| AVS 55th International Symposium & Exhibition | |
| BioMEMS Topical Conference | Tuesday Sessions |
| Session BM-TuP |
| Session: | BioMEMS |
| Presenter: | S. Negi, University of Utah |
| Authors: | S. Negi, University of Utah R. Bhandari, University of Utah L. Rieth, University of Utah R.A. Normann, University of Utah F. Solzbacher, University of Utah |
| Correspondent: | Click to Email |
To provide low impedance electrical connection between the neural electrode and the nerve, the electrodes are coated with conductive material like Iridium oxide (IrOx) due to its higher charge injection capacity and resistance to corrosion.1 In this report, IrOx is deposited by two methods; activation of iridium to form activated iridium oxide film (AIROF), and reactive sputtering to form sputtered iridium oxide film (SIROF) on similar shape and size neural electrodes. The AIROF and SIROF properties are studied and the results are compared. Utah Electrode Arrays (UEAs), were used for this study.2 To fabricate AIROF coated UEA, 99.8 % pure Ir was DC sputter deposited on to the UEA tips using an Ar pressure of 20 mTorr, and 5W power for 12 minutes to achieve 1000 Å thickness. The Ir electrodes were activated by cyclic voltammetry (CV), sweeping between -0.8 to +0.8 V versus Ag/AgCl in phosphate buffered saline (PBS) solution at the rate of 1 Hz. The SIROF films were deposited on the UEA tips by pulsed-DC reactive sputtering with 50%:50% ratio of Ar and O2 in the ambient, keeping the chamber pressure at 10 mTorr. Ar and O2 flow rates were both 100 sccm. The pulse frequency was at 100 kHz, the duty-cycle was 30 percent, and a power of 100 W was used to achieve thickness of 1000 Å after 20 minutes of deposition. Charge storage capacity for AIROF and SIROF coated UEAs was found to be 10 and 38 mC/cm2, respectively. The electrochemical impedance at 1 kHz was measured for AIROF and SIROF as a function of the exposed UEA tip. At 100 µm tip exposure, AIROF and SIROF impedance were 36 and 6 kΩ respectively, while, at 20 µm tip exposure the AIROF and SIROF impedance were 200 and 50 kΩ respectively. The results indicate that decreasing the tip exposures increases impedance exponentially. SIROF coated electrodes have lower impedance and, potentially, will offer higher neural selectivity without compromising on the electrode sensitivity. The higher charge storage capacity and lower impedance makes SIROF a promising material for stimulating and recording neural signals.
1 W. F. Agnew and D. B. McCreery (Eds), Neural Prostheses: Fundamental Studies, Prentice Hall Biophysics and Bioengineering series.
2 K. E. Jones, P. K. Campbell, and R. A. Normann, A glass/silicon composite intracortical electrode array, Ann. Biomed. Eng., vol. 20, no., pp 423-37, 1992.