Investigation of Threshold Ion Range for Accurate Single Event Upset Measurements in Both SOI and Bulk Technologies

Experimental evidences are presented showing obvious differences in threshold ion range for silicon-on-insulator (SOI) and bulk static random access memories (SRAMs). Single event upset (SEU) cross sections of SOI SRAMs start to decline off the Weibull curve at ion ranges of 20.7 μm to 40.6 μm, depending on the ion species and also the thickness of metallization layers. Whereas for the bulk SRAMs, threshold range of Bismuth beam is unexpectedly larger than 60.4 μm. Underlying mechanisms are further revealed by Monte Carlo simulations and in-depth analysis. The relative location of ion´s Bragg peak to the sensitive region and also the position of ion LET in the σ-LET curve of test device turn out to be two key parameters in determining the threshold ion range which can explain the experimental results. Significant discrepancies are observed in the deposited energy spectrums in sensitive regions of bulk SRAM by ions at different sides of the Bragg peak, but with almost the same LET at die surface (all with ion range larger than 30 μm). Energy straggling of incident ions at the die surface is considered by Monte Carlo calculations. Implications for hardness assurance testing are also discussed. A formula is proposed for calculating the “worst case” threshold ion range.