We present a 32-channel carbon fiber monofilament-based intracortical neural recording array fabricated through a combination of bulk silicon microfabrication processing and microassembly. This device represents the first truly two-dimensional carbon fiber neural recording array. The five-micron diameter fibers are spaced at a pitch of 38 microns, four times denser than the state of the art one-dimensional arrays. The fine diameter of the carbon fiber microwires affords both minimal cross-section and nearly three orders of magnitude greater lateral compliance than standard tungsten microwires. Both of these serve to minimize the adverse biological response to implanted devices, particularly compared to conventional implantable microelectrodes. The electrode pitch, in turn, has the potential to enable localization of individual units by detection at multiple adjacent sites, something traditionally the domain of polytrodes. The density, channel count, and size scale of this array are enabled by a microfabricated silicon substrate and a out-of-plane microassembly technique in which individual fibers are inserted through metallized and isotropically conductive adhesive-filled holes in the oxide-passivated silicon substrate. Insertion is eased and the fibers aligned to within five milliradians using an array of microfabricated funnels. The device is insulated in parylene for biocompatibility and electrical isolation, and the recording sites are electroplated with PEDOT:PSS to an impedance on the order of tens of kiloohms at 1 kHz. Further, this fabrication technique is scalable to a larger number of electrodes and allows for the potential future integration of microelectronics.
Project end date: 05/17/18