Design and simulation of a radiation hardening pixel in the CIS detector used in high total ionizing dose damage environment

A radiation hardening pixel design of a CMOS image sensor (CIS) detector is presented. We try to improve the radiation hardening ability by suppressing the dark current increase induced by radiation damage. By adjusting the horizontal and longitudinal doping depths of the P-well injection layer around the STI, we found it can restrain the pinned photodiode (PPD) depletion layer from connecting the STI depletion layer under high total ionizing dose (TID) radiation. The simulation results show that the PPD depletion layer will connect with the STI depletion layer of a CMOS image sensor (CIS) detector with a conventional P-well injection layer around the STI when the total ionizing dose (TID) is larger than 30 krad(Si). By adjusting the horizontal and longitudinal doping depths of the P-well injection layer around the STI, the PPD depletion layer and the STI depletion layer still keep isolated when the TID is up to 2000 krad(Si). Thus, the dark current increase induced by TID damage will be suppressed. For example, when the TID is 100 krad(Si), the SRH recombination rate in PPD depletion region before optimization is 2.64×1014 cm-3s-1 while it is 6.06×1013 cm-3s-1 after optimization. This is because the optimization of the p-well injection layer at the edge of STI can keep the STI depletion region and the PPD depletion region isolated under high TID radiation. The SRH recombination rate decrease will decrease the dark current degradation.