Assessment of Proton Direct Ionization for the Radiation Hardness Assurance of Deep Submicron SRAMs Used in Space Applications

Proton direct ionization (PDI) from low-energy protons has been shown to have a potentially significant impact on the accuracy of prediction methods used to calculate the upset rates (URs) of memory devices in space applications for state-of-the-art deep submicron technologies. The general approach nowadays is to consider a safety margin to apply over the UR computed from high-energy proton and heavy-ion experimental data. The data reported here present a challenge to this approach. Different UR prediction methods are used and compared in order to establish the impact of PDI on the total UR. Regardless of the method employed, the findings suggest that PDI can contribute to up to 90% of the total UR, on average, for a general selection of space orbits, with peaks of up to 99%. Such results suggest that an approach based on the characterization of the low-energy portion of the proton spectrum would be more convenient for similar technologies than the application of a general safety margin. Based on data presented here, the previously proposed margin of 5 is exceeded, by large amounts in some cases.