High-Precision Short-Term Lifetime Prediction in TLC 3-D NAND Flash Memory as Hot-Data Storage

Abstract

3D NAND flash memory is the ubiquitous non-volatile memory (NVM) on the market because of its large storage capacities, high reliability, and low bit-cost. The reliability characteristics of 3D NAND flash memory, however, are considerably different from those of 2D NAND flash memory due to the peculiar architectures. In this paper, read disturb (RD) at various program/erase (P/E) stages is thoroughly explored. To adjust the low-density parity check (LDPC) codes dynamically and extend the lifetime of 3D NAND flash memory, short-term lifetime prediction models of RD and endurance are proposed based on in-depth studies on the correlations of fail bit count (FBC) at various lifetime stages, and their accuracy is tested experimentally. A new short-term warning system (STWS) is proposed to extend the lifetime of 3D NAND-based storages. It consists of the error-bits’ prediction module (EBPM) and the self-adjustable low-density parity check codes module (SLDPC), where EBPM predicts FBC periodically and SLDPC pre-allocates LDPC codes for future use based on the result of EBPM. The experimental result shows that our prediction models have high reliability, and STWS can effectively prolong the lifetime of NAND flash. The findings of this study provide fundamental insights into FBC degradation in 3D NAND flash, as well as a simple and practical method for building 3D NAND-based storage with high reliability.