NAND flash memory device capable of selectively erasing one flash memory cell and operation method thereof
View Patent ↗A flash memory device includes a cell array and a control circuit. The cell array includes a first NAND string having first flash memory cells having control gates respectively connected to word lines, and a first bit line selection switch connecting the first flash memory cells to a first bit line according to a control of a first string selection line. The control circuit controls a first erase operation for erasing a selected flash memory cell. The control circuit controls a voltage difference between the first bit line and the first string selection line to have a first value for generating gate induced drain leakage (GIDL) at the first bit line selection switch, and controls a voltage of a control gate of the selected flash memory cell and a voltage of a control gate of an unselected flash memory cell to be different from each other.
1. A flash memory device comprising:
a cell array including a first NAND string having a plurality of first flash memory cells having control gates connected to a plurality of word lines, respectively, and a first bit line selection switch connecting the plurality of first flash memory cells to a first bit line according to a control of a first string selection line; and
a control circuit configured to control a first erase operation for erasing a selected flash memory cell among the plurality of first memory cells,
wherein the control circuit controls a voltage difference between the first bit line and the first string selection line to have a first value for generating gate induced drain leakage (GIDL) at the first bit line selection switch, and controls a voltage of a control gate of the selected flash memory cell and a voltage of a control gate of an unselected flash memory cell among the plurality of first flash memory cells to be different from each other,
wherein the cell array further comprises a second NAND string having a plurality of second flash memory cells having control gates connected to the plurality of word lines, respectively, and a second bit line selection switch connecting the plurality of second flash memory cells to the first bit line according to a control of a second string selection line, and
wherein the control circuit controls a voltage difference between the first bit line and the second string selection line to have a second value that is smaller than the first value during the first erase operation.
2. The flash memory device of claim 1 , wherein the cell array further comprises a third NAND string having a plurality of third flash memory cells having control gates connected to the plurality of word lines, respectively, and a third bit line selection switch connecting the plurality of third flash memory cells to a second bit line according to the control of the first string selection line,
wherein the control circuit controls a voltage difference between the second bit line and the first string selection line to have a third value that is smaller than the first value during the first erase operation.
3. The flash memory device of claim 2 , wherein the cell array further comprises a fourth NAND string having a plurality of fourth flash memory cells having control gates connected to the plurality of word lines, respectively, and a fourth bit line selection switch connecting the plurality of fourth flash memory cells to the second bit line according to the control of the second string selection line,
wherein the control circuit controls a voltage difference between the second bit line and the second string selection line to have a fourth value that is smaller than the first value during the first erase operation.
4. The flash memory device of claim 2 , wherein the control circuit controls a voltage of the second bit line to be smaller than a voltage of the first bit line during the first erase operation.
5. The flash memory device of claim 2 , wherein the control circuit controls a voltage of the second bit line to be smaller than a voltage of the first bit line and to be greater than a voltage of the first string selection line.
6. The flash memory device of claim 2 , wherein the first NAND string further includes a first source line selection switch connecting the plurality of first flash memory cells to the source line according to a control of a source selection line, and
wherein the second NAND string further includes a second source line selection switch connecting the plurality of second flash memory cells to the source line according to the control of the source selection line,
wherein the third NAND string further includes a third source line selection switch connecting the plurality of third flash memory cells to the source line according to the control of the source selection line, and
wherein the control circuit controls a voltage difference between the source selection line and the source line to have a seventh value that is smaller than the first value.
7. The flash memory device of claim 6 , wherein the control circuit further performs a second erase operation to erase all of the plurality of first flash memory cells, the plurality of second flash memory cells, and the plurality of third flash memory cells, and
wherein in the second erase operation, the control circuit controls a voltage difference between the source selection line and the source line to have the first value or a value for generating GIDL at the first source line selection switch, the second source line selection switch, and the third source line selection switch, and controls voltages of control gates of the plurality of first flash memory cells, the plurality of second flash memory cells, and the plurality of third flash memory cells to have a voltage level for erasing the plurality of first flash memory cells, the plurality of second flash memory cells, and the plurality of third flash memory cells.
8. The flash memory device of claim 3 , wherein the first NAND string further includes a first source line selection switch connecting the plurality of first flash memory cells to the source line according to a control of a source selection line,
wherein the second NAND string further includes a second source line selection switch connecting the plurality of second flash memory cells to the source line according to the control of the source selection line,
wherein the third NAND string further includes a third source line selection switch connecting the plurality of third flash memory cells to the source line according to the control of the source selection line,
wherein the fourth NAND string further includes a fourth source line selection switch connecting the plurality of fourth flash memory cells to the source line according to the control of the source selection line, and
wherein the control circuit controls a voltage difference between the source selection line and the source line to have an eighth value that is smaller than the first value.
9. The flash memory device of claim 8 , wherein the control circuit further performs a second erase operation to erase all of the plurality of first flash memory cells, the plurality of second flash memory cells, the plurality of third flash memory cells, and the plurality of fourth memory cells, and
wherein in the second erase operation, the control circuit controls a voltage difference between the source selection line and the source line to have the first value or a value for generating GIDL at the first source line selection switch, the second source line selection switch, the third source line selection switch, and the fourth source line selection switch, and controls voltages of control gates of the plurality of first flash memory cells, the plurality of second flash memory cells, the plurality of third flash memory cells, and the plurality of fourth flash memory cells to have a voltage level for erasing the plurality of first flash memory cells, the plurality of second flash memory cells, the plurality of third flash memory cells, and the plurality of fourth flash memory cells.
10. The flash memory device of claim 1 , wherein the control circuit controls a voltage of the second string selection line to be smaller than a voltage of the first bit line and to be greater than a voltage of the first string selection line.
11. The flash memory device of claim 1 , wherein the first NAND string further includes a first source line selection switch configured to connect the plurality of first flash memory cells to a source line according to a control of a source selection line,
wherein the control circuit controls a voltage difference between the source selection line and the source line to have a fifth value that is smaller than the first value.
12. The flash memory device of claim 11 , wherein the control circuit further performs a second erase operation to erase all of the plurality of first flash memory cells, and
wherein in the second erase operation, the control circuit controls a voltage difference between the source selection line and the source line to have the first value or a value for generating GIDL at the first source line selection switch, and controls voltages of control gates of the plurality of first flash memory cells to have a voltage level for erasing the plurality of first flash memory cells.
13. The flash memory device of claim 1 , wherein the first NAND string further includes a first source line selection switch connecting the plurality of first flash memory cells to the source line according to a control of a source selection line and the second NAND string further includes a second source line selection switch connecting the plurality of second flash memory cells to the source line according to the control of the source selection line,
wherein the control circuit controls a voltage difference between the source selection line and the source line to have a sixth value that is smaller than the first value.
14. The flash memory device of claim 13 , wherein the control circuit further performs a second erase operation to erase all of the plurality of first flash memory cells and the plurality of second flash memory cells, and
wherein in the second erase operation, the control circuit controls a voltage difference between the source selection line and the source line to have the first value or a value for generating GIDL at the first source line selection switch and the second source line selection switch, and controls voltages of control gates of the plurality of first flash memory cells and the plurality of second flash memory cells to have a voltage level for erasing the plurality of first flash memory cells and the plurality of second flash memory cells.
15. The flash memory device of claim 1 , wherein the control circuit performs the first erase operation on the selected flash memory cell when a threshold voltage of the selected flash memory cell is greater than an upper limit and performs a write operation on the selected flash memory cell when the threshold voltage of the selected flash memory cell is smaller than a lower limit.
16. The flash memory device of claim 1 , wherein the control circuit controls a voltage of a control gate of the selected flash memory cell to be lower than a voltage of a control gate of an unselected flash memory cell.
17. The flash memory device of claim 1 , wherein the cell array further includes a plurality of switches configured to connect the plurality of word lines with control gates of the plurality of first flash memory cells,
wherein the control circuit controls the plurality of switches so that a control gate of a flash memory cell other than the selected flash memory cell be separated from a corresponding word line.
18. The flash memory device of claim 1 , wherein the cell array further includes a plurality of switches configured to connect the plurality of word lines to control gates of the plurality of first flash memory cells,
wherein the control circuit controls the plurality of switches so that control gates of the selected flash memory cell and one or more unselected flash memory cells adjacent to the selected flash memory cell be connected to corresponding word lines among the plurality of word lines,
wherein the control circuit controls the plurality of switches so that a control gate of an unselected flash memory cell, other than the selected flash memory cell and the one or more unselected flash memory cells, be separated from a corresponding word line among the plurality of word lines, and
wherein the control circuit controls a voltage of a control gate of the selected flash memory cell to be different from voltages of control gates of the one or more unselected flash memory cells.
19. An operation method of the flash memory device according to claim 1 , the method comprising:
reading a threshold voltage of a selected flash memory cell included in a NAND string of the flash memory device;
erasing the selected flash memory cell when the threshold voltage is greater than an upper limit; and
writing the selected flash memory cell when the threshold voltage is smaller than a lower limit.
20. The operation method of claim 19 , wherein the upper limit and the lower limit respectively correspond to an upper limit and a lower limit of desired threshold voltage distribution corresponding to a data level of the selected flash memory cell.
21. An operation method of the flash memory device according to claim 1 , the method comprising:
writing a selected flash memory cell included in a NAND string of the flash memory device when changing data of the selected flash memory cell into first data; and
erasing the selected flash memory cell when changing data of the selected flash memory cell into second data.
22. The operation method of claim 21 , further comprising:
finding a target flash memory cell where an error occurs in data read from the flash memory device; and
designating the target flash memory cell as the selected flash memory cell.
23. An operation method of the flash memory device according to claim 1 , the method comprising:
reading a turn-on current flowing through a selected flash memory cell among a plurality of flash memory cells included in a NAND string of the flash memory device; and
comparing the turn-on current with a threshold value and erasing or writing the selected flash memory cell according to a comparison result.
24. The operation method of claim 23 , further comprising writing all of the plurality of flash memory cells included in the NAND string.
25. An operation method of a flash memory device, the method comprising:
writing a selected flash memory cell included in a NAND string of the flash memory device when changing data of the selected flash memory cell into first data;
erasing the selected flash memory cell when changing data of the selected flash memory cell into second data;
finding a target flash memory cell corresponding to a synapse weight to be changed among synapse weights of a neural network stored in the flash memory device; and
designating the flash memory cell as the selected flash memory cell.
26. An operation method of a flash memory device, the method comprising:
writing a predetermined number of flash memory cells included in a block, the block including a plurality of NAND strings each including a plurality of flash memory cells;
reading a threshold voltage of a selected flash memory cell among the predetermined flash memory cells; and
comparing the threshold voltage of the selected flash memory cell with an upper limit and a lower limit;
writing the selected flash memory cell when the threshold voltage of the selected flash memory cell is smaller than the lower limit; and
erasing the selected flash memory cell when the threshold voltage of the selected flash memory cell is greater than the upper limit.
27. The operation method of claim 26 , wherein the predetermined number of flash memory cells correspond to all flash memory cells included in the block.
28. The operation method of claim 26 , wherein the predetermined number of flash memory cells correspond to a plurality of flash memory cells connected to a selected word line among a plurality of word lines.
29. The operation method of claim 26 , wherein writing the predetermined number of flash memory cells includes providing a voltage for a write operation to a word line connected with the predetermined number of flash memory cells; and connecting at least one of a bit line or a source line to the predetermined number of flash memory cells so that carriers are provided to channels of the predetermined number of flash memory cells.