The effect of hot carriers on the operation of CMOS active pixel sensors

Abstract

Excess minority carriers induced by hot carriers in source follower transistors in active pixel sensors are experimentally observed using sensor arrays fabricated with a standard 0.35-/spl mu/m CMOS process. The number of carriers absorbed by photodiodes depends on bias conditions of the transistors and consequently becomes optical-signal dependent. A cascoded 4-T active pixel sensor is more sensitive to this effect due to its small sensing capacitance. Temperature varying experiments are performed to confirm this mechanism. The spatial distribution of the excess carriers is quantified to be within /spl sim/30 /spl mu/m around the source follower transistors. Suggestions on pixel design are provided.