A novel surface modification method to achieve low impedance neural microelectrode arrays

Advances in neuroprostheses are strongly dependent on the development of microelectrodes with an enhanced ability to selectively record or stimulate neural signals. Selectivity for a microelectrode depends on its ability to interact with a small number of neurons and/or nerve fibers. In order to achieve selective electrical transduction, the surface area of active site should be on the order of tens of micrometers. However, as the area of the electrode decreases, the electrode impedance increases, which in turn affects the recording/stimulating characteristics (sensitivity). Thus there is a trade-off between selectivity and sensitivity. One option to overcome this trade-off is by generating a large functional active area without increasing the geometrical surface area (GSA) of the electrodes. This paper for the first time reports a novel method of using a combination of SF₆ and O₂ based reactive ion etching (RIE), to modify the surface of electrodes tip, in order to increase the RSA without increasing the GSA. The study demonstrates that by altering the surface morphology of the electrode tips, the impedance can be lowered significantly. The optimum etching power was 250 W which yielded mechanically robust, high charge storage capacity (CSC), and low electrochemical impedance surface.