Implantable Subdural Electrode Arrays for Neural Recordings Based on MEMS Technologies

We present implantable subdural electrode arrays (ISEA) for neural recordings based on MEMS technologies. The electrode array is fabricated on a thin polyimide substrate and then encapsulated with biomedical-grade polydimethylsiloxane (PDMS). Then laser ablating with a CO₂ laser is applied to expose the electrode sites. Prototypes of 4times4 gold electrode arrays are fabricated with an exposed electrode diameter of 2.3 mm and electrode pitches of 5.0 mm. The conductor paths are 200-mum-wide. After package, the total array area is approximately 40 mm by 55 mm. To verify the functionality of the subdural electrodes, the electrochemical impedance spectroscopy is measured. At 1 kHz, the electrode impedances vary between 1.5 kOmega and 3.5 kOmega, and the phases between -85deg and -70deg. Meanwhile, the electrical resistance of the conductor paths is also evaluated under mechanical strain, which shows that the electrical resistance increases approximately linearly with the applied mechanical strain until the polyimide layer ruptures at ~10%. All the characteristics above will permit implanting the subdural electrode array to sense ECoG (electrocorticogram) for epilepsy diagnosis and so on.