A novel structure for chronically implantable cortical electrodes using new Benzocyclobutene (BCB) bio-polymer was devised, which provides both flexibility for micro-motion compliance between brain tissues and skull and stiffness for better surgical handling. BCB is very attractive polymer for stable long-term implant function, because it has flexibility, biocompatibility, low moisture uptake (<0.2 wt%), and low dielectric constant (/spl sim/2.6). For easy operation during surgical insertion, a 5/spl sim/10/spl mu/m thick silicon backbone layer is attached to the desired region of the electrode to increase the stiffness. It is then followed by 1 mm of flexible part of the electrode without silicon backbone layer designed to absorb stress from any micro-motion between the brain tissue and the electrode. The fabricated implants have tri-shanks with 5 recording sites (20x20/spl mu/m) and 2 vias (40x40/spl mu/m) on each shank. BCB electrodes with 5/spl mu/m and 10/spl mu/m thick backbone silicon penetrated pia of rat brain without buckling.