An Analytical Model of Dynamic Charge Transfer Process for CMOS Image Sensors

An analytical model is proposed to accurately describe the dynamic charge transfer process between the pinned photodiode (PPD) and floating diffusion (FD) node in CMOS image sensors (CISs). Two charge motion mechanisms, including self-induced drift and thermionic emission, are discussed in the proposed model. The transient charge transfer behavior is analyzed in different exposure conditions. The parameters such as PPD capacitance, PPD potential, and potential barrier are involved in describing the charge transfer process. The model has been verified by TCAD simulation and the test devices were fabricated with a $0.11\mu $ m CIS process. The proposed charge transfer model provides convenience for optimizing the charge transfer efficiency of CISs.