Random Telegraph Noise Intensification After High-Temperature Phases in 3-D NAND Flash Arrays

In this letter, we present clear experimental evidence proving that a high-temperature idle/data-retention phase gives rise to a permanent intensification of random telegraph noise (RTN) in 3-D NAND Flash arrays. The magnitude of RTN intensification is shown to be strongly dependent on the threshold-voltage level on which cells spent the high-temperature phase and to be independent of the backpattern of the NAND string. The effect is explained in terms of depassivation of some traps at the grain boundaries of the polysilicon channel of the memory cells during the high-temperature phase, leading to stronger nonuniformities in channel inversion and to a higher number of defects active in the RTN process. The reported phenomenology represents an addition idle/data-retention issue and another constraint to the noise margins of 3-D NAND Flash arrays.