In-pixel buried-channel source follower in CMOS image sensors exposed to X-ray radiation

This paper presents a CMOS image sensor (CIS) with pinned-photodiode 5T active pixels which use an in-pixel buried channel source follower (BSF) with an optimized row selector (RS). According to our previous work, using in-pixel BSFs with optimized RS can achieve significant pixel dark random noise reduction, i.e. 50% reduction, specially for random telegraph signal (RTS) noise, and an increase of the pixel output swing and dynamic range. With significant dark random noise reduction, in order to evaluate the performance for perspective space or medical imaging application, this proposed pixel structure using 0.18μm CMOS image sensor process is also further characterized under X-ray radiation. The results show that X-ray radiation induces additional acceptor-like interface traps which will increase dark random noise of the BSF pixels, to make BSF pixels less sensitive to radiation exposure, further optimization is necessary.