Semiconductor memory in which source line voltage is applied during a read operation

1. A semiconductor memory device comprising:

a memory cell;

a word line electrically connected to a gate of the memory cell; and

a source line electrically connected to a first end of the memory cell,

wherein in a read operation of the memory cell, a first voltage is applied to the source line in a first operation to determine whether or not a threshold voltage of the memory cell is above a first threshold value, a second voltage is applied to the source line in a second operation to determine whether or not the threshold voltage of the memory cell is above a second threshold value, and a third voltage is applied to the source line in a third operation to determine whether or not the threshold voltage of the memory cell is above a third threshold value.

2. The semiconductor memory device according to claim 1 ,

wherein a fourth voltage is applied to the word line during the first, second, and third operations.

3. The semiconductor memory device according to claim 2 , wherein a value of data stored in the memory cell is determined after the first, second, and third operations.

4. The semiconductor memory device according to claim 1 , further comprising:

a bit line electrically connected to a second end of the memory cell,

wherein the read operation is performed during a write operation as a verify operation that precedes a program operation.

5. The semiconductor memory device according to claim 1 , further comprising:

other memory cells each having a gate electrically connected to the word line and a first end electrically connected to the source line; and

a plurality of bit lines, each of the bit lines connected to a second end of one of the memory cells,

wherein the read operation is performed on all of the memory cells.

6. The semiconductor memory device according to claim 1 , further comprising:

other memory cells each having a gate electrically connected to the word line and a first end electrically connected to the source line; and

a plurality of bit lines, each of the bit lines connected to a second end of one of the memory cells,

wherein the read operation is performed on the memory cells that are electrically connected to every other one of the bit lines.

7. The semiconductor memory device according to claim 1 ,

wherein the second voltage is lower than the first voltage when the second threshold value is greater than the first threshold value, and the second voltage is higher than the first voltage when the second threshold value is less than the first threshold value.

8. The semiconductor memory device according to claim 1 , further comprising:

a bit line;

a first string of memory cells, including the memory cell, that are electrically connected in series between the bit line and the source line;

a first select transistor electrically connected between the bit line and the first string of memory cells;

a second select transistor electrically connected between the bit line and the second string of memory cells;

a first select line electrically connected to a gate of the first select transistor; and

a second select line electrically connected to a gate of the second select transistor,

wherein in the read operation, substantially the same voltage as that applied to the source line is applied to the second select line.

9. A semiconductor memory device comprising:

a memory cell;

a word line electrically connected to a gate of the memory cell;

a source line electrically connected to a first end of the memory cell; and

a control circuit configured to execute a first read operation in response to a first command and a second read operation in response to a second command, wherein

in the first read operation, a first voltage is applied to the source line while a second voltage is applied to the word line to determine whether or not a threshold voltage of the memory cell is above a first threshold value and the first voltage is applied to the source line while a third voltage is applied to the word line to determine whether or not the threshold voltage of the memory cell is above a second threshold value, and

in the second read operation, a fourth voltage is applied to the word line while a fifth voltage is applied to the source line to determine whether or not the threshold voltage of the memory cell is above the first threshold value and the fourth voltage is applied to the word line while a sixth voltage is applied to the source line to determine whether or not the threshold voltage of the memory cell is above the second threshold value.

10. The semiconductor memory device according to claim 9 , wherein a difference between the second and third voltages is equal to a difference between the fifth and sixth voltages.

11. The semiconductor memory device according to claim 9 , wherein a processing time required for the read operation executed in response to the first command is longer than a processing time required for the read operation executed in response to the second command.

12. A semiconductor memory device comprising:

a plurality of memory cells;

a word line electrically connected to a gate of each memory cell; and

a source line electrically connected to a first end of each memory cell,

wherein in a read operation of the memory cell, a first voltage is applied to the source line in a first operation to determine as a first number, the number of memory cells that have threshold voltages above a first threshold value, a second voltage is applied to the source line in a second operation to determine as a second number, the number of memory cells that have threshold voltages above a second threshold value, and a third voltage is applied to the source line in a third operation to determine as a third number, the number of memory cells that have threshold voltages above a third threshold value.

13. The semiconductor memory device according to claim 12 , wherein a fourth voltage is applied to the word line during both the first, second, and third operations.

14. The semiconductor memory device according to claim 13 , wherein the read operation includes a fourth operation in which one of the first, second, and third voltages is applied to the source line to read the value of data stored in the memory cell.

15. The semiconductor memory device according to claim 14 , wherein the first voltage is applied to the source line during the fourth operation when the first number is greater than the second number and the third number.

16. The semiconductor memory device according to claim 12 ,

wherein the second voltage is lower than the first voltage when the second threshold value is greater than the first threshold value, and the second voltage is higher than the first voltage when the second threshold value is less than the first threshold value.

17. The semiconductor memory device according to claim 12 , further comprising:

a plurality of bit lines, each of the bit lines connected to a second end of one of the memory cells,

wherein the read operation is performed on all of the memory cells.

18. The semiconductor memory device according to claim 12 , further comprising:

a plurality of bit lines, each of the bit lines connected to a second end of one of the memory cells,

wherein the read operation is performed on the memory cells that are electrically connected to every other one of the bit lines.