Three-Dimensional Simulation of Charge-Trap Memory Programming—Part II: Variability

Abstract

This paper investigates the statistical variability sources affecting the program operation of nanoscale charge-trap memories. Using the 3-D TCAD model presented in Part I of this work, featuring a Monte Carlo simulation approach to deal with discrete traps in the storage layer, atomistic doping in the substrate, and granular electron injection from the substrate to the storage layer, we consider the effect of three main variability sources impacting charge-trap memory programming: 1) the statistical process ruling electron injection and trapping; 2) the fluctuation in the number and position of the trapping sites; and 3) the statistical distribution of the threshold-voltage shift induced by stored electrons in presence of percolative substrate conduction. We show that the first variability source plays the dominant role in determining the statistical dispersion of cell threshold voltage during the program operation.