Thin film flexible electrodes based on gold/polytetrafluoroethylene layers

Thin film gold electrodes on flexible Polytetrafluoroethylene (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 (AC) impedance measurements show a linear relationship between the reactive component of the impedance and the surface roughness. Surface features below 42 nm root mean square deviation from the average surface height are shown to result in a reduction in interface impedance and improved impedance matching to a 1% NaCl solution. The surface roughness of the gold is controlled using an electrolytic etch in a NaCl solution allowing the electrical characteristics of the interface to be influenced. Plasma modification of the PTFE substrate is seen to increase the surface energy by changing the chemical nature of the polymer and lead to enhanced adhesion of the gold layers. Applications of such techniques are expected to improve the current design of physiological signal sensors as well as enhance the reproducibility of biosensing devices