Factors Contributing to Cmos Static Ram Upset

Phenomena contributing to transient radiation induced static RAM (SRAM) cell upset in CMOS integrated circuits (ICs) include rail span collapse, dynamic FET threshold voltage shifts, photocurrents internal to the RAM cell, secondary photocurrents, and lateral variations in silicon surface potential. Of these phenomena, it is found that the major contributors are rail span collapse and internal cell photocurrents. A model is presented which combines global rail span collapse calculations with detailed analyses of local effects in the ram cell.