Design consideration of p-well structure for solid-state image sensors

The p-well structure has been widely used in solid-state image sensors to suppress blooming and smear. This structure, however, suffers from saturation-level shading, flicker, and saturation-level fixed pattern noise. This work clarifies that the p-well potential sway, due to transfer pulse feeding, brings about the shading and the flicker, and the impurity fluctuation in the silicon substrate causes the saturation-level fixed pattern noise. To eliminate the problems, new structures and new driving modes are proposed. As a result, the shading is reduced to a practically negligible level, and the flicker and the fixed pattern noise are completely suppressed.