Radiation Response and Variability of Advanced Commercial Foundry Technologies

The radiation hardness of nominally identical SRAM test chips fabricated in five commercial foundries is examined. Large variations in single-event latchup and total dose response are observed. The softest SRAMs fail functionally at ~200 krad(SiO₂) and have a fairly large single-event latchup cross section. This is in contrast to the hardest foundry split which is nearly immune to single-event latchup at room temperature, and remains functional to a total dose of 400 krad(SiO ₂). Three of the splits show a similar increase in radiation induced leakage current, which is dependent on both the characterization bias as well as the pattern written to the memory array. The other two splits show neither a pattern nor a bias dependence on the leakage current. Heavy-ion microbeam experiments confirm that the most latchup sensitive area of these SRAMs is the peripheral circuitry, not the memory array itself. Qualification and hardened-by-design integrated circuit implications are discussed