For decades, the recording and electrical stimulation of nerve cells employed in neural prostheses (mainly auditory and motor prosthetics) has significantly improved the lives of patients. However, only recently have several research groups had the incentive to develop a retinal prosthesis to restore vision for the millions of blind and partially sighted people who suffer from age-related macular degeneration (AMD) and retinitis pigmentosa (RP). A number of experiments have demonstrated that vision could be restored by communicating directly with retinal neurons. This can be achieved through an array of implanted microelectrodes, which supply electrical stimulation pulses at various locations on the retina.

However, current retinal implants provide just a few electrodes where...[ Read more ]

For decades, the recording and electrical stimulation of nerve cells employed in neural prostheses (mainly auditory and motor prosthetics) has significantly improved the lives of patients. However, only recently have several research groups had the incentive to develop a retinal prosthesis to restore vision for the millions of blind and partially sighted people who suffer from age-related macular degeneration (AMD) and retinitis pigmentosa (RP). A number of experiments have demonstrated that vision could be restored by communicating directly with retinal neurons. This can be achieved through an array of implanted microelectrodes, which supply electrical stimulation pulses at various locations on the retina.

However, current retinal implants provide just a few electrodes whereas at least several thousand of pixels are required for functional restoration of sight. As the area of the retina targeted for electrical stimulation is less than 4 mm by 4 mm, an increase in the number of electrodes necessitates a decrease in their size and spacing. Such decrease in size and spacing of electrodes presents multiple challenges that are addressed in this research.

This thesis is concerned with the development of a novel high-density carbon nanotube microelectrode array chip for use in an epiretinal prosthesis. Vertically aligned carbon nanotubes (VACNT) were synthesized by microwave plasma-enhanced chemical vapor deposition and thermal chemical vapor deposition and were characterized by electrochemical experiments such as cyclic voltammetry, impedance spectroscopy and potential transient measurements. Through-silicon vias (TSVs) were fabricated and partially filled with polycrystalline silicon to allow electrical connection from the electrodes to a stimulator microchip. In response to the demand for a higher resolution retinal prosthesis, we have developed a unique process to obtain a high-density electrode array by making the microelectrodes smaller in size and larger in number.