Backside illuminated pixel structure is proposed and evaluated as the building block for the image sensor being used as epiretinal prosthesis implant. The image sensor pixel is designed with the parameters of 90nm technology node of standard CMOS (Complementary Metal Oxide Semiconductor) process. The image sensor is consisted of a p-sub/n-well structure as the photosensitive area with the pixel pitch of 20μm. The maximum fill factor is observed due to separation of photosensitive area with the readout transistor surface in backside illumination technology. 90% quantum efficiency at 600nm wavelength and the dark current of 74.6nA/cm2 at room temperature is achieved for the optimized pixel. The application of deep backside Deep Trench Isolation (DTI), with high depth n-well doping profiles, results in a significant reduction of crosstalk (5.6% total crosstalk). 
Design and optimization of backside illuminated image sensor for epiretinal implants