Sputtered Iridium Oxide as Electrode Material for Subretinal Stimulation

Sputtered Iridium Oxide as Electrode Material for Subretinal Stimulation
Haas J, Rudorf R, Becker M, Daschner R, Drzyzga A, Burkhardt C, Stett A
Sensors and Materials, Vol. 32, No. 9 (2020) 2903–2918, https://doi.org/10.18494/SAM.2020.2903

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/cm2), and high CIC (4.2 mC/cm2). 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