Characterization of Parylene-C Film as an Encapsulation Material for Neural Interface Devices

Jui-Mei Hsu(a), Sascha Kammer(b), Erik Jung(c), Loren Rieth(d), A. Richard Normann(e), Florian Solzbacher(a)(d)(e)
a: Department of Material Science and Engineering, University of Utah, Salt Lake City, UT, USA
b: Fraunhofer IBMT, St. Ingbert, Germany
c: Fraunhofer IZM, Berlin, Germany
d: Department of Electrical Engineering, University of Utah, Salt Lake City, UT, USA
e: Department of Bioengineering, University of Utah, Salt Lake City, UT, USA

Abstract

Neural interfaces, devices that interact with nervous system, have been developed to help patients with neural disorders to restore lost neural function. The neural interface device requires a conformal and biocompatible encapsulation layer to protect the device during chronic implantation, and to electrically isolate individual electrodes. Parylene-C thin films deposited by a chemical vapour deposition system were studied as an encapsulation layer for neural interface devices. Leakage current tests were used to investigate the encapsulation performance of Parylene-C films, and the results showed hermetic protection as well as long-term (>100 days) stability of the films. The adhesion between Parylene-C and the silicon substrate after several thermal treatments was studied by ASTM tape adhesion tests. Results from these tests suggested that thermal stress may degrade the adhesion force. Parylene samples were subjected to accelerated lifetime testing (85 % relative humidity (RH) and 85 °C) for 20 days, and the film did not show appearance changes as observed by optical microscopy. However, X-ray diffractograms show that the film crystallinity increased during this test.