Cell Pattern Dependency of Charge Failure Mechanisms During Short-Term Retention in 3-D NAND Flash Memories

Abstract

In this letter, we analyzed charge failure mechanisms depending on cell patterns during short-term retention in 3-D NAND flash memories. In the previous study, we have separated complex retention characteristics into three charge failure components using a stretched exponential function. Vertical charge failure components with very small time-constants have almost no dependency between the solid pattern (S/P) and checker-board pattern (C/P). However, the lateral migration (LM) component affected by the lateral electric field (E-field) shows strong dependency on the cell patterns. When Program verify (PV) level decreases, the lateral E-field decreases and the pattern dependency disappears. Finally, we revealed that the difference in the short-term retention characteristics according to the cell patterns is due to LM component, and demonstrated that almost the same retention characteristics would be obtained at low PV levels regardless of the cell patterns.