Simulation of Proton Induced Single Event Upsets in Bulk Nano-CMOS SRAMs

Proton-induced single event upsets (SEUs) are a significant threat to reliability of integrated circuits (ICs) for working in harsh space environment. In this paper, a novel nested simulation model of static random access memory (SRAM) processed with 65nm bulk technology is built. The average charge collection coefficient of each sub-sensitive volume (SV) is calculated by point charge integration. The vulnerability of SRAM due to proton strike is evaluated using Monte Carlo simulation method based on the Geant4 simulation toolkit. The simulation results of protons with different energy show that the low energy protons can generate enough energy due to direct ionization and lead to high SEU cross-sections. For high-energy protons (>10MeV), SEU cross-sections increase with the increasing incident angle. For low-energy proton (<;10MeV), the cross sections of SRAMs reach the maximum at 63.4°. Moreover, multiple cell upsets (MCUs) can be caused by the recoil-ions generated from reactions of protons and tungsten layer. Finally, the SRAM cell spacing can evidently influence SEU cross-sections. Simulation results show that the mitigation effect of increasing cell spacing is weakened as the increase of incident proton energy. Thus, more attention must be paid when adopting the method that increasing cell spacing to mitigate the impact of proton radiation.