One-shot Read Processing to Enhance Cold Data Retention in Charge-trap TLC 3D NAND Flash

To address the retention concerns of cold data in 3D NAND flash memory, this work proposes a novel One-shot Read Processing (OSRP) scheme to improve data retention (DR) with lower error bits. In TLC 3D NAND with 96 storage layers, it is shown that the error bits from cells at high program states can be effectively lowered by OSRP and the dominant reason comes from minimized errors from cells at high program states. However, it is found that data retention with OSRP degrades at high-temperature (HT) on the contrary, and the dominant error bits come from charge loss in cells at low states. With in-depth analysis, the underlying mechanism could be OSRP-induced charge re-distributions (more effective to cells at lower states) to unstable shallow trap sites that can be easily activated at HT. Thereby, one-time OSRP can be adopted to strengthen cold data retention in 3D NAND applications like data centers, while it should be optimized to strengthen wide-temperature stabilities.