Flexible PET/ITO electrode array for implantable biomedical applications

Flexible PET/ITO (PolyEthylene Terephthalate/ Indium Tin Oxide) implantable electrode array for spinal cord stimulation and retina prosthesis have been developed. The electrode array is fabricated on a thin PET/ITO substrate and encapsulated with insulating material, SU-8. The PET substrate made electrodes flexible so that they could shape to contoured tissues. A layer of gold on the stimulation sites served to reduce the electrode/tissue interface impedance. Prototypes of 1×8 and 3×8 electrode arrays are fabricated for monophasic and biphasic stimulation of spinal cord respectively. The exposed electrode dimensions are 3mm² for monophasic and 6mm² for biphasic stimulation with 100μm of interconnection paths. The prototype of 4×4 electrode arrays were also fabricated with the same process for retinal prosthesis with exposed electrode diameter of 125μm. To verify the functionality of the subdural electrodes, the electrochemical impedance spectroscopy was measured. The electrode/tissue impedance was 500Ω at 1KHz for 3mm² area.