Dynamic Model of FWC Dependent on the Energy-Level Distribution of Interface-State Traps in Pinned Photodiodes

Abstract

Full well capacity (FWC) modeling has been widely used to clarify the imaging characteristics of the pinned photodiode (PPD) in complementary metal-oxide-semiconductor (CMOS) image sensors. Until now, FWC modeling has considered only the effects of temperature, doping, and photon dependence on the FWC. However, the influence of the distribution of interface trap-state energy levels on the FWC is ignored. Therefore, this article proposes a dynamic FWC model that depends on the energy-level distribution of interface trap states in a PPD for the first time. By establishing a 2-D function for the reverse saturation current related to the trap-state density and trap energy level, an explicit 2-D expression is derived for the full well potential associated with trap-state density and trap energy level. According to the relationship between the full well potential and FWC, as well as the relationships among the trap-state density, trap energy level, and trap energy-level distribution, a dynamic model of the FWC is deduced that depends on the trap energy-level distribution. The consistency between results of TCAD simulations and our theoretical model shows that the FWC is not a single fixed value but a set of dynamic values that change with the distribution of trap energy levels.