Comparison of Analytical Models and Experimental Results for Single Event Upset in CMOS SRAMs

In an effort to design fully radiation-hardened memories for satellite and deep space applications, a 16K and a 2K CMOS static RAM were modeled for single-particle upset during the design stage. The modeling resulted in the addition of feedback resistors in the 16K, while the 2K remained tentatively unaltered. Subsequent experiments, using the Lawrence Berkeley Laboratories´ 88-inch cyclotron to accelerate krypton and oxygen ions, established an upset threshold for the 2K and the 16K without resistance added, as well as a hardening threshold for the 16K with feedback resistance added. Results for the 16K showed it to be hardenable to a higher level than previously published data for other unhardened 16K RAMs. The data agreed fairly well with the modeling results; however, a close look suggests that modification of the simulation methodology is required to accurately predict the resistance necessary to harden the RAM cell.