Insulation of thin-film parylene-C/platinum probes in saline solution through encapsulation in multilayer ALD ceramic films.

The long-term electrical leakage performance of parylene-C/platinum/parylene-C (Px/Pt/Px) interconnect in saline is evaluated using electrochemical impedance spectroscopy (EIS). Three kinds of additional ceramic encapsulation layers between the metal and Px are characterized: 50 nm-thick alumina (AlO), 50 nm-thick titania (TiO), and 80 nm-thick AlO-TiO nanolaminate (NL). The AlO and TiO encapsulation layers worsen the overall insulation properties. The NL encapsulation layer improves the insulation when combined with a TiO outer layer to promote adhesion to the Px. Experiments are performed with various insulation promotion treatments: A-174 silane (A174) treatment before Px deposition (to promote adhesion); SF plasma treatment (F) after Px deposition (to increase hydrophobicity); and ion-milling descum (IM) after Px deposition (to prevent parylene oxidation). A174 and F treatments do not have a significant impact, while IM leads to worse insulation performance. A circuit model elucidates the insulation characteristics of Px-ceramic-Pt-ceramic-Px interconnect. These studies provide a foundation for processing ultra-compliant neural probes with long-term chronic utility.