High-yield benzocyclobutene(BCB) based neural implants for simultaneous intra- and extracortical recording in rats

A unique structure for chronically implantable cortical electrodes based on benzocyclobutene (BCB) biopolymer was designed to perform intracortical and extracortical neural recording simultaneously in basic neuroscience research using animal models. It was fabricated on silicon wafer using standard planar CMOS surface microfabrication technique. Dry-etchable BCB was used to insulate the electrode and provide flexibility for micro-motion compliance between brain tissue and skull. This electrode is also designed to ease the handling and implantation during the surgery and to integrate buffer circuits to improve the signal-to-noise ratio. The reliable fabrication process was developed to improve the electrode yield and performance. A 15 microm thick tungsten layer was sandwiched in the electrode tip to improve the stiffness for easy insertion during the surgery. The fabricated electrodes have two intra-cortical recording sites (20 x 20 microm) in the tip penetrating into the cortex and two epidural recording sites (80 x 80 microm) on each side wing, providing a 6 channel system. One via (40 x 40 microm) was also incorporated in the tip to balance the tip and provide the bio-seeding to improve the implants and neural tissue interaction. The acute surgical testing suggests that this electrode structure can penetrate the pia into the cortical tissue without damaging the electrode.