Get High Reliability from Your High-Density Flash

October 16, 2018 Gibson Ming-Dar Chen, UDinfo

NAND flash memory is the most popular non-volatile storage element that can be electrically programmed/re-programmed and erased. As technology continuously advances, the demands of greater density and better performance with flash memory grow as well.

Generally, there are three types of NAND flash: SLC (Single-Level Cell), MLC (Multi-Level Cell), and TLC (Tri-Level Cell). NAND makers recently announced a next generation, 3D TLC NAND, also known as three-bit per cell.

As the demand grows for solid-state drives (SSDs) in industrial/embedded, military, and medical applications, 3D TLC might not offer enough reliability. One way around that issue is to employ the memory’s SLC mode, a technique called Pseudo SLC (pSLC). Hence, 3D TLC can be a viable option for high program/erase (P/E) cycles and high performance.

The 3D TLC pSLC mode separates the threshold voltage into two parts and operates as a 1-bit cell as shown in the figure. Such operation can speed up the programming time and extend the endurance for single-cell memory. To implement pSLC on 3D TLC, the developer need only modify the SSD controller firmware, which reduces the capacity by two-thirds but extends the number of P/E cycles by 10X. In conclusion, the pSLC mode can dramatically increase the reliability of an SSD that’s designed with 3D TLC, the most cost-effective NAND available.

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