Electrons retention model for localized charge in oxide-nitride-oxide (ONO) dielectric

An electrons retention model for localized charge, trapped in ONO stacked dielectric, is introduced utilizing the nitride read-only memory (NROM) device. The observed reduction in threshold voltage (retention loss) of a programmed cell is explained in terms of lateral charge redistribution in the nitride layer. Assuming a thermal emission mechanism, the energy levels of the electrons traps were extracted and found to be distributed continuously in the nitride band gap, with a median value of /spl sim/2.12 eV below the conduction band. Utilizing these findings, the model allows a prediction of the retention loss over wide range of temperatures, between 140/spl deg/C-300/spl deg/C, long times, up to 10/sup 7/ s, large retention loss levels, /spl sim/90%, and programming windows, 1.9-3.3 V. Based on this work the ten-year relative retention loss at 140/spl deg/C of an NROM cell is expected to be 14% (V/sub DS/=0.1 V) and the equivalent uncycled product loss is expected to be 8%.