Optimal dummy word line condition to suppress hot carrier injection phenomenon due to the natural local self-boosting effect in 3D NAND flash memory

Abstract

The main cell channel in 3D NAND flash structures easily goes into the floating state, because it is not directly connected to the substrate, resulting in the down-coupling phenomenon (DCP). As DCP reduces the boosting potential of the inhibit string during the program and verify operations, the natural local self-boosting (NLSB) effect is reduced, which in turn reduces the channel potential and causes a program disturb. However, if the channel potential of the selected word line (WL) is significantly increased by excessive NLSB, a hot carrier injection (HCI) occurs due to the potential difference between the adjacent WLs, even at a low channel potential. Therefore, we introduced a dummy WL to reduce HCI.