A study of radiation damage and heat annealing effect on the irradiated 3T active pixel sensor

The trend of x-ray image sensor has evolved from an amorphous silicon sensor to a crystal silicon sensor. A crystal silicon x-ray sensor, the x-ray CIS (CMOS Image Sensor), embodies three transistors: a Reset Transistor, a Source Follower and a Select Transistor, and a photodiode. They are highly sensitive to radiation exposure and proven to dramatically decrease quality of imaging device when frequency of exposure to radiation increases. The most well-known effect of the x-ray CIS due to the radiation damage are increments in the reset voltage and dark current. These effects cause the quality of image to degrade. To overcome these problems, many sensor recovery methods are studied. Annealing is the best method among many other methods. For the assembled sensor, the heat annealing is most suitable. In this study, a pixel array of the x-ray CIS was made from 1 × 11 pixels and this pixel array was exposed to a high radiation dose. From the irradiated pixel data, we determined the radiation damage of pixels. To recover the sensor for performance improvement, we annealed the irradiated sensor at high temperature.