Total-Dose-Induced Threshold Voltage Shift Dependence on Tier Pitch in 3-D nand Flash Memories

The incessant scaling in the integration density of 3-D nand flash memories is mostly achieved through the combination of wordline (WL) stacking and reduction of the distance between WLs [tier pitch (TP)]. In this article, the impact of TP scaling on total ionizing dose (TID) sensitivity of 3-D nand flash cells is investigated in memories using charge-trap technology, in terms of threshold voltage shifts and raw bit errors. Experimental results show a mild dependence of TID effects on the TP. The physical mechanisms are discussed, and possible scaling trends are analyzed.