Threshold Voltage Fluctuation by Random Telegraph Noise in Floating Gate nand Flash Memory String

Read current fluctuation (ΔI_read) due to random telegraph noise was measured from a cell in a NAND flash memory cell string, and its effect on threshold voltage fluctuation (ΔV_th) was analyzed. Sixteen-level fluctuation (four traps) was observed in a 60-nm cell of a cell string (ΔI_read/I_read of ~0.4). ΔI_read increased with decreasing L_g, and ΔI_read/I_read up to 0.75 was observed at 48 nm. ΔI_read, ΔV_th, and their relation were clearly analyzed with program/erase mode of a cell and pass cells in a string. Although ΔI_read is largest when a read cell and pass cells are erased, ΔV_th is largest when a read cell is erased and pass cells are programmed in a cell string. We also observed the specific noise amplitude under various conditions, such as the bit-line bias, the pass bias of unselected cells in the NAND strings, and the temperature.