Fabrication and Characterization of a Parylene-Based Three-Dimensional Microelectrode Array for Use in Retinal Prosthesis

Abstract

A novel Parylene-based shape-transferring technique was developed to fabricate 3-D microelectrodes, which fulfilled the requirements of the high-density microelectrode array (MEA) used in retinal prosthesis. A process combining anisotropic and isotropic etching was utilized to form the 3-D silicon-tip array whose shape was transferred to the Parylene C film as a flexible and biocompatible substrate. Platinum was chosen as the electrode material owing to its high charge delivery capacity and chemical inertness in the physiological environment. An aluminum-photoresist dual-layer lift-off process was employed for platinum patterning on the substrate with high tips. To avoid the cracking problem existing in the platinum-Parylene C structure, a gold intermediate layer was introduced to retard the tendency. To test the superiority of the present 3-D flexible MEA compared with the planar one, electrical properties of MEAs were characterized both <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vitro</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vivo</i> . The experimental results showed that the impedance of the 3-D electrode was about 72.7% of the planar one at 1 kHz with the same footprint <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vitro</i> , and 71.5% <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vivo</i> . The preliminary surgical experiment validated the feasibility of the 3-D MEA in retinal prosthesis.