Total ionizing radiation effects of 2-T SONOS for 130 nm/4 Mb NOR flash memory technology

In this paper, we have studied the total ionizing dose (TID) radiation response up to 2 Mrad(Si) of silicon-oxide-nitride-oxide-silicon (SONOS) memory cells and memory circuits, fabricated in a 130 nm complimentary metal-oxide-semiconductor (CMOS) SONOS technology. We explored the threshold voltage (V-T) degradation mechanism and found that the V-T shifts of SONOS cells depend on the charge state; simply programming the cell to a higher V-T cannot compensate for the radiation induced V-T loss. The off-state current (I-off) increase in the SONOS cell is also studied in this paper. Both V-T and I-off degradation would affect the memory system. Read data failures are mainly caused by V-T shifts under irradiation, and program and erase failures are mainly caused by increased I-off, which overloads the charge pumping circuit. By varying the reference current, our 4 Mb NOR flash chip has the potential to survive a radiation dose of 1 Mrad(Si) in read mode.