Electrical characteristics of 2D and 3D microelectrodes for high-resolution retinal prostheses

In order to provide high quality visual information to patients who have implanted retinal prosthetic devices, the number of microelectrode should be large. As the number of microelectrode is increased, the dimension of the microelectrode is decreased, which in turn results in the increased interface impedance of microelectrode and decreased dynamic range of injection current. In addition, the reduced maximum limit of injection current may not be sufficiently large to stimulate the ganglion cells in a retina. In order to improve the trade-off envelope between number of microelectrode and current injection limit, a 3D microelectrode structure can be used as an alternative. From the advancement of microfabrication technology, the fabrication of highly-accurate 3D structures with small dimensions is possible. This paper presents a first comprehensive electrical characterization of 2D and 3D microelectrodes for high-resolution retinal prostheses. Microelectrodes which differ in shapes and diameters are analyzed. Their interface impedances and charge injection limits are quantitatively analyzed. This research can be used to define requirements for further retinal prosthetic device research.