Heavy ion microscopy of single event upsets in CMOS SRAMs

The single event upset (SEU) imaging has been applied at the GSI heavy ion microprobe to determine the sensitivity of integrated circuits (IC) to heavy ion irradiation. This method offers the possibilty to directly image those parts of an IC which are sensitive to ion-induced malfunctions. By a 3-dimensional simulation of charge collection across p-n-micro-junctions we can predict SEU cross-sections. For a MHS65 162 2k x 8bit CMOS SRAM we found two regions per bit with different sensitivity and measured a total cross-section of (71 +/- 18)µm² for a bitflip per cell and simulated 60µm² with an argon beam of 1.4 Mev/nucl. (LET of 19.7 MeV/mg/cm²).