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

This work describes the response of CMOS transistors fabricated in a 0.7 μm technology, which is adapted for cryogenic applications. The impact on the 4.2 K characteristics of total-dose γ-irradiation up to 100 krad is compared with exposure to 60 MeV protons in the fluence range 3×10¹⁰-10¹² cm^-2. Transistor arrays from different processing splits have been compared, in order to study the impact of Lightly Doped Drains (LDDs), a threshold voltage adjust implantation or a p-well on the cryogenic characteristics before and after the irradiation. Overall, it can be concluded that the technology shows sufficient hardness for the envisaged space mission. The observed radiation-induced changes in the main static device and circuit parameters are typically within a few per cent of the starting value, guaranteeing successful operation for the expected duration. Nevertheless, a few interesting observations have been made, concerning unusual radiation behaviour of the CMOS transistors, which are highlighted here. For the n-channel devices, a reduction of the 4.2 K drain current kink is reported, while the p-channel transistors show a rebound behaviour in the linear characteristics, after low to moderate proton fluences