Least Squares Based Coupling Cancelation for MLC NAND Flash Memory with a Small Number of Voltage Sensing Operations

The cell-to-cell interference (CCI) becomes the major source of distortion in NAND Flash memory as the feature size continuously decreases. As a result, removing the interference is crucial to ensure storage reliability while increasing the memory density. Along with the CCI, data retention also becomes a problem because only a small number of charges are stored at each cell. In this research, we propose a CCI cancelation algorithm that can remove or mitigate the CCI even when the data retention noise is fairly large. The coefficients for the proposed CCI canceler are adaptively found by minimizing the estimation error of the CCI, and the least squares method is used for the optimization. To reduce the number of voltage sensing operations, optimal multi-level memory sensing schemes for the proposed CCI canceler are studied. The developed algorithm is applied to both simulated and real NAND Flash memory, and it is demonstrated that the CCI canceler significantly lowers the bit error rate (BER) of multi-level cell (MLC) NAND Flash memory.