Proton-Induced Single Event Upsets in NMOS Microprocessors

This paper reports an investigation of single event upsets induced in 16-bit NMOS microprocessors by 40-MeV protons. The results obtained in this study are compared with previous reported studies of upset rates in a neutron beam of average energy 14 MeV. The microprocessors investigated were the MC68000 and various versions of the Z8002 and the AMZ8002. Proton fluence per upset was in the range of 2 × 109 to 4 × 1010 protons/cm2, depending on the device type. Device failure ocurred after total fluence of 3.2 × 1010 to 1.7 × 1011 protons/cm2, corresponding to a total dose of 6.0 to 32.2 kRad(Si), again depending on the device type. The typical proton fluence per upset was approximately an order of magnitude less than the previously-measured neutron fluence for upset, meaning the devices are more sensitive to 40-MeV proton upset than to 14-MeV neutron upset. In addition, the sensitivity to upset for some of the microprocessors was dependent on the previous radiation exposure of the device. Large variations in fluence per upset and dose to failure were found between different versions of the same microprocessor type. A limited investigation showed no marked dependence of the upset rate on flux.