A Low-Complexity Retention Noise Parameter Estimation For MLC NAND Flash Memory

Retention noise is one of key components which impact negatively the reliability of NAND flash memory. It's essential to apply a mechanism which can recover data from long-time retention noised devices. The challenge is that the parameters, mean and variance, of retention noise vary with retention time. In this paper, a low-complexity two-stage method is proposed to estimate the parameters of retention noise. The first stage is to give an initial choice of the test state and two corresponding read sensing reference voltages by which a three-region voltage partition of this state is determined. Utilizing the relation between noise parameters and ratios of samples located in these properly selected voltage regions, initial estimates of mean and variance are acquired. The second stage is to find out new read sensing reference voltages of another state by employing these initial estimates. Then. refined estimates of mean and variance can be acquired by similar processing performed in the first stage. Numerical results show that the proposed method can estimate channel parameters accurately and extend retention time effectively.