹, Saxon Tint², Andrew Fones³, Lei Yu¹, Hugh Hamilton³, Shahram Amini^1,4,5, Jeffrey Hettinger^1
1Rowan University, Glassboro, NJ; ²Johnson Matthey Inc., San Diego, CA; ³Johnson Matthey Inc., Reading, United Kingdom; ⁴Johnson Matthey Inc., West Chester, PA; ⁵Now with Pulse Technologies, Quakerstown, PA
In this work, electrochemical performance of single, binary, and ternary oxide thin films of the platinum group metals (PGM) iridium, rhodium, palladium, and ruthenium are investigated for the first time as electrode coatings for neural interface applications. Over the past few decades, several materials have been examined as coatings for the continued miniaturization and development of electrode systems for improved sensing, recording of neurological activity and stimulating of nerve tissue. When implanted in the body, these electrodes, as an essential component of a neurostimulation device, are intended to treat, diagnose and understand diseases, disorders, and injuries. For longterm implantable neurostimulation devices, iridium oxide (IrO_x) coatings have been investigated by several groups due to their charge injection characteristics, charge storage capacity (CSC), and biocompatibility. However, as demonstrated in this work, these favorable properties are not limited to IrO_x. The current study complements earlier research by investigating how various deposition parameters influence the CSC of the single metal oxide systems of not only IrO_x, but rhodium oxide (RhO_x), palladium oxide (PdO_x), and ruthenium oxide (RuO_x). More importantly, this work also examines how charge storage characteristics vary or improve significantly based on compositional makeup of binary and ternary solid solutions of IrO_x, RhO_x, PdO_x, and RuO_x under similar experimental conditions. The results demonstrate that properties such as preferred orientation, microstructure, and charge storage capacity (CSC) can be tuned and enhanced to varying degrees in both the single oxides and solid solution systems. Last but not least, solid solution systems demonstrate enhanced CSC over their single oxide endmembers and exhibit a positive charge storage-thickness dependence under certain deposition conditions as measured by cyclic voltammetry in phosphate buffered saline solution.