TOTAL-DOSE DEPENDENCE OF SOFT-ERROR HARDNESS IN 64KBIT SRAMS EVALUATED BY SINGLE-ION MICROPROBE TECHNIQUE

Total dose effect on the soft-error susceptibility of 64kbit CMOS SRAM has been investigated by using the single ion microprobe technique wh ich enables us to get a map of soft-error sensitivity in a memory cell by hitting a micron-size area with single ions. The effects of the io n dose on the susceptibility of each error-sensitive site have been ev aluated. The errors due to the upset of p-MOSFETs have become more sus ceptible at higher dose while that of the n-MOSFETs less susceptible. One of the origins of the errors are the negative threshold voltage(V- th) shifts of the MOSFETs which are caused by oxide trapped charges. D isplacement damage induced by ion irradiation also affects the suscept ibility to the soft-error.