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M. D. Gingerich, D. B. Shire, S. F. Cogan, T. Plante, J. L. Wyatt, J. F. Rizzo; A Microfabricated Subretinal Electrode Array With an Integrated a-SiC Barrier. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3040.
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This work is related to the efforts of the Boston Retinal Implant Project to develop a subretinal prosthesis to restore vision to the blind. The specific purpose of this presentation is to describe our efforts to increase the projected lifetime of our polyimide-based microfabricated electrode arrays by integrating an amorphous-silicon carbide (a-SiC) barrier around the signal conductors.
A base polyimide layer was spin-coated and cured on a Si substrate. A layer of a-SiC was deposited by plasma enhanced chemical vapor deposition (PECVD) followed by the evaporation deposition of a patterned conductor metal stack (Ti/Au/Ti). A second a-SiC layer was deposited over the metal, pad/site openings were dry-etched through the a-SiC to the metal by reactive ion etching (RIE) and the device outline was dry etched through the top and bottom a-SiC layers. A final layer of polyimide was spin-coated over the top, pad/site openings were dry-etched through the polyimide to the metal by RIE, sputtered iridium oxide film (SIROF) electrode sites were patterned, and the arrays were singulated by dry-etching through the full polyimide thickness outside the a-SiC extent. The completed arrays were removed from the carrier substrate. Sample electrode arrays with and without the integrated a-SiC barrier were subjected to accelerated soak testing in an inorganic interstitial fluid (model-ISF). The performance of the SIROF electrodes on arrays with a-SiC was electrochemically evaluated.
A set of microfabrication processes was successfully engineered to integrate an a-SiC barrier around the signal conductors in a polyimide-based electrode array microfabrication process. The resulting arrays were found to withstand soaking in model-ISF at 87oC for 20 weeks within which time the arrays without a-SiC failed. The in vitro characterization of the SIROF electrodes demonstrated that the performance compared favorably with results previously reported for electrode arrays without a-SiC.
A means of fabricating a flexible polyimide-based electrode array with an a-SiC barrier has been developed. The technology was shown to significantly increase the life expectancy of the polyimide-based electrode arrays while maintaining excellent SIROF electrode performance. This microfabrication technology may provide the basis for future in vivo components of the Boston retinal prosthesis.
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