Design and Fabrication of a Multi-electrode Array for Spinal Cord Epidural Stimulation

A detailed design, fabrication, characterization and test of a flexible multi-site platinum/polyimide based electrode array for electrical epidural stimulation in spinal cord prosthesis is described in this paper. Carefully designed 8.4-thick structure fabrication flow achieves an electrode surface modification with 3.8 times enhanced effective surface area without extra process needed. Measured impedance and phase of two type of electrodes are 2.35 +/- 0.21 K Omega and 2.10 +/- 0.11 K Omega, -34.25 +/- 8.07 degrees and -27.71 +/- 8.27 degrees at 1K Hz, respectively. The fabricated arrays were then in-vitro tested by a multichannel neural stimulation system in physiological saline to validate the capability for electrical stimulation. The measured channel isolation on adjacent electrode is about -34dB. Randles cell model was used to investigate the charging waveforms, the model parameters were then extracted by various methods. The measured charge transfer resistance, double layer capacitance, and solution resistance are 1.9 K Omega, 220 nF and 15 K Omega, respectively. The results show that the fabricated array is applicable for electrical stimulation with well characterized parameters. Combined with a multichannel stimulator, this system provides a full solution for versatile neural stimulation applications.