A Nanowire FET Switch Integrated Microelectrode for High-Resolution Retinal Prosthetic System

Abstract

Retinal degenerative diseases result in a progressive degeneration of photoreceptors in the retina and eventually lead to complete blindness. While, pharmaceutical treatments and gene therapy may help maintain vision in the early stages of degeneration, survival of the inner nuclear and retinal ganglion layers support the approach to partially restore vision by electrical stimulation of surviving neurons using neural prostheses devices. However, tasks that require a fine resolution of visual information such as facial recognition and reading cannot be achieved, due to the limited number of microelectrode array caused by the wiring complexity. In this dissertation, novel silicon nanowires FET switch on a flexible substrate to implement a high-resolution microelectrode array for retinal prosthesis is presented. The silicon nanowire FET switch allows choosing active microelectrode for electrical stimulation of retina by selecting a specific row and column. The proposed microelectrode array has 32 × 32 pixels with unit pixel size of 100 μm × 100 μm. Each unit pixel consists of a stimulation electrode, a ground electrode, a nanowire FET switch, a data line, and a scan line. The data line and scan line, which is connected with outer pad, chooses a specific nanowire FET switch to activate microelectrode for electrical stimulation. The electrical characteristics of silicon nanowire FET switch are measured to evaluate the device performance. After fabrication the silicon nanowire FET switch integrated microelectrode array, experiment under phosphate buffered saline (PBS) solution is performed to evaluate the device characteristics. The threshold voltage, current on/off ratio, and on-resistance of the fabricated silicon nanowire FET switch is measured to be - 0.4 V, 1 × 10^7, and 43 kΩ at gate voltage of - 5V, respectively. The maximum allowable current injection limit of the fabricated silicon nanowire FET switch integrated microelectrode is measured as 48 μA at pulse duration of 1 ms. The presented performance evaluation results show that the proposed nanowire FET based microelectrode can be used for the implementation of high-resolution retinal prosthetic system.