Observation of Alpha Particle Effects in the Charge-Coupled Image Sensor

Alpha particle effects in the charge-coupled (CCD) image sensor were evaluated by using Am-241, Th, and Po-210 radiation sources. Soft error rate due to alpha particle hit was dependent upon alpha energy spectrum and on integration time and photogate bias of the device. The device was operated at frequencies between 200 kHz and 1 MHz during the irradiation and was found to have no effect on the soft error rate. A charge collection efficiency of 64% was observed as the device was exposed to a 4.2-MeV alpha. Material-asssociated characteristics such as diffusion length and lifetime of the minority carrier were calculated from the outcome of the charge collection efficiency. More than two orders of magnitude in increase of dark signal and charge transfer loss were observed as the device was subjected to a total radiation exposure of 105 rads (Si). The device degradation is due mainly to the threshold voltage shift and lattice defects.