Gamma Radiation Damage Study of 0.18 μm Process CMOS Image Sensors

A 0.18 mu m process CMOS image sensor has recently been developed by e2v technologies plc. with a 0.5 megapixel imaging area consisting of 6 x 6 mu m 5T pixels. The sensor is able to provide high performance in a diverse range of applications including machine vision and medical imaging, offering good low-light performance at a video rate of up to 60 fps. The CMOS sensor has desirable characteristics which make it appealing for a number of space applications. Following on from previous tests of the radiation hardness of the image sensors to proton radiation, in which the increase in dark-current and appearance of bright and RTS pixels was quantified, the sensors have now been subjected to a dose of gamma radiation. Knowledge of the performance after irradiation is important to judge suitability for space applications and radiation sensitive medical imaging applications. This knowledge will also enable image correction to mitigate the effects and allow for future CMOS devices to be designed to improve upon the findings in this paper. One device was irradiated to destruction after 120 krad(Si) while biased, and four other devices were irradiated between 5 and 20 krad( Si) while biased. This paper explores the resulting radiation damage effects on the CMOS image sensor such as increased dark current, and a central brightening effect, and discusses the implications for use of the sensor in space applications.