Radiation effects in charge coupled devices

Radiation effects were investigated in experimental charge-coupled devices employing a 4-phase overlapping propagation structure with a 1700 A lower gate oxide and a 3700 A total upper gate oxide. Two surface channel devices and a peristaltic device were studied. The permanent ionizing radiation effects on the transfer efficiency, maximum output signal, and input transfer gate operating bias were measured, and the memory loss due to the effects of transient ionizing radiation was studied. The tolerance of charge-coupled devices to transient radiation is very low. The peristaltic device is saturated at about 0.3 rads (Si), while the surface channel device is filled with radiation-induced charge at a level of 2 rads. Results of neutron damage experiments show a relatively small effect on charge-up time, indicating that in the absence of ionizing radiation the 226-cell surface channel device could be operated at a delay time in excess of 0.1 sec after 50 trilion n/sq cm (1 MeV equivalent).