Sputtered Iridium Oxide as Electrode Material for Subretinal Stimulation

Abstract

The efficiency and safety of neuronal stimulation with implants strongly depend on the electrode material. Microelectrodes composed of iridium oxide are becoming increasingly important as they exhibit excellent charge injection capacity (CIC) as well as charge storage capacity (CSC). We present the development of a robust process for the fabrication of sputtered iridium oxide films (SIROF). This process has been used for the "RETINA IMPLANT Alpha AMS" for several years of subretinal stimulation. In this paper, we describe the full experimental investigation of the electrode material. The electrochemical and morphological properties were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), voltage transient measurements, and focused ion beam-scanning electron microscopy (FIB-SEM). The implementation on the CMOS chip of the retinal prosthesis is presented. The deposition process window was investigated extensively. Major changes in process parameters lead to a difference in impedance of only 10% of the mean. Accelerated aging tests revealed a long-term stability of the electrodes of at least 10 years under conditions of use. The SIROF electrodes (diameter 30 µm) show low impedance (15.9 kΩ), excellent CSC (50.9 mC/cm 2), and high CIC (4.2 mC/cm 2). In summary, the robustness of the presented deposition process and the large process window enable the integration of high-quality SIROF microelectrodes in active implants and thus long-term stability in a wide range of safe electrical stimulation.

Minimizing Iridium Oxide Electrodes for High Visual Acuity Subretinal Stimulation

“…The electrode polarization limit is known as the water window and occurs at −0.6V for cathodal stimulation and 0.8 V for anodal stimulation for SIROF electrodes. The measured charge injection limit of sputtered iridium oxide electrodes was 3.3 ± 0.2 mC/cm 2 , also within the range of previously reported studies of SIROF ( Cogan, 2008 ; Cogan et al, 2009 ; Haas et al, 2020 ; Negi et al, 2012 ). The total safe injectable charge per stimulation pulse scales with area, equaling 2.5, 10, and 25 nC for 10, 20, and 30 μm electrodes, respectively ( Fig.…”

Advanced Metallic and Polymeric Coatings for Neural Interfacing: Structures, Properties and Tissue Responses

“…The structure and properties of IrO x are different based on the fabrication methods [ 91 ]. There are many kinds of iridium oxide, including sputtered iridium oxide film (SIROF) ( Figure 3 a) [ 85 , 87 , 91 , 92 , 93 , 94 ], electrodeposited iridium oxide film (EIROF) ( Figure 3 b) [ 84 , 95 , 96 , 97 , 98 ], activated iridium oxide film (AIROF) ( Figure 3 c) [ 86 , 99 , 100 , 101 , 102 ], atomic-layer-deposited iridium oxide film [ 103 ], and physical-vapor-deposited iridium oxide film [ 104 ]. A porous iridium oxide layer could be observed for AIROF and EIROF, while SIROF showed a dendritic surface structure.…”

Ferroelectricity and resistive switching in BaTiO$_3$ thin films with liquid electrolyte top contact for bioelectronic devices

“…As a consequence, neuroprosthetic devices are typically based on conductive microelectrodes. For example, state-of-the-art retinal implants to restore vision in blind patiens are based on conductive microelectrodes consisting of Pt [14] or sputtered IrOx [15,16].…”