Investigation of sputtered iridium oxide as a stimulating/sensing material for neural prostheses

Neural interface devices are developed for neuroscience and neuroprosthetics applications to record and stimulate nerve signals. Microelectrodes represent the direct interface between the biological tissue and the electronic system in neural prostheses that serve to record electrical signals from the nerves to obtain information from the natural sensors of the body or the motor fibers of the muscles. Also, the microelectrodes can inject charge into the targeted tissue to functionally excite nerves and muscles by electrical stimulation. Overall, the neural microelectrodes have to measure electrical potentials and have to exchange charge between the solid state of the electrode and the fluid state of the electrolyte in the body. Therefore, the interface between the microelectrode and biological fluid is a critical factor for the performance of the neural device. The interface properties depend mainly on the physical, electrical and chemical property of the electrode material. Even though a large selection of electrode materials has been tested for this purpose, to date no electrode material or coating process presented in scientific literature has been identified or qualified for long-term stimulation and recording neural signals.;The sputtering pressure was varied to obtain SIROF with desired properties. The SIROF properties were optimized based on its ability to inject charge in the tissue and its mechanical strength. The electrochemical characterization of SIROF was studied by electrochemical impedance spectroscopy (EIS), cyclic voltammetry, (CV), and measuring electrode potential transient while passing a stimulation pulse. SIROF showed low impedance, less than 50 kOhm for typical electrode area of 2 x 10-5 cm2 and high charge injection capacity (∼2 mC/cm2). To determine the damage threshold of the SIROF, inductively coupled mass spectroscopy (ICP-MS), and scanning electron microscopy (SEM) were employed. SIROF demonstrated excellent recording and stimulation characteristics, thereby making it suitable electrode material for neuroprosthetics applications.;In this work, sputtered iridium oxide film (SIROF) was investigated as a potential electrode material. SIROF was deposited on the microelectrodes by reactive pulsed DC sputtering. The deposition parameters and corresponding film properties were examined and correlated with the stimulation and recording characteristics. Furthermore, for chronic applications, the stability of SIROF was investigated and stimulation protocol was determined for damage threshold of the film.