High-density 3D-NAND flash with dual-string select line (D-SSL)

Abstract

In this study, high-density 3D-NAND flash memory is proposed. Using D-SSL, lateral shrink of cell area can be achieved by distinguishing two strings in a word-line (WL). We verify erase/program and read characteristics using technology computer-aided design (TCAD) simulations with rigorous calibrated condition. The proposed high density NAND flash has normally-on state SSLs through additional process and electrical treatment. In the conventional reference NAND flash, the cell string connected to the bit-line (BL) is distinguished by WL cut (WLC). On the other hand, in the proposed high density NAND flash, the cell string is selected by utilizing the normally-on state SSLs using trapped hole and doped arsenic at the intersection of SSL1 and SSL2. Compared with the conventional scheme, the proposed D-SSL exhibits almost same erase/program and read characteristics. Consequently, the proposed D-SSL scheme can increase memory density with reduced number of WLCs by distinguishing strings using D-SSL.