Radiation Effects in Pinned Photodiode CMOS Image Sensors: Variation of Photodiode Implant Dose

This paper presents the effect of the photodiode implant dose on the radiation degradation of pinned photodiode (PPD) CMOS image sensors. Several custom image sensors with similar structures are manufactured using five different photodiode implant doses. Each image sensor comprises nine $32 \times 32$ pixel arrays with nine different pixel layouts. After testing the effect of the photodiode implant dose and the pixel layout on the key performances of the image sensors, they are irradiated using 50-MeV protons at ionizing doses from 10 to 100 krad. By comparing the radiation-induced performance degradation depending on the pixel layout and the implant dose, some insights can be given about the physical mechanisms responsible for the degradation and the location of the degradation sources within the pixel. Eventually, we conclude about how the photodiode implant dose should be tweaked to improve the radiation tolerance, depending on which performance criterion has to be optimized in priority.