Channel Potential of Bandgap-Engineered Tunneling Oxide (BE-TOX) in Inhibited 3D NAND Flash Memory Strings

In this study, the channel potential of inhibited strings in 3D NAND flash memory using a bandgap-engineered tunneling oxide (BE-TOX) structure is analyzed. The equivalent oxide thickness (EOT) of the structure using BE-TOX was designed to be the same as the conventional 3D NAND flash memory, and the channel potentials of the down coupling phenomenon (DCP) and natural local self-boosting (NLSB) effect were analyzed. As a result, the BE-TOX structure was confirmed to have a higher channel potential in the DCP and NLSB than the conventional structure, making it relatively effective for program disturbance. The main reason for the difference in the channel potential between the BE-TOX and conventional structures is that adjacent cells have different threshold voltages (V_th). When the same program voltage (V_PGM) and program time (T_PGM) were applied during the program operation, V_th decreased in the BE-TOX structure, which increased the channel potential when DCP and NLSB occurred. Finally, a simulation was conducted by varying the thicknesses of the oxide and nitride in the BE-TOX structure. Despite the EOT being fixed and the thicknesses of both nitride and oxide being varied, the channel potential was affected.