Electrochemical enhancement of reactively sputtered rhodium, ruthenium, and iridium oxide thin films for neural modulation, sensing, and recording applications

• Published in: Electrochimica acta Vol. 394; p. 139118
• Main Authors: Taylor, Gregory, Paladines, Rhandy, Marti, Anthony, Jacobs, Daaron, Tint, Saxon, Fones, Andrew, Hamilton, Hugh, Yu, Lei, Amini, Shahram, Hettinger, Jeffrey
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 20.10.2021; Elsevier BV
• Subjects: Charge exchange; Chemical composition; Coated electrodes; Crystal structure; Electrochemical analysis; Electrochemical impedance spectroscopy; Equivalent circuit model; High charge storage capacity; Iridium; Magnetron sputtering; Metal oxides; Microelectrodes; Morphology; Neural interfacing electrode; Reactive magnetron sputtering; Recording; Rhodium; Ruthenium oxide; Storage capacity; Thin film; Thin films; RS; Rct; Reactive magnetron sputtering; AFM; Cdl; RuOx; XRD; Al2O3; OPP; Thin film; CSCC; EDS; RhxOy; WO; WP; Rdl; Equivalent circuit model; WT; CPEads; 316-SS; Cfar; ECM; EIS; IrOx; Neural interfacing electrode; CV; CPE; SEM; High charge storage capacity
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2021.139118

Implantable neural interfacing devices are able to diagnose, monitor, and treat many conditions through modulating and recording electrical signals to and from neural tissue. The efficacy of treatment can be limited by a lack of specificity in targeting of neural tissue. To improve specificity and functionality, the electrodes and microelectrode arrays in these devices must be further miniaturized and must possess exceptional charge exchange characteristics. In this study, rhodium oxide (RhxOy), ruthenium oxide (RuOx), and iridium oxide (IrOx) thin films were synthesized using pulsed-DC reactive magnetron sputtering. The effect of sputtering chamber working pressure (WP) on the morphology, crystal structure, chemical composition, and electrochemical properties of the subsequent metal oxide thin films were investigated. The cathodic charge storage capacity (CSCc) and impedance of films were measured via cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), respectively. Results show that CSCc increases, and the overall impedance decreases with increasing WP in all oxide systems. The enhanced electrochemical performance of these films has been attributed in large part to the morphological changes that occur with increasing WP resulting in an apparent increase in the porosity. This study reviews the electrochemical properties of IrOx, and also demonstrates the viability of RhxOy and RuOx as possible electrode coatings for neural interfacing applications.