CMOS 256-Pixel/480-Pixel Photovoltaic-Powered Subretinal Prosthetic Chips With Wide Image Dynamic Range and Bi/Four-Directional Sharing Electrodes and Their Ex Vivo Experimental Validations With Mice

Abstract

CMOS photovoltaic-powered 256-pixel/480-pixel implantable chips with a wide image dynamic range and shared electrodes are proposed and fabricated in CIS technology for subretinal prostheses. The infra-red (IR) light is incident only on photovoltaic cells of the chip whereas the visible light is mainly incident on pixels. The proposed adaptive background cancellation circuit (ABCC) is adopted to increase the image dynamic range so that the subretinal chips can adapt for different surrounding illuminances. A two-dimensional equivalent electrode model for electric crosstalk simulation is proposed to analyze the crosstalk charges and enable the stimulation pattern design with minimum crosstalk for both chips. Moreover, the bi-directional sharing electrodes (BDSEs) are used in the 256-pixel chip to increase electrode size under the same chip area and boost the stimulation charges to 11.4 nC. The four-directional sharing electrodes (FDSEs) are used to share the electrodes in both vertical and horizontal directions and achieve 480 pixels with nearly the same electrode size under the same pixel array area. The maximum stimulation charge is 9.8 nC. The dynamic range of image light is increased to 31.65 dB (24.9 dB) in the fabricated 256-pixel (480-pixel) chip. The functions of the chip have been successfully validated by both electrical measurement and ex vivo patch clamp experiments with the retinas of mice.