A design consideration on 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 readout pulse feeding, brings about the shading and the flicker. and the impurity striation in silicon substrate causes the saturation fixed pattern noise. To eliminate the problems, a new structure and a new driving mode are proposed. As a result, the shading and the fixed pattern noise were reduced to a practically negligible level, and the flicker was completely suppressed.