Comparison of the total-dose and 60 MeV proton-irradiation response of CMOS transistors operated at 4.2 K

When developing cryogenics read-out electronics for focal-plane arrays, one has to consider the space radiation environment. The behaviour of CMOS transistor at 4,2 K before and after gamma and 60 MeV proton irradiation is investigated. Different split batches have been tested and particular interest points were the presence of a lowly doped drain (LDD), of a p-well or of a threshold voltage adjust implantation. Transistors with different lay-out, i.e regular and closed geometry devices have been compared. It appears that the total-dose response depends significantly on the processing split and on the device geometry. Non-LDD devices show better post-irradiation performance and are therefore recommended as radiation harder. The same applies, as expected, for closed geometry structures. The occurrence of some low temperature specific phenomena indicates that additional fundamental radiation mechanisms are operational at cryogenic temperatures, which requires further in-depth studies. (A.C.)