Flat spectral response of a CMOS photodiode using wedge structures in back-end SiO₂

CMOS photodiodes are used in many light sensing applications; however, the performance can be limited by oscillations in the spectral response caused by light interference from the back-end oxide. Gray-scale lithography has been used to fabricate wedge-like structures in the back-end oxide, which reduces the light interference and oscillations over the entire silicon sensitivity range. Dielectric filter stacks have been deposited on top of the structures, demonstrating an improved spectral response over photodiodes, with filters deposited directly on silicon. The present approach is suitable for mass production and fully compatible with CMOS.