Threshold-Voltage Instability Due to Damage Recovery in Nanoscale NAND Flash Memories

Impact of the array background pattern on cycling-induced threshold-voltage instabilities in nanoscale NAND Flash memories

“…3. Results reveal, first of all, the typical increase of a with the initial V T level of the victim cells [5], coming from a dependence of the detrapping rate on the electric field in the cell tunnel-oxide during bake. Besides, results clearly highlight that the value of a of the victim cells on level L1 increases by about a factor of 2:5 when moving from the E; E; E; E to the L3; L3; L3; L3 BP of the aggressor cells.…”

“…where t à B is the equivalent time elapsed between the end of cycling and the first read operation on the array [5]. From the fitting, the slope a of the logarithmic trend can be extracted as a function of the state of the victim and of the aggressor cells, as shown in Fig.…”

“…Instabilities are mainly the result of charge detrapping from the tunnel oxide of the memory cells, giving rise to unwanted displacements of their V T during idle/bake periods [1][2][3][4][5][6][7][8]. Although the statistical nature of the detrapping process and, in turn, of the resulting V T shift (DV T ) has been clearly recognized [3,6,9,10], an average reduction of V T as time elapses is the typical feature of detrapping in Flash arrays, owing to a dominant neutralization of negative charge in the cell tunnel-oxide [3][4][5]7]. This negative DV T is particularly detrimental for multi-level devices where the increase of storage density is traded off with the reduction of noise margins [11].…”

Reliability of NAND Flash Memories: Planar Cells and Emerging Issues in 3D Devices

“…Such task began in [221,222] and developed into a full model accounting for the major experimental evidence in [223][224][225]. Figure 19 shows experimental data from a retention experiment at room temperature on a 16 nm NAND vehicle after 10 4 P/E cycles [226]. Note the difference with respect to Figure 16 (right): no specific tail is detected here, but rather the entire distribution is affected, although different charge loss rates can be detected between the main part and the lower extreme of the distribution (see right-hand side of Figure 19).…”

“…We start this Section with the description of a compact model [221,222,226] that captures the main features of the data and can be used for some first-order extrapolations, while moving to more refined descriptions of the underlying physics later on. To this aim, we assume a log-time dependence of the V T shift that, considering that the first read operation is performed at time t 0 after the end of the cycling phase, leads to…”