Investigation of the random telegraph noise instability in scaled Flash memory arrays

This paper investigates the main features of the random telegraph noise statistical instability in Flash memory arrays. The exponential tails introduced in the cumulative distribution of the threshold voltage variation between two subsequent read operations on the cells are shown to be preserved when the available statistics is increased. Large threshold voltage instabilities are therefore to be admitted, requiring the possibility for large random telegraph noise fluctuation amplitudes and the superposition of multi-trap random telegraph noise effects. Moreover, tails drift for increasing elapsed time between the compared read operations due to the activation of slower and slower traps in the random telegraph noise process, whose effect should be carefully considered in drawing reliability projections. Finally, the results for an early and an optimized NOR process are presented, showing non-negligible differences in their exponential tails behavior and revealing the existence of important parameters other than the technology node feature size having a significant impact on the random telegraph noise instability.