Azimuthal Charge Redistribution of Hemi-Cylindrical Vertical NAND Flash Memory

The reliability issues of the hemi-cylindrical (HC) vertical NAND (VNAND) flash memory are investigated with various channel hole remaining ratios (CHRRs). Unlike conventional VNAND cells, carriers are nonuniformly injected to the charge-trapping layer in the case of HC VNAND during program/erase operations. Hence, in addition to conventional lateral migration, a novel charge redistribution mechanism—-azimuthal redistribution (AR)—-is proposed. The simulation and experimental results indicate that AR is a major component of the data retention as a function of the CHRR of HC VNAND cells.