Comprehensive analysis of retention characteristics in 3-D NAND flash memory cells with tube-type poly-Si channel structure

Retention characteristics of a 3-D NAND flash cell with tube-type poly-Si body are investigated at a high temperature (T) depending on program (P), neutral (N), and erase (E) states of adjacent cells. The trap density (N_t) in the nitride storage layer of the cell is extracted by utilizing retention model and deriving related equations in cylindrical coordinate. By programming or erasing adjacent cells, we can separate laterally distributed charge component from the retention characteristics. The adjacent cells which are programmed suppress significantly the lateral diffusion at a high T so that we can extract accurate N_t profile. Extracted peak of N_t at P-P-P mode is ~1.2×10¹⁹ cm^-3eV^-1 at an E_C-E_T of 1.0 eV. Retention characteristics with effective gate length and word-line biasing are also investigated.