Detector for MLC NAND Flash Memory Using Neighbor-A-Priori Information

Cell-to-cell interference (CCI), arising from parasitic coupling-capacitance between adjacent cells, is a major factor for the degradation of cell threshold voltage in today's flash memory chips. In this paper, three novel postprocessing detection schemes that exploit the a priori information of neighboring/interfering cells for mitigating the CCI effect in multilevel cell NAND flash memory are presented. The proposed schemes are referred to as the Even-A-Priori (Even-AP), the All-A-Priori (All-AP), and the All-AP-coupling-capacitance ratio (CCR) detectors. The main idea is to remove the CCI component from the interfering cells before CCI cancellation from the victim cell. Specifically, the mean CCRs along the victim cell's vertical and diagonal directions are estimated to enable more accurate CCI cancellation. Performance analysis and simulation results show that the channel signal-to-noise ratio performance can be improved by up to 2 dB at a cell storage capacity of 1.8 bits/cell, which is significantly improved compared with some prior-art detection schemes.