Total Dose Response of the Z80A and Z8002 Microprocessors

Total dose effects are reported for two NMOS-technology microprocessors, the 8-bit Z80A and 16-bit Z8002. Specific failure modes and radiation-sensitive instructions are discussed, including the effect of clock frequency on the radiation failure level. Three different functional test methods are compared that differ in hardware complexity and diagnostic level. Significant variations were observed in the hardness of different date codes as well as between different manufacturers. The hardest devices failed at levels above 104 rad(Si). The use of terminal measurements to determine changes in the threshold voltage of internal MOS transistors is also discussed.