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0926-CC06-04

Fabrication and Characterization of Flexible, Microfabricated Neural Electrode Arrays Made from Liquid Crystal Polymer and Polynorbornene Varun Vardhan Keesara1, Dominique M. Durand2, and Christian A. Zorman1 1 Electrical Engineering and Computer Science, Case Western Reserve University, 10900 Euclid Ave, Cleveland, Ohio, 44106 2 Biomedical Engineering, Case Western Reserve University, 10900 Euclid Ave, Cleveland, Ohio, 44106 ABSTRACT This paper reports the development of flexible, neural electrode arrays made from liquid crystal polymer (LCP) and polynorbornene (PNB). Each array consists of a single flexible, polymeric structure composed of an 8 mm-wide pad supporting eight Pt contacts connected to an ASIC mounting pad by a 5 cm-long, 2 mm-wide shaft carrying eight, 50 µm-wide Pt interconnect lines. The Pt conductors sit atop a 50 µm-thick base layer and are isolated from the environment except at the contacts by a capping layer of the same material as the base. In both cases, the devices were fabricated using conventional microfabrication techniques adapted for the particular polymeric material. In the case of LCP, the base structure was fabricated on 50 µm -thick sheets that were laminated and etched into the final structure. PNB is spin castable and photodefinable, which enabled conventional photolithographic patterning techniques to be employed in a straightforward manner. The PNB-based devices could readily be fabricated, however issues related to LCP etching necessitated the development of a multi-step etch process to form the vias. Electrodes made from both polymers could support loads typical of stimulation applications. A simple cell culture test suggests that AvatrelTM may be biocompatible. INTRODUCTION Microfabrication techniques are currently being developed for flexible polymeric substrates using materials that were initially developed for electronic packaging but are equally attractive candidates as structural components in micromachined devices. An emerging technology that is beginning to benefit from these developments is advanced neural electrode arrays for implantable, minimally invasive, neural prostheses. The leading materials in this area include polyimides [1], parylene [2], and liquid crystal polymers (LCP) [3]. Polyimides suffer from high moisture absorption rates, making them problematic for long-term implants. Parylene bests polyimide in terms of moisture absorption, but only by roughly 10X. LCP absorption rates are 50X lower than the best polyimide, but multilayered structures require lamination, making microfabrication much more challenging than either of the other two. This paper reports on our effort to advance the development of LCP and polynorbornene (PNB) for use as the principal material in flexible, neural electrode arrays. LCP has previously been used in neural electrode arrays; but only as a structural base supporting unprotected conductors [3] thus limiting its utility. To the best of our knowledge, PNB has not yet been used in such devices despite the fact that t