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Novel WOM codes that have the potential to achieve over 90% of the Sum-Rate limit and increase the lifetime capacity of NAND flash memory.

Background

NAND flash memory has become an indispensable part of today’s digital life. The NAND flash memory market was valued at USD 66.52 billion in 2021, and is expected to reach a value of USD 94.24 billion by 2027. This growth is being driven by the demand for consumer devices as well as fast and reliable enterprise data storage solutions. This technology has the potential to increase the lifetime capacity of NAND flash memory to over 90% of the theoretical Sum‑Rate limit.

Technology Overview

NAND flash memory relies on the use of semiconductor single floating gate transistors that have fixed lifetime maximum limits for the number of on-off switch cycles. Solid State Drives (SSDs) use NAND flash memory assemblies in a form where the transistors are grouped in pages and blocks. An entire block needs to be erased in order to write new data. Due to the physical limits of the transistors, flash memory can only endure a finite number of program and erase cycles. This limit is often described as the theoretical Upper Bound (C). 

Write Once Memory (WOM) codes control how information is encoded in the transistors of a SSD to optimize the use of flash memory cells for speed and lifetime capacity. The Sum-Rate (R_sum) of WOM codes is the ratio between the number of writes and the number of memory cells used for encoded storage. At high Sum-Rates, current WOM codes and SSD controllers are able to achieve only about 50% of the theoretical limit. This technology has the potential to achieve over 90% of the theoretical limit, as shown in figure 1 below.