Non-volatile memory and methods with soft-bit reads while reading hard bits with compensation for coupling

摘要

A non-volatile memory has its cells' thresholds programmed within any one of a first set of voltage bands partitioned by a first set of reference thresholds across a threshold window. Hard bits are obtained when read relative to the first set of reference thresholds. The cells are read at a higher resolution relative to a second set of reference thresholds so as to provide additional soft bits for error correction. The soft bits are generated by a combination of a first modulation of voltage on a current word line WLn and a second modulation of voltage on an adjacent word line WLn+1, as in a reading scheme known as “Direct-Lookahead (DLA)”.

主权项

1. A method of reading a group on memory cells on a word line, comprising:
partitioning a threshold window of the memory cells using a first set of reference thresholds into a first set of threshold voltage bands; coding the first set threshold voltage bands with a first set of bits; sensing an adjacent group of memory cells on an adjacent word line to determine respective programmed states and associated coupling levels due to charges stored in neighboring memory cells on individual memory cells in the current group on the current word line, the coupling levels including a nominal coupling level corresponding to a substantially unprogrammed state in neighboring memory cells; sensing the current group of memory cells by permuting a current word line voltage selected from the first set of reference thresholds and an adjacent word line voltage selected from a set of bias voltages obtained as a function of different associated coupling levels; obtaining the first set of bits when the bias voltage during the permutation corresponds to the nominal coupling level; and obtaining a second set of bits when the bias voltage during the permutation corresponds to other than the nominal coupling level.