Memory system
According to one embodiment, a memory system includes a semiconductor memory and a controller. The memory system is capable of executing a first operation and a second operation. In the first operation, the controller issues a first command sequence, the semiconductor memory applies a first voltage to a first word line and applies a second voltage to a second word line to read data from the first memory, and the read data is transmitted to the controller from the semiconductor memory. In the second operation, the controller issues a second command sequence, the semiconductor memory applies a third voltage to the first word line and applies a fourth voltage to the second word line, and data held in the memory cell array is left untransmitted to the controller.
1. A memory system, wherein the memory system comprises:
a memory controller;
a plurality of memory cells; and
a plurality of word lines, wherein
a first word line of the plurality of word lines is coupled to a first memory cell of the plurality of memory cells;
a second word line of the plurality of word lines is coupled to a second memory cell of the plurality of memory cells;
a third word line of the plurality of word lines is coupled to a third memory cell of the plurality of memory cells;
the memory controller is configured to:
send a first command in response to receiving a read command from a host; and
send a second command in response to determining a shift voltage of the first command exceeds a first threshold and does not exceed a second threshold; and
the memory system is configured to:
apply a first set of voltages to the first word line, the second word line, and the third word line in response to the first command; and
apply a second set of voltages, different from the first set of voltages, to the first word line, the second word line, and the third word line in response to the second command.
2. The memory system of claim 1 , wherein
the first word line is adjacent to the second word line; and
the second word line is adjacent to the third word line.
3. The memory system of claim 1 , wherein no data is read from the plurality of memory cells in response to the second command.
4. The memory system of claim 1 , wherein data is read from a dummy word line of toe plurality of word lines in response to the second command.
5. The memory system of claim 1 , wherein the first set of voltages comprises:
a first voltage for the first word line and the third word line;
a second voltage for the second word line; and
a third voltage for a remaining set of word lines of the plurality of word lines, wherein the first voltage is higher than the third voltage.
6. The memory system of claim 1 , wherein the second set of voltages is a same voltage for each word line of the plurality of word lines.
7. The memory system of claim 1 , wherein the first threshold is a minimum acceptable index of a shift voltage table and the second threshold is a maximum acceptable index of the shift voltage table.
8. The memory system of claim 7 , wherein
the minimum acceptable index of the shift voltage table is associated with a first shift voltage;
the maximum acceptable index of the shift voltage table is associated with a second shift voltage; and
the second shift voltage is higher than the first shift voltage.
9. The memory system of claim 1 , wherein the memory controller is further configured to send a plurality of second commands until a number of second commands performed on a logical block associated with the plurality of word lines exceeds a predetermined threshold.
10. The memory system of claim 1 , the memory controller is further configured to reduce a shift voltage value associated with the shift voltage in response to sending the second command.
11. A method of managing a memory system, wherein the method comprises:
sending a first command in response to receiving a read command from a host;
sending a second command in response to determining a shift voltage of the first command exceeds a first threshold and does not exceed a second threshold;
applying a first set of voltages to a first word line, a second word line, and a third word line of a plurality of word lines in response to the first command; and
applying a second set of voltages, different from the first set of voltages, to the first word line, the second word line, and the third word line in response to the second command.
12. The method of claim 11 , wherein
the first word line is adjacent to the second word line; and
the second word line is adjacent to the third word line.
13. The method of claim 11 , wherein the method further comprises transmitting data to the host in response to the first command and not transmitting data to the host in response to the second command.
14. The method of claim 11 , wherein the method further comprises reading data from a dummy word line of the plurality of word lines in response to the second command.
15. The method of claim 11 , wherein applying the first set of voltages comprises:
applying a first voltage to the first word line and the third word line;
applying a second voltage to the second word line; and
applying a third voltage to a remaining set of word lines of the plurality of word lines, wherein the first voltage is higher than the third voltage.
16. The method of claim 11 , wherein applying the second set of voltages comprises applying a same voltage to each word line of the plurality of word lines.
17. The method of claim 11 , wherein the first threshold is a minimum acceptable index of a shift voltage table and the second threshold is a maximum acceptable index of the shift voltage table.
18. The method of claim 17 , wherein
the minimum acceptable index of the shift voltage table is associated with a first shift voltage;
the maximum acceptable index of the shift voltage table is associated with a second shift voltage; and
the second shift voltage is higher than the first shift voltage.
19. The method of claim 11 , wherein the method further comprises:
sending a plurality of second commands until a number of second commands performed on a logical block associated with the plurality of word lines exceeds a predetermined threshold.
20. The method of claim 11 , wherein the method further comprises:
reducing a shift voltage value associated with the shift voltage in response to sending the second command.