Annealing Effects on Radiation Hardened CMOS Image Sensors Exposed to Ultra High Total Ionizing Doses

Capabilities of rad-hard electronics are often degraded by post-irradiation annealing, whose effects need to be considered in designing complex systems, such as CMOS image sensors (CISs). In particular, the commonly accepted behavior of annealing cannot be systematically assumed, because reverse annealing does not necessarily come from the degradation of the defects, but could be the result of defects annealing non-uniformities. This article provides an extensive study of the dark current and pixel readout electronic behavior of CISs during irradiation and annealing, in order to provide some insights on these annealing non-uniformities. The isochronal annealing performed up to 300 °C demonstrates that, up until a certain temperature, reverse annealing is almost always present, but the 300 °C annealing always heals the system very efficiently. When performed on specially designed gated pixels for ultrahigh dose applications, adding a N+ drain further mitigates the radiation effects along with the reverse annealing. This proves the efficiency of these rad-hard designs and calls for further research in this radiation-hardening direction.