Effect of Lateral Charge Diffusion on Retention Characteristics of 3D NAND Flash Cells

Abstract

Retention characteristics of 3D NAND Flash cells are investigated at various temperatures ( {T} ) depending on the degree of program and erase. The \Delta {V} {\text {th}} for each condition is compared to understand the degradation of the retention characteristics attributable to vertical loss and/or lateral diffusion. In addition, the relationship between Program/Erase (PE) window (PGM {V} {\text {th}} - Erase {V} {\text {th}} ) and \Delta {V} {\text {th}} are analyzed. In the case when PGM {V} {\text {th}} is the same, the \Delta {V} {\text {th}} decreases as the PE window decreases. At temperatures below 150 °C, \Delta {V} {\text {th}} and PE window show linear relationship, and as PE window decreases, \Delta {V} {\text {th}} also decreases to 0. On the other hand, at 250 °C, \Delta {V} {\text {th}} has a non-zero value even if PE window decreases to 0, thus has a non-linear relationship. The measurement results show that the lateral diffusion has a great influence on the short-term retention of 3D NAND flash cells.