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

Abstract

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 (VT) degradation mechanism and found that the VT shifts of SONOS cells depend on the charge state; simply programming the cell to a higher VT cannot compensate for the radiation induced VT loss. The off-state current (Ioff) increase in the SONOS cell is also studied in this paper. Both VT and Ioff degradation would affect the memory system. Read data failures are mainly caused by VT shifts under irradiation, and program and erase failures are mainly caused by increased Ioff, 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.