Nonvolatile semiconductor memory device
View Patent ↗A nonvolatile semiconductor memory device comprises a memory cell array including a plurality of memory cells, and a control circuit for the memory cell array. The control circuit is configured to perform a pre-read operation to read pre-selected memory cells before a read operation on target memory cells is performed and to change a read voltage to be applied to the target memory cells during the read operation based on a result of the pre-read operation.
1. A nonvolatile semiconductor memory device comprising:
a memory cell array including a plurality of memory cells; and
a control circuit for the memory cell array,
wherein the control circuit is configured to perform a pre-read operation to read pre-selected memory cells before a read operation on target memory cells is performed and to change a read voltage to be applied to the target memory cells during the read operation based on a result of the pre-read operation, and
wherein the pre-selected memory cells include none or less than all of the target memory cells.
2. The device according to claim 1 ,
wherein the pre-selected memory cells include some of the target memory cells.
3. The device according to claim 1 ,
wherein the memory cell array includes dummy memory cells that are different from the target memory cells, and
the dummy memory cells are set as the pre-selected memory cells to be read in the pre-read operation.
4. The device according to claim 1 ,
wherein the control circuit is configured to correct an amount of the read voltage changed during the read operation based on a total number of write or erase operations performed on the memory cell array.
5. The device according to claim 1 , further comprising:
word lines stacked on a substrate, each of the word lines connected to a different group of memory cells,
wherein the control circuit is configured to correct an amount of the read voltage changed during the read operation according to a distance from the substrate of the word line that is connected to the target memory cells.
6. The device according to claim 1 ,
wherein the memory cells each have a semiconductor layer, and
the control circuit is configured to correct the amount of the read voltage changed during the read operation according to diameters of the semiconductor layers of the target memory cells.
7. The device according to claim 1 ,
wherein the number of fail bits is counted during the pre-read operation, and
a read voltage to be applied to the memory cells during the read operation is changed according to the number of fail bits.
8. The device according to claim 1 ,
wherein during the pre-read operation, the read voltage is gradually changed, and
the read voltage to be applied to the memory cells during the read operation is changed according to a rate of increase in the number of memory cells having a threshold voltage lower than the read voltage, as the read voltage is gradually changed.
9. A nonvolatile semiconductor memory device comprising:
a memory cell array including a plurality of memory cells, each of the memory cells having a semiconductor layer; and
a control circuit for the memory cell array,
wherein the control circuit is configured to perform a pre-read operation to read pre-selected memory cells before a first read operation on a first group of target memory cells is performed and a second read operation on a second group of target memory cells is performed, and to change a read voltage to be applied to the first group of memory cells during the first read operation and the second group of memory cells during the second read operation, based on a result of the pre-read operation and diameters of the semiconductor layers of the first and second groups of memory cells.
10. The device according to claim 9 , wherein the diameters of the semiconductor layers of the first group of memory cells are each equal to a first diameter and the diameters of the semiconductor layers of the second group of memory cells are each equal to a second diameter that is different from the first diameter.
11. The device according to claim 10 , wherein the control circuit is configured to change a read voltage to be applied to the first group of memory cells during the first read operation by a first amount and change a read voltage to be applied to the second group of memory cells during the second read operation by a second amount that is different from the first amount.
12. The device according to claim 11 , wherein the first diameter is larger than the second diameter and the first amount is smaller than the second amount.
13. A method of controlling a nonvolatile semiconductor memory device having a memory cell array that includes a plurality of memory cells, the method comprising:
performing a pre-read operation to read pre-selected memory cells before a read operation on target memory cells;
changing a read voltage that is to be applied to the target memory cells during the read operation based on a result of the pre-read operation; and
performing the read operation on the target memory cells;
wherein the pre-selected memory cells include none or less than all of the target memory cells.
14. The method according to claim 13 ,
wherein the pre-selected memory cells include some of the target memory cells.
15. The method according to claim 13 ,
wherein the memory cell array includes dummy memory cells that are different from the target memory cells, and
the dummy memory cells are set as the pre-selected memory cells to be read in the pre-read operation.
16. The method according to claim 13 , further comprising:
correcting the read voltage that is to be applied to the target memory cells during the read operation based on a total number of write or erase operations performed on the memory cell array.
17. The method according to claim 13 , wherein the nonvolatile semiconductor memory device has word lines stacked on a substrate, each of the word lines connected to a different group of memory cells, the method further comprising:
correcting the read voltage that is to be applied to the target memory cells during the read operation according to a distance from the substrate of the word line that is connected to the target memory cells.
18. The method according to claim 13 , wherein the memory cells each have a semiconductor layer, the method further comprising:
correcting the read voltage that is to be applied to the target memory cells during the read operation according to diameters of the semiconductor layers of the target memory cells.
19. The method according to claim 13 ,
wherein the number of fail bits is counted during the pre-read operation, and
a read voltage to be applied to the memory cells during the read operation is changed according to the number of fail bits.
20. The method according to claim 13 ,
wherein during the pre-read operation, the read voltage is gradually changed, and
the read voltage to be applied to the memory cells during the read operation is changed according to a rate of increase in the number of memory cells having a threshold voltage lower than the read voltage, as the read voltage is gradually changed.