Single-Event Upset in 3-D Charge-Trap NAND Flash Memories

Abstract

The effects of single-event upset (SEU) on the 2 threshold voltage (V-T) of a programmed cell in 3-D chargetrap (CT) NAND flash memory have been investigated using 3-D technology-computer-aideddesign (TCAD) simulations. After ion strikes, the surrounding electric field ( E- field) accelerates the generated holes into the CT layer (CTL), which lowers V-T of the programmed cell. The tunneling oxide (TOX) strike causes a more severe V-T shift than the blocking oxide (BOX) strike due to the higher E- field in the TOX layer. As the strike angle increases from 0 degrees(lateral) to 90 degrees (vertical), the effective irradiation volume is reduced, resulting in the mitigation of the SEU influence. Scaling of cell dimensions becomesmore vulnerable to SEU except for the thinner TOX.