Design and characterization of ionizing radiation-tolerant CMOS APS image sensors up to 30 Mrd (Si) total dose

An ionizing radiation-tolerant CMOS active pixel sensor (APS) image sensor test chip was designed employing the physical design techniques of enclosed geometry and P-channel guard rings. The test chip was fabricated in a standard 0.35-mum CMOS process that has a gate-oxide thickness of 7.0 nm. It was irradiated by a gamma-ray source up to a total ionizing radiation dose level of approximately 30 Mrd (Si) and was still functional. The most pronounced effect was the increase of dark current, which was linear with total dose level. The rate of dark current increase was about 1 to 2 pA/cm(2)/Krd (Si), depending on the design of the pixel. The results demonstrate that CMOS APS image sensors can be designed to be ionizing radiation tolerant to total dose levels up to 30 Mrd (Si). The fabrication process is standard CMOS, yielding a significant cost advantage over specialized radiation hard processes.