A 1-Tb, 4b/Cell, 176-Stacked-WL 3D-NAND Flash Memory with Improved Read Latency and a 14.8Gb/mm2 Density

Triple-level-cell (TLC) NAND has prevailed the non-volatile memory market, yet the quad-level-cell (QLC) NAND is emerging as a suitable replacement for low-cost and high-density storage. However, despite its cost effectiveness QLC's market share is not increasing quickly, not only due to its worse reliability but also its slow sequential and random read performance. To increase random read performance an independent plane read operation has been introduced [1], [2], but the read and pass voltage noise, caused by high I/O and data-path current consumption, causes a shift in the threshold voltage
$(\mathrm{V}_{\text{th}})$
distribution during plane-interleaved and cache read operations. Furthermore, for QLC with reduced program and erase (P/E) cycles the number raw bit errors exceeds the amount correctable by ECC. More read-retry steps need to be added to compensate, but the read latency increases.