Excimer laser deinsulation of Parylene-C on iridium for use in an activated iridium oxide film-coated Utah electrode array

Implantable microelectrodes provide a measure to electrically stimulate neurons in the brain and spinal cord and record their electrophysiological activity. A material with a high charge capacity such as activated or sputter-deposited iridium oxide film (AIROF or SIROF) is used as an interface. The Utah electrode array (UEA) uses SIROF for its interface material with neural tissue and oxygen plasma etching (OPE) with an aluminium foil mask to expose the active area, where the interface between the electrode and neural tissue is formed. However, deinsulation of Parylene-C using OPE has limitations, including the lack of uniformity in the exposed area and reproducibility. While the deinsulation of Parylene-C using an excimer laser is proven to be an alternative for overcoming the limitations, the iridium oxide (IrOx) suffers from fracture when high laser fluence (>1000 mJ/cm2) is used. Iridium (Ir), which has a much higher fracture resistance than IrOx, can be deposited before excimer laser deinsulation and then the exposed Ir film area can be activated by electrochemical treatment to acquire the AIROF. Characterisation of the laser-ablated Ir film and AIROF by surface analysis (X-ray photoelectron spectroscopy, scanning electron microscope, and atomic force microscope) and electrochemical analysis (electrochemical impedance spectroscopy, and cyclic voltammetry) shows that the damage on the Ir film induced by laser irradiation is significantly less than that on SIROF, and the AIROF has a high charge storage capacity. The results show the potential of the laser deinsulation technique for use in high performance AIROF-coated UEA fabrication.

[1]  J. A. Wolf,et al.  UV laser ablation of parylene films from gold substrates , 2011 .

[2]  D.J. Anderson,et al.  Batch fabricated thin-film electrodes for stimulation of the central auditory system , 1989, IEEE Transactions on Biomedical Engineering.

[3]  F. Solzbacher,et al.  In vitro comparison of sputtered iridium oxide and platinum-coated neural implantable microelectrode arrays , 2010, Biomedical materials.

[4]  Excimer-laser deinsulation of Parylene-C coated Utah electrode array tips , 2012 .

[5]  Stuart F Cogan,et al.  Over-pulsing degrades activated iridium oxide films used for intracortical neural stimulation , 2004, Journal of Neuroscience Methods.

[6]  Florian Solzbacher,et al.  Hybrid laser and reactive ion etching of Parylene-C for deinsulation of a Utah electrode array , 2012 .

[7]  Thomas Stieglitz,et al.  An Optically Powered Single-Channel Stimulation Implant as Test System for Chronic Biocompatibility and Biostability of Miniaturized Retinal Vision Prostheses , 2007, IEEE Transactions on Biomedical Engineering.

[8]  T. Lu,et al.  A Model for the Chemical Vapor Deposition of Poly(para-xylylene) (Parylene) Thin Films , 2002 .

[9]  Kewei Liu,et al.  KrF excimer laser micromachining of MEMS materials: characterization and applications , 2011 .

[10]  S. Gottesfeld,et al.  Electrochromism in Anodic Iridium Oxide Films II . pH Effects on Corrosion Stability and the Mechanism of Coloration and Bleaching , 1979 .

[11]  Rajmohan Bhandari,et al.  Effect of sputtering pressure on pulsed-DC sputtered iridium oxide films , 2009 .

[12]  Jon A. Mukand,et al.  Neuronal ensemble control of prosthetic devices by a human with tetraplegia , 2006, Nature.

[13]  K. Horch,et al.  A silicon-based, three-dimensional neural interface: manufacturing processes for an intracortical electrode array , 1991, IEEE Transactions on Biomedical Engineering.

[14]  Florian Solzbacher,et al.  Encapsulation of an Integrated Neural Interface Device With Parylene C , 2009, IEEE Transactions on Biomedical Engineering.

[15]  A. Wiȩckowski,et al.  X-ray photoelectron spectroscopy and electrochemical surface characterization of iridium(IV) oxide + ruthenium(IV) oxide electrodes , 1992 .

[16]  J. Brannon,et al.  Excimer laser etching of polyimide , 1985 .

[17]  김성준,et al.  Neural stimulation and recording electrode array and method of manufacturing the same , 2012 .

[18]  F Solzbacher,et al.  A Wafer-Scale Etching Technique for High Aspect Ratio Implantable MEMS Structures. , 2010, Sensors and actuators. A, Physical.

[19]  G. Beni,et al.  Electrochromism in anodic iridium oxide films , 1978 .

[20]  P. Pickup,et al.  A MODEL FOR ANODIC HYDROUS OXIDE GROWTH AT IRIDIUM , 1987 .

[21]  S. B. Brummer,et al.  Activated Ir: An Electrode Suitable for Reversible Charge Injection in Saline Solution , 1983 .

[22]  R. Normann,et al.  A Novel Method of Fabricating Convoluted Shaped Electrode Arrays for Neural and Retinal Prosthesis , 2007, TRANSDUCERS 2007 - 2007 International Solid-State Sensors, Actuators and Microsystems Conference.

[23]  T Stieglitz,et al.  Diffusion-Limited Deposition of Parylene C , 2011, Journal of Microelectromechanical Systems.

[24]  Richard A Normann,et al.  Technology Insight: future neuroprosthetic therapies for disorders of the nervous system , 2007, Nature Clinical Practice Neurology.

[25]  B. Conway,et al.  Modification of Apparent Electrocatalysis for Anodic Chlorine Evolution on Electrochemically Conditioned Oxide Films at Iridium Anodes , 1981 .

[26]  L L Hench,et al.  An in vitro analysis of metal electrodes for use in the neural environment. , 1977, Brain, behavior and evolution.

[27]  D. McCreery,et al.  Neural prostheses : fundamental studies , 1990 .

[28]  James Hammond Brannon,et al.  Ambient gas effects on debris formed during KrF laser ablation of polyimide , 1992 .

[29]  Rajmohan Bhandari,et al.  Neural electrode degradation from continuous electrical stimulation: Comparison of sputtered and activated iridium oxide , 2010, Journal of Neuroscience Methods.

[30]  G. Loeb,et al.  Parylene as a Chronically Stable, Reproducible Microelectrode Insulator , 1977, IEEE Transactions on Biomedical Engineering.