Ring-shaped N+/P-well photodiode: study of responsivity enhancement

In this work the possibilities of CMOS APS spectral response improvement is discussed. Thorough submicron scanning results obtained from various ring-shaped pixel photodiodes with different inner radius, implemented in a standard CMOS 0.35 μm technology, are compared with numerical computer simulations. The functional dependence of the pixel response on the ring opening size was discovered and formulated for various illumination wavelengths. We show that the photodiodes with small ring-opening exhibit better sensitivity in the blue spectrum range (420-460 nm). Comparison between the simulation and measurement results shows a good agreement and, therefore, involving specific photodiode enables improved pixel color selectivity design.