Memory system having NAND-type flash memory and memory controller with shift read controller and threshold voltage comparison module

摘要

According to one embodiment, a memory system includes a NAND-type flash memory and a memory controller. A comparison module of the memory controller compares a first threshold voltage distribution of a first memory area with a second threshold voltage distribution of the first memory area acquired earlier than the first threshold voltage distribution, if an error is detected in data read from the first memory area. An error factor determination module of the memory controller determines a cause of the error based on the comparison result, and inhibits a data move operation of moving data of the first memory area to the second memory area based on the determination result.

主权项

1. A memory system comprising:
a NAND-type flash memory comprising a plurality of memory areas including a first memory area and a second memory area, each of the plurality of memory areas comprising a plurality of memory cells, and each of the plurality of memory cells storing one of a plurality of values; and a memory controller configured to control the NAND-type flash memory, wherein the memory controller comprises:
a shift read controller configured to execute shift read for reading data from at least part of the memory area of the NAND-type flash memory by changing a read level of each of the values, if an error is detected in data read from the memory area, wherein the error is detected based on an error correcting code added to the data;a threshold voltage distribution acquisition module configured to detect threshold voltages of at least part of the memory cells in the memory area based on a result of the shift read executed by the shift read controller, and to acquire threshold voltage distribution data representing a threshold voltage distribution of each of the values by acquiring the number of memory cells of each of the detected threshold voltages;a table in which the acquired threshold voltage distribution data is stored;a comparison module configured to compare first threshold voltage distribution data with second threshold voltage distribution data, if the first threshold voltage distribution data is acquired in accordance with detection of the error in read of first data from the first memory area, wherein the second threshold voltage distribution data is acquired in accordance with detection of the error in a read of second data from the first memory area and is stored in the table; andan error factor determination module configured to determine based on a result of the comparison whether a cause of the error is a first phenomenon in which a data write exerts influence on values of nearby memory cells as non-write targets, and to inhibit a data move operation of moving data of the first memory area to the second memory area in accordance with the error, if the cause of the error is the first phenomenon.