Pixel Simulation Of Total Ionizing Dose Effect On PPD CMOS Image Sensor

As a core component of the optical imaging system in spacecraft,the problem of total ionizing dose radiation damage suffered by CMOS image sensors in the space radiation environment is of concern,especially the total ionizing dose effect induced the performance degradation of the 4-transistor pinned photodiode(4T-PPD)CMOS image sensors.Computer simulation is an important means of improving the total ionizing dose radiation hardened technology of the electronic components.It not only reproduces the evolution of the internal sensitive parameters of the electronic components under the total ionizing dose irradiation,but also can effectively distinguish the sensitive regions of performance degradation induced the total ionizing dose effect.It is important for further research on the total ionizing dose effect of electronic components by computer simulation.In this paper,based on the present situation of the total ionizing dose effect of4T-PPD CMOS image sensor in our country,we carried out the simulation of total ionizing dose effect on the pixel unit of the 4T-PPD CMOS image sensor and radiation experiment by 60 Co ?-rays.The degradation of sensitive parameters and the change of sensitive regions after total ionizing dose irradiation were analyzed in4T-PPD CMOS image sensor,and the damage mechanism of performance degradation induced by total dose irradiation was revealed in 4T-PPD CMOS image sensor.The main contents of this paper are as follows:(1)Based on the real technology structure and parameters of pixel unit of the4T-PPD CMOS image sensor,the pixel unit model of 4T-PPD CMOS image sensor is constructed by TCAD.In this TCAD simulation model,we consider the following model: optical generation model,carrier mobility,SRH recombination,the defect model about trapped positive charge and the radiation mode.We have achieved some physical processes,including the dynamic transition process of the pixel unit,the photoelectric effect of the photodiode and the simulation of the total dose effect based on the positive charge trapped.(2)Based on the total ionizing dose effect model of the positive charge trapped,the distribution and change of the positive charge trapped in the pixel unit were observed,and the sensitive region of the degradation of the pixel unit was detected bythe total ionizing dose irradiation by TCAD simulation.Based on the relationship between the output voltage of the pixel unit and the dark current in the dark environment,we simulated the degradation rule of the output voltage of the pixel unit with the total ionizing dose under the dark environment,and qualitatively analyzed the degradation rule of the dark current.The experiment result by the60 Co ?-rays source was used to verify the degradation of the dark current with the total ionizing dose in the TCAD model.(3)Based on charge transfer path,the potential pocket model,potential barrier model and the hybrid model of the potential pocket and potential barrier are constructed.The degradation rule of charge transfer path of total ionizing dose effect is analyzed,and the electric field intensity distribution and potential distribution of oxide layer are studied.And the degradation mechanism of image lag induced by total ionizing dose effect was explored by analyzing the degradation of 4T-PPD CMOS image sensor.