Fabrication of implantable polyimide based neural implants with flexible regions to accommodate micromovement

A unique structure for chronically implantable cortical electrodes using polyimide polymer was devised, which provides both flexibility between brain tissues and skull and stiffness for easy insertion. The fabricated implants are tri-shanks with 5 recording sites (20/spl times/20 /spl mu/m) and 2 vias per electrode of 40/spl times/40 /spl mu/m. Each recording site was connected to the external circuitry via a 15-channel connector, which is especially designed to facilitate processing of neural signals to the external circuitry. Measured impedance values are in /spl sim/2 Mohm at 1 KHz. For a 5 /spl mu/m thick silicon backbone electrode, the stiffness was improved 10 times larger than that of the electrode without silicon backbone layer. Stiff electrodes with 5 /spl mu/m and 10 /spl mu/m thick backbone silicon penetrated pia of rat without buckling.