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Evaluation of Charge Injection Properties of Thin Film Redox Materials for use as Neural Stimulation Electrodes

Published online by Cambridge University Press:  26 February 2011

Ellen M. Kelliher
Affiliation:
EIC Laboratories, Inc., 111 Downey Street, Norwood, MA 02062
Timothy L. Rose
Affiliation:
EIC Laboratories, Inc., 111 Downey Street, Norwood, MA 02062
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Abstract

The charge injection limits of a variety of thin film redox materials considered for use as neural stimulation electrodes were evaluated under standardized conditions. Materials tested included the oxides of Ni, Ir, Rh, Ru, and Mn as well as conductive polypyrrole films. Electrodes with geometric areas of, ∼10–4 cm2 were tested in bicarbonate buffered saline of pH 7.3. An electrochemically “safe” potential window was determined for each material by cyclic voltammetry. Charge injection capabilities within that window are evaluated with constant current 0.2 msec pulses. Pulse modes include anodic first and cathodic first biphasic pulses and monophasic cathodal pulses applied to electrodes held at an anodic bias. Pulsing from the anodic bias increased the charge limits for all the materials, but the most dramatic improvement was for Rh oxide. The highest charge injection values were obtained with oxides of iridium and rhodium and were of comparable value for the anodic bias mode of pulsing. Where the effect of film thickness was examined, the charge injection limit leveled off at 2–4 mC/cm2 geometric as the film thickness increased.

Type
Research Article
Copyright
Copyright © Materials Research Society 1988

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