Analysis on New Read Disturbance Induced by Hot Carrier Injections in 3-D Channel-Stacked NAND Flash Memory

Abstract

Read disturbance is analyzed in vertically channel-stacked NAND flash memory, which has string select transistors (SSTs) to access each channel layer independently. Additional read disturbance is observed at the cells adjacent to the selected cell in the unselected channel layers as well as typical read disturbance caused by repetitive Fowler–Nordheim tunneling (F-N) stress. Technology computer-aided design simulations and measurements are performed to investigate the disturbance mechanisms. It is found that bitline-side [common-source line-side] adjacent cell is disturbed by the hot carrier injection (HCI), which results from positively [negatively] boosted channel potential by the rising [falling] of the voltage ( ${V}_{\text {unsel}}$ ) applied to unselected cells, respectively. A novel read operation, in which the selected cells are maintained in turned on state during the ${V}_{\text {unsel}}$ rising/falling and then are restored to their own states, is proposed to suppress the occurrence of the HCIs. As a result, it is revealed that the HCI-induced read disturbances are successfully suppressed by the proposed method.