Granted Patent B2

US 10,109,356 · App. 14/631,365 · Granted Oct 23, 2018

Abstract

Claims (54)

1. A method for stressing a plurality of non-volatile memory cells, the method comprising:

entering an erase stress mode of the plurality of non-volatile memory cells;

during the erase stress mode:

providing one or more erase stress pulses to the plurality of non-volatile memory cells; and

determining that a threshold voltage of a predetermined plurality of non-volatile memory cells has a first relationship that is either greater than or less than a first predetermined voltage, the first predetermined voltage being substantially less than a normal erase verify voltage, wherein the threshold voltage is lower than the normal erase verify voltage during the erase stress mode;

entering a recovery period of program stressing of the plurality of non-volatile memory cells in response to determining that the threshold voltage of the predetermined non-volatile memory cells has the first relationship with the predetermined voltage;

during the recovery period of program stressing:

providing one or more program stress pulses to the plurality of memory cells; and

determining that the threshold voltage of at least a subset of the plurality of memory cells has a second relationship with the first predetermined voltage that is different than the first relationship, wherein the threshold voltage is lower than the normal erase verify voltage during the recovery period;

determining whether a predetermined amount of erase stress and program stress has been reached in response to determining that the threshold voltage of the predetermined non-volatile memory cells has the second relationship with the predetermined voltage;

entering the erase stress mode of the plurality of non-volatile memory cells in response to determining that the predetermined amount of erase stress and program stress has not been reached;

during the erase stress mode:

providing one or more erase stress pulses to the plurality of non-volatile memory cells.

2. The method of claim 1 , wherein determining that a threshold voltage of the predetermined plurality of non-volatile memory cells has a first relationship further comprising determining that the first relationship is less than the first predetermined voltage.

3. The method of claim 2 , further comprising determining that the threshold voltage is not less than the first predetermined voltage, and in response, providing additional erase stress pulses to the plurality of non-volatile memory cells.

4. The method of claim 1 , wherein determining that the threshold voltage of the predetermined plurality of memory cells has a second relationship further comprising determining that the second relationship is greater than the first predetermined voltage.

5. The method of claim 4 , further comprising determining that the threshold voltage is not greater than the first predetermined voltage, and in response, providing additional program stress pulses to the plurality of non-volatile memory cells.

6. The method of claim 1 , further comprising setting a maximum number of erase stress pulses and a maximum number of program stress pulses to be applied to the plurality of memory cells.

7. The method of claim 1 , wherein providing one or more erase stress pulses to the plurality of memory cells further comprises providing one or more erase stress pulses with a predetermined duration such that an electric field of the plurality of non-volatile memory cells is below a dielectric conduction electric field of an insulating layer between a control gate and a charge storage layer of the plurality of non-volatile memory cells.

8. The method of claim 1 , wherein providing one or more erase stress pulses comprises providing a negative voltage to a control gate that has a magnitude greater than a magnitude of a normal erase voltage, providing a positive voltage to a well terminal that has a magnitude greater than a magnitude of the normal erase voltage, and floating the source and drain terminals, and wherein providing one or more program stress pulses comprises providing a first positive voltage to the control gate, providing a second positive voltage to the drain terminal, and coupling both the source terminal and the well terminal to ground.

9. The method of claim 1 , wherein each erase stress pulse of the one or more erase stress pulses to the plurality of memory cells comprises:

providing −8.5 volts to control gates of the plurality of memory cells; and

providing 9.5 volts to wells of the plurality of memory cells.

10. The method of claim 9 , wherein each one of the program stress pulses of the one or more program stress pulses to the plurality of memory cells comprises:

providing 3 volts to the control gates of the plurality of memory cells;

providing 4.2 volts to drain nodes of the plurality of memory cells; and

providing 0 volts to the wells of the plurality of memory cells.

11. The method of claim 1 , further comprising:

determining that the threshold voltage of at least a subset of the plurality of memory cells is substantially less than the normal erase verify voltage after the program stress mode.

12. A method for stressing a plurality of non-volatile memory cells, the method comprising:

entering an erase stress mode of the plurality of non-volatile memory cells;

during the erase stress mode:

providing a plurality of erase stress pulses to the plurality of non-volatile memory cells; and

determining that a threshold voltage of a predetermined plurality of non-volatile memory cells has a first relationship that is either greater than or less than a predetermined voltage, the predetermined voltage being substantially less than a normal erase verify voltage, wherein the threshold voltage is lower than the normal erase verify voltage during the erase stress mode;

entering a program stress mode of the plurality of non-volatile memory cells in response to determining that the threshold voltage of the predetermined non-volatile memory cells has the first relationship to the predetermined voltage; and

during the program stress mode:

providing one or more program stress pulses to the plurality of memory cells;

determining that the threshold voltage of the predetermined plurality of memory cells has a second relationship to the predetermined voltage that is different than the first relationship, wherein the threshold voltage is lower than the normal erase verify voltage during a recovery period;

determining whether a predetermined amount of erase stress and program stress has been reached in response to determining that the threshold voltage of the predetermined non-volatile memory cells has the second relationship with the predetermined voltage;

entering the erase stress mode of the plurality of non-volatile memory cells in response to determining that the predetermined amount of erase stress and program stress has not been reached; and

during the erase stress mode:

providing one or more erase stress pulses to the plurality of non-volatile memory cells; and

determining that the threshold voltage of the predetermined plurality of non-volatile memory cells has the first relationship with the first predetermined voltage; and

entering the recovery period of program stressing of the plurality of non-volatile memory cells in response to determining that the threshold voltage of the predetermined non-volatile memory cells has the first relationship with the predetermined voltage.

13. The method of claim 12 , further comprising setting a maximum number of erase stress pulses and a maximum number of program stress pulses to be applied to the plurality of memory cells.

14. The method of claim 12 , wherein determining that a threshold voltage of the predetermined plurality of non-voltage memory cells has a first relationship further comprises determining that the first relationship is less than the predetermined voltage.

15. The method of claim 12 , wherein determining that the threshold voltage of the predetermined plurality of memory cells has a second relationship further comprises determining that the second relationship is greater than the predetermined voltage.

16. The method of claim 12 , wherein each of the plurality of non-volatile memory cells comprises a control gate, a charge storage layer, a source terminal, a drain terminal, and a well terminal.

17. The method of claim 16 , wherein providing one or more erase stress pulses comprises providing a negative voltage to the control gate that has a magnitude greater than a magnitude of a normal erase voltage, providing a positive voltage to the well terminal that has a magnitude greater than a magnitude of the normal erase voltage, and floating the source and drain terminals, and wherein providing one or more program stress pulses comprises providing a first positive voltage to the control gate, providing a second positive voltage to the drain terminal, and coupling the source terminal and the well terminal to ground.

18. A non-volatile memory comprising:

a plurality of non-volatile memory cells; and

a non-volatile memory controller coupled to the plurality of non-volatile memory cells, the non-volatile memory controller having a erase stress mode to stress the plurality of non-volatile memory cells by causing one or more erase stress pulses to be provided to the plurality of memory cells, the memory controller to determine that a threshold voltage of predetermined plurality of non-volatile memory cells has a first relationship that is either greater than or less than a first predetermined voltage, the first predetermined voltage being substantially less than a normal erase verify voltage, wherein the threshold voltage is lower than the normal erase verify voltage during the erase stress mode, the memory controller to enter a program stress mode in response to the threshold voltage of the predetermined plurality of non-volatile memory cells having the first relationship to the first predetermined voltage, to provide one or more program stress pulses to the plurality of memory cells during the program stress mode; and the memory controller to determine that the threshold voltage of at least a subset of the plurality of memory cells has a second relationship to the first predetermined voltage that is different than the first relationship during the program stress mode, wherein the threshold voltage is lower than the normal erase verify voltage during a recovery period, to determine whether a predetermined amount of erase stress and program stress has been reached in response to determining that the threshold voltage of the predetermined non-volatile memory cells has the second relationship with the predetermined voltage, and to entering the erase stress mode of the plurality of non-volatile memory cells in response to determining that the predetermined amount of erase stress and program stress has not been reached.

19. The non-volatile memory of claim 18 , wherein each of the plurality of non-volatile memory cells comprises a control gate, a charge storage layer, a source terminal, a drain terminal, and a well terminal.

20. The non-volatile memory of claim 18 , wherein the one or more erase stress pulses comprises providing a negative voltage to the control gate that has a magnitude greater than a magnitude of a normal erase voltage, providing a positive voltage to well terminal that has a magnitude greater than a magnitude of the normal erase voltage, and floating the source and drain terminals, and wherein the one or more program stress pulses comprises providing a first positive voltage to the control gate, providing a second positive voltage to the drain terminal, and coupling both the source terminal and the well terminal to ground.

Assignments (10)