IMPLICATIONS OF THE SPATIAL DEPENDENCE OF THE SINGLE-EVENT-UPSET THRESHOLD IN SRAMS MEASURED WITH A PULSED-LASER

Pulsed laser light was used to measure single event upset (SEU) thresh olds for a large number of memory cells in both CMOS and bipolar SRAMs . Results showed that small variations in intercell upset threshold co uld not explain the gradual rise in the curve of cross section versus linear energy transfer (LET). The memory cells exhibited greater intra cell variations implying that the charge collection efficiency within a memory cell varies spatially and contributes substantially to the sh ape of the curve of cross section versus LET. The results also suggest that the pulsed laser can be used for hardness-assurance measurements on devices with sensitive areas larger than the diameter of the laser beam.