Testing of thin-film electrode arrays for cochlear implants of the future

The Nucleus cochlear implant has been shown to give substantial communication benefit to the severe to profoundly deaf. Future cochlear implants will incorporate an advanced multi-channel electrode array, which will enable better sound-coding strategies to be implemented. This new electrode array will be fabricated using state-of-the-art micromachining technology. Any long-term implanted device such as a cochlear implant must undergo rigorous testing to ensure biological safety. In this paper four tests for the micromachined array are discussed. The tests are based on electrochemical methods, and include open circuit potential, galvanostatic biphasic pulse, 4-electrode shorting tests, and electrochemical impedance spectroscopy. This paper demonstrates that these test techniques arc effective and informative in the development of thin-film electrode arrays. They can be used to verify the fabrication steps, electrode quality, and the suitability for the biological environment.