Ionising radiation effects in a soft X-ray CMOS image sensor

CIS221-X is a prototype monolithic CMOS image sensor, optimised for soft X-ray astronomy and developed for the proposed ESA THESEUS mission. A significant advantage of CMOS technology is its resistance to radiation damage. To assess this resistance, four backside-illuminated CIS221-X detectors have been irradiated up to a total ionising dose of 113 krad at the ESA ESTEC 60Co facility. Using unirradiated readout electronics, the performance of each sensor has been measured before and after irradiation. The gain, readout noise and dark current are shown to increase, while the image lag remains unchanged. These measurements are compared to that of similar CMOS image sensors and a possible physical explanation is provided for each result.