Graeme Clark Collection

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Start date: 2000 × End date: 2009 × Type: Conference Paper × Subject: electrochemical impedance spectroscopy (EIS) ×

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    A prototype micro-machined thin-film electrode array for cochlear implants
    Parker, J. R. ; Duan, Y. Y. ; Patrick, J. ; Harrison, H. B. ; Reinhold, O. ; Clark, Graeme M. ( 2001)
    Development of a micromachined electrode array for cochlear implant application is presented. The device is constructed from a silicon substrate with sputtered platinum electrodes and connection tracks. Electrochemical impedance spectroscopy (EIS) is used to study the properties of the electrode, and to identify potential problems caused by the micromachining process and materials. A variety of insulators are studied and a two-part epoxy is identified as an adequate insulator for operation under harsh electrochemical testing conditions. The semiconducting silicon substrate is found to contribute to the total impedance of the device at high frequencies due to the thin insulating oxide between the substrate and conducting tracks. This is a potential problem for micromachined electrodes operating under high frequencies or using square stimulating pulses. The charge-delivery properties are studied using electrochemical impedance spectroscopy. It is found that platinum sputtered under particular conditions results in excellent surface conditions for optimum charge-delivery.
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    Potential applications of a small and high surface area platinum electrode as an implanted impedance bio-sensor or recording electrode.
    Duan, Yvonne Y. ; Millard, Rodney E. ; Tykocinski, Michael. ; Lui, Xugang ; Clark, Graeme M. ; COWAN, ROBERT ( 2001)
    A small Platinum (Pt) electrode (geometric area: -0.43 mm2) was treated in an electrochemical etching process, to produce a highly porous columnar thin layer (-600 nm) on the surface of the electrode. The modified Pt electrode (Pt-p) showed similar electrical properties to a platinum-black electrode but with high mechanical integrity. Previous studies of chronic stimulation had also shown good biocompatibility and surface stability over several months implantation. This paper discusses the potential applications of the modified electrode as an implanted bio-sensor: (1) as a recording electrode compared to an untreated Pt electrode. (2) as a probe in detecting electrical characteristics of living biological material adjacent to the electrode in vivo, which may correlate to inflammation or trauma repair. Results of electrochemical impedance spectroscopy (BIS) revealed much lower electrode interface polarisation impedance, reduced overall electrode impedance, and a largely constant impedance above 100 Hz for the Pt-p electrode compared with untreated Pt electrodes. This provides a platform for recording biological events with low noise interference. Results of A.C. impedance spectroscopy of the high surface area electrode only reflect changes in the surrounding biological environment in the frequency range (1 kHz to 100kHz), interference from electrode polarisation impedance can be neglected. The results imply that the surface-modified electrode is a good candidate for application to implantable biosensors for detecting bio-electric events. The modification procedure and its high surface area concept could have application to a smart MEMS device or microelectrode.