Thin films and microelectrode arrays for neuroprosthetics

Complex prosthetic limbs, the bionic eye, or brain-computer interfaces implement microelectrode arrays to connect the nervous system to an electronic device. The aim is to partly restore lost body functions or to gather bioelectrical activity from the nervous system. Microelectrode arrays are fabricated to have specifi c electrical and mechanical properties to match the biological requirements of the intended application. Polyimide and parylene-C are favorable polymers for substrate and insulation layers in thin-fi lm applications. This article reviews the materials and the mechanical and electrical properties of electrode arrays. It emphasizes the often ignored but crucial infl uence of adhesion of the thin-fi lm layers on the device’s longevity and reliability. Adhesion promotion techniques using layers of silicon carbide (SiC) are also discussed. Even though the main focus is on thin-fi lm devices fabricated using traditional methods of micromachining based on lithography, an alternative to thin fi lms, laser-patterned silicone/metal foil microelectrode arrays, is also presented. Characterization as well as application examples of these devices are also presented.