Memory system that determines a type of stress of a memory device
According to some embodiments, a memory system includes a memory device including a plurality of memory cells capable of storing a plurality of bit data corresponding to a plurality of levels, respectively, and a controller configured to read data from the memory device, perform an error correction when there is an error in the read data, and determine a variation in a level before and after error correction of the read data.
1. A memory system comprising:
a memory device including a plurality of memory cells capable of storing m bits data corresponding to threshold voltages of an m-th power of two, m being a natural number of two or more;
a controller configured to
read data from the memory cells,
perform an error correction when there is an error in the read data,
determine a variation between the threshold voltage of the read data before the error correction is performed and the threshold voltage of the read data after the error correction is performed, and
determine a type of stress of the memory device based on the number of memory cells having variation of the threshold voltage and a direction of the variation of threshold voltage, the direction of the variation including information as to whether the threshold voltage of the read data before the error correction is performed is lower or higher than the threshold voltage of the read data after the error correction is performed.
2. The memory system according to claim 1 ,
wherein the controller is further configured to determine a strength of a stress of the memory device based on the number of memory cells having variation of the threshold voltage and the direction of the variation of threshold voltage.
3. The memory system according to claim 2 , wherein the controller is configured to adjust a read voltage based on the determined type of stress of the memory device and the determined strength of stress of the memory device.
4. The memory system according to claim 1 , wherein the controller is further configured to store the number of memory cells having variation of the threshold voltage and a direction of the variation of threshold voltage.
5. The memory system according to claim 1 , wherein the controller is configured to determine the variation between the threshold voltage of the read data before the error correction is performed and the threshold voltage of the read data after the error correction is performed, while there is no access from an external device.
6. The memory system according to claim 1 , wherein
the memory device is configured to read data in a unit of a page from the memory cells,
the plurality of memory cells corresponds to m pages, and
the controller is configured to perform the error correction on the one page of the m pages when there is an error in the one page and determine the variation between the threshold voltage of the read data before the error correction is performed and the threshold voltage of the read data after the error correction is performed by using data of the one page where the error correction is performed and data of the (m−1) pages.
7. A method of determining level variations in a memory device that includes a plurality of memory cells, the method comprising:
storing m bits data corresponding to threshold voltages of an m-th power of two, m being a natural number of two or more;
reading data from the memory cells;
performing an error correction when there is an error in the read data;
determining the variation between the threshold voltage of the read data before performing the error correction and the threshold voltage of the read data after performing the error correction;
determining a type of stress of the memory device based on the number of memory cells having variation of the threshold voltage and a direction of the variation of threshold voltage, the direction of the variation including information as to whether the threshold voltage of the read data before performing the error correction is lower or higher than the threshold voltage of the read data after performing the error correction; and
determining the variation between the threshold voltage of the read data before performing the error correction and the threshold voltage of the read data after performing the error correction to specify the number of memory cells having variation of the threshold voltage and a direction of the variation of threshold voltage.
8. The method according to claim 7 , further comprising:
storing the number of memory cells having variation of the threshold voltage and a direction of the variation of threshold voltage.
9. The method according to claim 7 , further comprising:
determining a strength of a stress of the memory device based on the number of memory cells having variation of the threshold voltage and the direction of the variation of threshold voltage.
10. The method according to claim 9 , further comprising adjusting a read voltage based on the determined type of stress of the memory device and the determined strength of stress of the memory device.
11. The method according to claim 7 , wherein the determining the variation between the threshold voltage of the read data before performing the error correction and the threshold voltage of the read data after performing the error correction occurs while there is no access from an external device.
12. The method according to claim 7 , wherein
the memory device is configured to read data in a unit of a page from the memory cells,
the plurality of memory cells corresponds to m pages, and
the performing an error correction includes performing the error correction on the one page of the m pages when there is an error in the one page, and
the determining the variation between the threshold voltage of the read data before performing the error correction and the threshold voltage of the read data after performing the error correction uses data of the one page where the error correction is performed and data of the (m−1) pages.