Surface modification of thin film gold electrodes for improved in vivo performance

Thin film gold electrodes on flexible PTFE substrates are produced for medical implantation. The electrical interface impedance of the electrodes is measured in vitro as a function of surface roughness of the gold as quantified using atomic force microscopy. Alternating current impedance measurements show a linear relationship between the reactive component of the impedance and the surface roughness. Surface features below a few tens of nanometres root mean square deviation from the average surface height are shown to result in a reduction in interface impedance and improved matching to a 1% NaCl solution. The surface roughness of the gold is controlled using an electrolytic etch in an NaCl solution which causes electropitting and therefore allows the electrical characteristics of the interface to be influenced.