Study of CMOS APS responsivity enhancement: Ring-shaped photodiode

In this brief, the possibilities of complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS) spectral response improvement are discussed. Thorough submicrometer 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 and verified analytically. The functional dependence of the pixel response on the ring opening size was discovered and formulated for various wavelengths illumination. We show that the photodiodes with a 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, hence, proving that specific photodiode designs enable to selectively improve pixel color sensitivity.