A nanowire FET switch integrated with a microelectrode array for retinal prosthetic systems

In this paper, a novel retinal prosthetic system, combining nanowire field-effect transistor (FET) switches with microelectrodes is developed. In order to minimize the wiring complexity of high-resolution microelectrode arrays, silicon nanowire-FET switches are integrated with microelectrodes. Also, in order to fit the curvature of an eyeball, the silicon nanowire-FET is transferred to a flexible substrate. A microelectrode array with 32 × 32 pixels is fabricated, which has 1,024 microelectrodes. Using the FET switches in a 2-dimensional array-addressing configuration, 1,024 microelectrodes are addressed by only 64 lines (32 for scan and 32 for data), as compared to requiring 1,024 lines in the conventional one-to-one configuration. The threshold voltage, current on/off ratio, and on-resistance of the fabricated silicon nanowire FET switch are measured to be -0.4 V, 1 × 10⁷, and 43 KΩ at gate voltage of -5 V, respectively. The maximum allowable current injection limit of the silicon nanowire-FET switch integrated microelectrode is measured as 48 μA at pulse duration of 1 ms. The concept of FET switching of collocated retinal electrodes is completely novel, and highly scalable. The results have a high potential to realize high-resolution retinal prosthetic systems.