Total ionizing dose effects on 4-transistor CMOS image sensor pixels

This work presents a study on the degradation mechanism of 4T CMOS Image Sensors (CIS) induced by X-Rays irradiation. The degradation is mainly demonstrated by measurements of increased dark signal and dark random noise. The radiation affects the sensor´s behavior differently for different reset voltages and transfer gate control, which is evaluated in detail. The basic failure mechanism is presented and it shows that the radiation induced increase of random telegraph signal noise and dark random noise is mostly originated from the Si-SiO₂ interface trap generation. Meanwhile, the charge trapping in the shallow trench isolation oxide (STI) is responsible for the post-irradiation dark signal increase as well. It is also illustrated that the post-irradiation pinned photodiode (PPD) and the transfer gate will obviously contribute to the sensor degradation as a post-irradiation dark signal and noise source.