Morphology and Electrochemical Properties of Activated and Sputtered Iridium Oxide Films for Functional Electrostimulation

Iridium oxide (IrOx) has attracted much attention for neural interface applications due to its ability to transfer between ionic and electronic current and to resist corrosion. The physical, mechanical, chemical, electrical and optical properties of thin films depend on the method and parameters used to deposit the films. In this report, the surface morphology, impedance and charge capacity of activated iridium oxide film (AIROF) and sputtered iridium oxide film (SIROF) were investigated in vitro and compared. The Utah Electrode Array (UEA) having similar electrode area and shape were employed in this study. The electrode coated with AIROF and SIROF were characterized by scanning electron microcopy, cyclic voltammetry, electrochemical impedance spectroscopy and potential transient measurements to measure charge injection capacity (CIC). SIROF and AIROF selectively deposited on electrode tip had dendrite and granular microstructure, respectively. The CIC of unbiased SIROF and AIROF was found to be 2 and 1 mC/cm2, respectively, which is comparable to other published values. The average impedance, at a frequency of 1 kHz was ~65 and ~7 kΩ for the AIROF and SIROF, respectively. Low impedance and high CIC makes SIROF highly recommended stimulation and recording material.