ABSTRACT Iridium oxide (IrOx) has attracted much attention for neural interface applications due to its ability to transfer between ionic and electronic current and to resist corrosion. The physical, mechanical, chemical, electrical and optical properties of thin films depend on the method and parameters used to deposit the films. In this report, the surface morphology, impedance and charge capacity of activated iridium oxide film (AIROF) and sputtered iridium oxide film (SIROF) were investigated in vitro and compared. The Utah Electrode Array (UEA) having similar electrode area and shape were employed in this study. The electrode coated with AIROF and SIROF were characterized by scanning electron microcopy, cyclic voltammetry, electrochemical impedance spectroscopy and potential transient measurements to measure charge injection capacity (CIC). SIROF and AIROF selectively deposited on electrode tip had dendrite and granular microstructure, respectively. The CIC of unbiased SIROF and AIROF was found to be 2 and 1 mC/cm2, respectively, which is comparable to other published values. The average impedance, at a frequency of 1 kHz was ~65 and ~7 kΩ for the AIROF and SIROF, respectively. Low impedance and high CIC makes SIROF highly recommended stimulation and recording material.
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S. Negi, R. Bhandari and F. Solzbacher, "Morphology and Electrochemical Properties of Activated and Sputtered Iridium Oxide Films for Functional Electrostimulation," Journal of Sensor Technology, Vol. 2 No. 3, 2012, pp. 138-147. doi: 10.4236/jst.2012.23020.
 F. T. Hambrecht and J. Reswick, “Functional Electrical Stimulation: Application in Neural Prostheses,” Marcel Dekker, New York, 1977.
 R. A. Normann, “Technology Insight: Future Neuroprosthetic Therapies for Disorders of the Nervous System,” Nature Clinical Practice Neurology, Vol. 3, No. 8, 2007, pp. 444-452. doi:10.1038/ncpneuro0556
 J. D. Klein, S. L. Clauson and S. F. Cogan, “The Influence of Substrate Bias on the Morphology and Charge Capacity of RF-Sputtered Iridium Oxide Films,” Journal of Materials Research, Vol. 4, No. 6, 1989, 1505-1510.
 J. D. Klein, S. L. Clauson and S. F. Cogan, “Morphology and Charge Capacity of Sputtered Iridium Oxide Films,” Journal of Vacuum Science & Technology A, Vol. 7, No. 5 1989, pp. 3043-3047. doi:10.1116/1.576313
 J. A. Thornton, “Influence of Apparatus Geometry and Deposition Conditions on the Structure and Topography of Thick Sputtered Coatings,” Journal of Vacuum Science & Technology A, Vol. 11, No. 4, 1974, pp. 666-671.
 H.-J. Cho, H. Horii, C. S. Hwang, J.-W. Kim, C. S. Kang, et al., “Preparation and Characterization of Iridium Oxide Thin Films Grown by DC Reactive Sputtering,” Journal of Applied Physics, Vol. 36, 1997, pp. 1722-1727.
 C. U. Pinnow, I. Kasko, N. Nagel, S. Poppa, et al., “Influence of Deposition Conditions on Ir/IrO2 Oxygen Barrier Effectiveness,” Journal of Applied Physics, Vol. 91, No. 12, 2002, pp. 9591-9597.doi:10.1063/1.1471574
 E. Slavcheva, R. Vitushinsky, W. Mokwa and U. Schnakenberg, “Sputtered Iridium Oxide Films as Charge Injection Materials for Functional Electrostimulation,” Journal of the Electrochemical Society, Vol. 151, No. 7, 2004, pp. 226-237. doi:10.1149/1.1747881
 S. Negi, R. Bhandari, L. Rieth and F. Solzbacher, “Effect of Sputtering Pressure on Pulse-DC Sputtered Iridium Oxide Films,” Sensors and Actuators: B Chemical, Vol. 137, No. 1, 2009, pp. 370-378.
 X. Beebe and T. L. Rose, “Charge Injection Limits of Activated Iridium Oxide Electrodes with 0.2 msec Pulses in Bicarbonate Buffered Saline,” IEEE Transactions on Biomedical Engineering, Vol. 35, No. 6, 1988, pp. 494-495. doi:10.1109/10.2122
 L. S. Robblee, J. L. Lefko and S. B. Brummer, “Activated Iridium: An Electrode Suitable for Reversible Charge Injection in Saline Solution,” Journal of the Electrochemical Society, Vol. 130, No. 3, 1983, pp. 731-733.
 P. F. Johnson and L.L. Hench, “An in Vitro Analysis of Metal Electrodes for Use in the Neural Environment,” Brain Behavior and Evolution, Vol. 14, No. 1-2, 1977, pp. 23-45. doi:10.1159/000124612
 R. Kotz, H. Neff and S. Stucki, “Anodic Iridium Oxide Films,” Journal of the Electrochemical Society, Vol. 131, 1984, pp. 72-77. doi:10.1149/1.2115548
 K. S. Kang and J. L. Shay, “Blue Sputtered Iridium Oxide Films (Blue SIROF’s),” Journal of the Electrochemical Society, Vol. 130, 1983, pp. 766-769.
 J. D. E. McIntyre, W. F. Peck and S. Nakahara, “Oxidation State Changes and Structure of Electrochromic Iridium Oxide Films,” Journal of the Electrochemical Society, Vol. 127, 1980, pp. 1264-1268. doi:10.1149/1.2129868
 P. C. Liao, W. S. Ho, Y. S. Huang and K. K. Tiong, “Characterization of Sputtered Iridium Dioxide Thin Films,” Journal of Materials Research, Vol. 13, No. 5, 1998, pp. 1318-1326. doi:10.1557/JMR.1998.0187
 R. Bhandari, S. Negi and F. Solzbacher, “Wafer Scale Fabrication of Penetrating Neural Electrode Arrays,” Biomedical Microdevices, Vol. 12, No. 5, 2010, pp. 797-807.
 R. Bhandari, S. Negi, L. Rieth, R. A. Normann, et al., “A Wafer Scale Etching Technique for High Aspect Ratio Implantable MEMS Structures,” Sensors and Actuators A: Physical, Vol. 162, No. 1, 2010, pp. 130-136.
 S. Negi, R. Bhandari, L. Rieth, F. Solzbacher, “In Vitro Comparison of Sputtered Iridium Oxide and Platinum Coated Neural Implantable Microelectrode Arrays,” Biomedical Materials, Vol. 5, No. 1, 2010, Article ID: 015007.
 A. Norlin, J. Pan and C. Leygraf, “Investigation of Interfacial Capacitance of Pt, Ti and TiN Coated Electrodes by Electrochemical Impedance Spectroscopy,” Biomolecular Engineering, Vol. 19, No. 2-6, 2002, pp. 67-71.
 B. He, “Neural Engineering: Interfacing Neural Tissue with Microsystems Bioelectric Engineering,” Kluwer Academic/Plenum Publishers, New York, 2005.
 S. F. Cogan, “Neural Stimulation and Recording Electrodes,” Annual Review of Biomedical Engineering, Vol. 10, 2008, pp. 275-309.
 S. F. Cogan, P. R. Troyk, J. Ehrlich and T. D. Plante, “In Vitro Comparison of the Charge Injection Limits of Activated Iridium Oxide (AIROF) and Platinum-Iridium Microelectrodes,” IEEE Transactions on Biomedical Engineering, Vol. 52, No. 9, 2005, pp. 1612-1614.
 D. B. McCreery, W. F. Agnew, T. G. H. Yuen and L. Bullara, “Charge Density and Charge per Phase as Cofactors in Neural Injury Induced by Electrical Stimulation,” IEEE Transactions on Biomedical Engineering, Vol. 37, No. 10, 1990, pp. 996-1101. doi:10.1109/10.102812
 S. Negi, R. Bhandari, L. Rieth, R. V. Wagenen and F. Solzbacher, “Neural Electrode Degradation from Continuous Electrical Stimulation: Comparison of Sputtered and Activated Iridium Oxide,” Journal of Neuroscience Methods, Vol. 186, No. 1, 2010, pp. 8-17.