Hybrid laser and reactive ion etching of Parylene-C for deinsulation of a Utah electrode array

Electrodes used for neural interfaces are typically encapsulated by biocompatible materials such as Parylene-C. Tips of a Utah electrode array (UEA) for recording neural action potentials are typically exposed using a reactive ion etching (RIE); however, it has limitations due to the complex 3D geometry of electrode arrays, resulting in nonuniformity of deinsulated area, difficulty in achieving very fine tip exposure, and decrease in selectivity in acquiring the neural signals. The laser ablation technique can be used to deinsulate electrode tips with exposures smaller than 20 µm. However, the electrode arrays suffer from increased impedance due to redeposition of the carbon debris produced by the ablation of the Parylene-C on the active area of the electrodes. The hybrid laser and plasma etching uses a laser (KrF) ablation followed by an oxygen reactive ion etching process to better control tip exposure, particularly for electrode arrays with more complex geometries, and a lower electrode impedance at the same time. Characterization of the deinsulated electrode surface by scanning electron microscope (SEM), x-ray photoelectron spectroscopy (XPS) and impedance of a Utah electrode array (UEA) suggests that the hybrid laser/RIE method is suitable for deinsulation of UEAs for neural interface applications. (paper)