Electrostatic effect of localised charge in dual bit memory cells with discrete traps

In this paper, the electrostatic impact of channel hot electron (CHE) injection in discrete-trap memories is quantitatively addressed. The dual bit behavior of the transfer characteristics during forward and reverse read of a written cell is thoroughly analysed with the help of an analytical model. Such a model allows, for the first time, to estimate the effective charged portion of the discrete storage layer, L₂, and the quantity of electrons, Q, injected in the trapping sites from the experimental parameters of the I_d-V_g characteristics, the reverse-forward threshold voltage shift ΔV_RF, and the total threshold voltage shift ΔV_tot. The viability of this model is confirmed with tests performed on nanocrystal memories, under different bias conditions. These results are confirmed with the help of a 2D drift-diffusion commercial code (ATLAS-SILVACO).