Resistive memory device and method of operating the resistive memory device

1. A resistive memory device, comprising:

one or more strings respectively coupled between one or more source lines and one or more bit lines, each string including a set of one or more resistive memory cells;

one or more word lines respectively coupled to the set of one or more resistive memory cells; and

a voltage generator configured to control a level of a turn-on voltage to be applied to one or more unselected word lines among the one or more word lines depending on a program target state of a subset of resistive memory cells including one or more resistive memory cells selected from among the set of one or more resistive memory cells.

2. The resistive memory device according to claim 1 , wherein the voltage generator is configured to increase the level of the turn voltage when the program target state rises.

3. The resistive memory device according to claim 2 , wherein the turn-on voltage is set to a positive voltage higher than a ground voltage.

4. The resistive memory device according to claim 1 , wherein the voltage generator is configured to generate a ground voltage to be applied to the one or more source lines and generate a set voltage to be applied to the one or more bit lines.

5. The resistive memory device according to claim 4 , wherein the set voltage is set to a positive voltage higher than the ground voltage.

6. The resistive memory device according to claim 1 , wherein the voltage generator is configured to generate a turn-off voltage to be applied to a selected word line coupled to the one or more selected resistive memory cells included in the subset of resistive memory cells.

7. The resistive memory device according to claim 6 , wherein the turn-off voltage is set to a ground voltage.

8. The resistive memory device according to claim 1 , wherein, when the one or more source lines are respectively coupled to each of the one or more strings, the voltage generator is configured to generate a ground voltage to be applied to the one or more bit lines and to control reset voltages to be applied to the one or more source lines respectively coupled to the one or more strings depending on the program target state.

9. The resistive memory device according to claim 8 , wherein the reset voltages are set to negative voltages lower than the ground voltage.

10. The resistive memory device according to claim 8 , wherein the voltage generator is configured to decrease the levels of the reset voltages when the program target state rises.

11. A method of operating a resistive memory device during a program operation performed on resistive memory cells coupled between one or more source lines and one or more hit lines, the method comprising:

applying a ground voltage to the one or more source lines and applying a set voltage higher than the ground voltage to one or more bit lines selected from among the one or more bit lines;

applying a turn-off voltage to a selected word line coupled to resistive memory cells selected from among the resistive memory cells; and

applying a turn-on voltage, a level of which is controlled depending on a program target state of the selected resistive memory cells, to unselected word lines coupled to unselected resistive memory cells among the resistive memory cells.

12. The method according to claim 11 , wherein the turn-off voltage is set to the ground voltage.

13. The method according to claim 11 , wherein the turn-on voltage is set to a positive voltage higher than the turn-off voltage.

14. The method according to claim 11 , wherein the level of the turn-on voltage is controlled to be higher as the program target state rises.

15. The method according to claim 11 , wherein, when the program operation is performed on the selected resistive memory cells, the turn-off voltage is applied to bit lines coupled to resistive memory cells, the program target state of which is an erased state, or which have been programmed to the program target state.

16. The method according to claim 11 , further comprising:

when resistive memory cells, the program target state of which is a first program state, among the selected resistive memory cells, are programmed to the first program state, programming resistive memory cells, the program target state of which is a second program state, among the resistive memory cells programmed to the first program state.

17. The method according to claim 16 , wherein programming the resistive memory cells, the program target state of which is the second program state, comprises:

applying the ground voltage to unselected bit lines among the one or more bit lines and to the one or more source lines, and applying the set voltage to remaining bit lines other than the unselected bit lines;

applying a turn-off voltage to the selected word line; and

applying a voltage higher than the turn-on voltage to the unselected word lines.

18. A method of operating a resistive memory device, comprising:

applying a ground voltage to selected bit lines and applying reset voltages to selected source lines;

applying a turn-off voltage to a selected word line; and

applying a turn-on voltage to unselected word lines,

wherein the reset voltages are controlled depending on a program target state of selected memory cells coupled to the selected word line.

19. The method according to claim 18 , wherein the level of the reset voltages is set to be higher as the program target state rises.

20. The method according to claim 18 , wherein the reset voltages are set to negative voltages lower than the ground voltage.