Scheme for page erase and erase verify in a non-volatile memory array

• US 5,995,417 A
• Filed: 10/20/1998
• Issued: 11/30/1999
• Est. Priority Date: 10/20/1998
• Status: Expired due to Term

• Current Assignee: Valley Device Management
• Original Assignee: Advanced Micro Devices, Inc.
• Inventors: Leung, Vincent, Yano, Masaru, Le, Binh Quang, Chen, Pau-Ling, Chung, Michael S. C., Hollmer, Shane C.
• Primary Examiner(s): PHAN, TRONG Q
• Application Number:
  US09/175,646
• Time in Patent Office: 406 Days
• Field of Search: 365/185.12, 365/185.13, 365/185.17, 365/185.18, 365/185.22, 365/185.23, 365/185.27, 365/185.29, 365/185.33, 365/218
• US Class Current: 365/185.29
• CPC Class Codes: G11C 16/16 for erasing blocks, e.g. arrays, words, groups
• CPC Class Codes: G11C 16/344 Arrangements for verifying correct erasure or for detecting overerased cells
• CPC Class Codes: G11C 16/3445 Circuits or methods to verify correct erasure of nonvolatile memory cells

Abstract

A non-volatile memory device includes a plurality of MOS transistors 34 and 36 connected to respective word lines 16 and 18 to allow individual pages of memory stored in the memory cells 8a, 10a and 8b, 10b on the respective word lines 16 and 18 to be erased and erase verified. A method of erasing a page of memory cells includes the steps of applying an erase voltage to one of the MOS transistors 16 and 18 to erase the page of memory cells along the respective word line, and applying an initial erase-inhibit floating voltage to other MOS transistors which are connected to the word lines unselected for page erase. In an erase verify mode, an erase verify voltage is applied to the word line which was selected for page erase in the erase mode, and an erase verify unselect voltage is applied to the word lines which was not selected for page erase.

Claims

1. A non-volatile memory device, comprising:

(a) a semiconductor substrate capable of being applied of first substrate voltage to set the memory device in an erase mode;

(b) an array of memory cells arranged in a plurality of rows on the substrate, each of the memory cells capable of storing a respective bit;

(c) a plurality of word lines each connected to a respective one of the rows of the memory cells;

(d) a plurality of metal oxide semiconductor (MOS) transistors each connected to a respective one of the word lines, wherein the MOS transistors comprise respective gates, each of the word lines in the erase mode capable of receiving an erase voltage to erase the bits stored in the memory cells on the word line if it is selected for page erase and an initial erase-inhibit floating voltage to maintain the bits stored in the memory cells on the word line if it is unselected for page erase; and

(e) a word line pump connected to provide a first gate turn-on voltage to the gates of the MOS transistors.

2. The non-volatile memory device of claim 1, further comprising an X-decoder connected to the word line pump.

3. The non-volatile memory device of claim 1, wherein the substrate is further capable of being applied a second substrate voltage to set the memory device in an erase-verify mode, and wherein each of the MOS transistors in the erase verify mode is capable of receiving an erase verify voltage to verify whether the memory cells on the word line have been erased if it was selected for page erase in the erase mode and erase verify unselect voltage to unselect the word line for erase verify if it was unselected for page erase in the erase mode.

4. The non-volatile memory device of claim 3, wherein the erase verify voltage is on the order of about 0 V.

5. The non-volatile memory device of claim 3, wherein the erase verify unselect voltage is on the order of about 4.5 V.

6. The non-volatile memory device of claim 3, wherein the MOS transistors comprise respective gates, further comprising a word line pump connected to provide a second gate turn-on voltage to the gates of the MOS transistor.

7. The non-volatile memory device of claim 6, wherein the second gate turn-on voltage is in the range of about 7 V to about 8 V in the erase verify mode.

8. A non-volatile memory device, comprising:

(a) a semiconductor substrate capable of being applied a first substrate voltage to set the memory device in an erase mode;

(b) an array of memory cells arranged in a plurality of rows on the substrate, each of the memory cells capable of storing a respective bit;

(c) a plurality of word lines each connected to a respective one of the rows of the memory cells;

(d) a plurality of metal oxide semiconductor (MOS) transistors each connected to a respective one of the word lines, each of the word lines in the erase mode capable of receiving an erase voltage to erase the bits stored in the memory cells on the word line if it is selected for page erase and an initial erase-inhibit floating voltage to maintain the bits stored in the memory cells on the word line if it is unselected for page erase; and

(e) a plurality of select source and select drain devices comprising a plurality of gates connected to the array of memory cells, the gates of the select drain devices and select source devices capable of receiving a voltage on the order of about 4.5 V in the erase verify mode.

9. A method of erasing a page of memory in a non-volatile memory device comprising a plurality of memory cells arranged in a plurality of sectors, each of the sectors comprising a plurality of word lines each connected to a respective one of a plurality of rows of the memory cells, the method comprising the steps of:

(a) apply an erase voltage to a selected one of the word lines to erase a selected page of memory on the selected word line;

(b) apply an initial erase-inhibit floating voltage to an unselected one of the word lines to maintain a page of memory unselected for page erase on the unselected word line;

(c) applying an erase verify voltage to the selected word line subsequent to the step of applying the erase voltage to the selected word line to verify that the selected page of memory was erased; and

(d) applying an erase verify unselect voltage to the unselected word line subsequent to the step of applying the initial erase-inhibit floating voltage to the unselected word line to avoid erase verifying the unselected page of memory which was erase-inhibited.

10. The method of claim 9, wherein the erase verify voltage applied to the selected word line is on the order of about 0 V.

11. The method of claim 9, wherein the erase verify unselect voltage applied to the unselected word line is on the order of about 4.5 V.

12. The method of claim 9, wherein the non-volatile memory device further comprises a plurality of n-channel MOS (NMOS) transistors including a first NMOS transistor connected to the selected word line and a second NMOS transistor connected to the unselected word line, each of the NMOS transistors comprising a source, a drain and a gate, wherein the step of applying the erase verify voltage comprises the step of applying the erase verify voltage to the drain of the first NMOS transistor, and wherein the step of applying the erase verify unselect voltage comprises the step of applying the erase verify unselect voltage to the drain of the second NMOS transistor.

13. A method of erasing and erase-verifying a page of memory in a non-volatile memory device comprising a plurality of memory cells arranged in a plurality of sectors, each of the sectors comprising a plurality of word lines each connected to a respective one of a plurality of rows of the memory cells, each of the word lines coupled to a respective one of a plurality of metal oxide semiconductor (MOS) transistors each comprising a gate, a source and a drain, the method comprising the steps of:

(a) applying an erase voltage to a selected one of the MOS transistors to erase a selected page of memory on a selected one of the word lines to which the selected MOS transistor is connected;

(b) applying an initial erase-inhibit floating voltage to an unselected one of the MOS transistors to maintain an unselected page of memory on an unselected one of the word lines to which the unselected MOS transistor is connected;

(c) applying an erase verify voltage to the selected MOS transistor subsequent to the step of applying the erase voltage to the selected MOS transistor to verify that the selected page of memory was erased; and

(d) applying an erase verify unselect voltage to the unselected MOS transistor subsequent to the step of applying the initial erase-inhibit floating voltage to the unselected MOS transistor to avoid erase verifying the unselected page of memory which was erase-inhibited.

14. The method of claim 13, wherein the erase voltage applied to the selected MOS transistor is on the order of about 0 V.

15. The method of claim 13, wherein the initial erase-inhibit floating voltage applied to the selected MOS transistor is 1.7 V to about 2.3 V.

16. The method of claim 13, wherein the MOS transistors comprise n-channel MOS (NMOS) transistors, wherein the step of applying the erase voltage comprises the step of applying the erase voltage to the drain of the selected NMOS transistor, wherein the step of applying the initial erase-inhibit floating voltage comprises the step of applying the initial erase-inhibit floating voltage to the drain of the unselected NMOS transistor, wherein the step of applying the erase verify voltage comprises the step of applying the erase verify voltage to the drain of the selected NMOS transistor, and wherein the step of applying the erase verify unselect voltage comprises the step of applying the erase verify unselect voltage to the drain of the unselected NMOS transistor.

17. The method of claim 13, further comprising the step of applying a first gate turn-on voltage in the range of about 2.7 V to about 3.3 V to the gates of the NMOS transistors during steps (a) and (b).

18. The method of claim 17, further comprising the step of applying a second turn-on voltage in the range of about 7 V to about 8 V to the gates of the NMOS transistors during steps (c) and (d).

19. The method of claim 13, wherein the memory cells are disposed on a semiconductor substrate, further comprising the step of applying a first substrate voltage on the order of about 20 V to the substrate prior to the steps of applying the erase verify voltage to the selected MOS transistor and the erase verify unselect voltage to the unselected MOS transistor.

20. The method of claim 19, wherein the substrate comprises a p-well, and wherein the step of applying the first substrate voltage to the substrate comprises the step of applying the first substrate voltage to the p-well.

21. The method of claim 19, wherein the unselected word line is coupled up to the substrate voltage in response to the step of applying the substrate voltage of about 20 V to the substrate.

22. The method of claim 19, further comprising the step of applying a second substrate voltage of about 0 V to the substrate during the steps of applying the erase verify voltage to the selected MOS transistor and the erase verify unselect voltage to the unselected MOS transistor.

23. The method of claim 22, wherein the substrate comprises a p-well, and wherein the step of applying the second substrate voltage to the substrate comprises the step of applying the second substrate voltage to the p-well.

24. The method of claim 13, wherein the erase verify voltage applied to the selected MOS transistor is on the order of about 0 V.

25. The method of claim 13, wherein the erase verify unselect voltage applied to the unselected MOS transistor is on the order of about 4.5 V.

26. The method of claim 13, wherein the memory cells are connected to a plurality of select source devices comprising a plurality of gates, further comprising the step of applying a source voltage on the order of about 4.5 V to the gates of the select source devices during the steps of applying the erase verify voltage to the selected MOS transistor and the erase verify unselect voltage to the unselected MOS transistor.

27. The method of claim 13, wherein the memory cells are further connected to a plurality of select drain devices comprising a plurality of gates, further comprising the step of applying a drain voltage on the order of about 4.5 V to the gates of the select drain devices during the steps of applying the erase verify voltage to the selected MOS transistor and the erase verify unselect voltage to the unselected MOS transistor.

28. The method of claim 26, wherein the select source devices are connected to an array ground, further comprising the step of applying an array ground voltage on the order of about 0.7 V to the array ground during steps (c) and (d).

29. A method of erasing and erase-verifying a page of memory in a non-volatile memory device comprising a plurality of memory cells arranged in a plurality of sectors, each of the sectors comprising a plurality of word lines each connected to a respective one of a plurality of rows of the memory cells, each of the word lines coupled to a respective one of a plurality of metal oxide semiconductor (MOS) transistors each comprising a gate, a source and a drain, the method comprising the steps of:

(a) applying an erase voltage on the order of about 0 V to a selected one of the MOS transistors to erase a selected page of memory on a selected one of the word lines to which the selected MOS transistor is connected;

(b) applying an initial erase-inhibit floating voltage in the range of about 2.7 V to about 3.3 V to an unselected one of the MOS transistors to maintain an unselected page of memory on an unselected one of the word lines to which the unselected MOS transistor is connected;

(c) applying an erase verify voltage on the order of about 0 V to the selected MOS transistor subsequent to the step of applying the erase voltage to the selected MOS transistor to verify that the selected page of memory was erased; and

(d) applying an erase verify unselect voltage on the order of about 4.5 V to the unselected MOS transistor subsequent to the step of applying the initial erase-inhibit floating voltage to the unselected MOS transistor to avoid erase verifying the unselected page of memory which was erase-inhibited.

30. The method of claim 29, wherein the MOS transistors comprise n-channel MOS (NMOS) transistors, wherein the step of applying the erase voltage comprises the step of applying the erase voltage to the drain of the selected NMOS transistor, wherein the step of applying the initial erase-inhibit floating voltage comprises the step of applying the initial erase-inhibit floating voltage to the drain of the unselected NMOS transistor, wherein the step of applying the erase verify voltage comprises the step of applying the erase verify voltage to the drain of the selected NMOS transistor, and wherein the step of applying the erase verify unselect voltage comprises the step of applying the erase verify unselect voltage to the drain of the unselected NMOS transistor.

31. The method of claim 29, further comprising the step of applying a first gate turn-on voltage in the range of about 2.7 V to about 3.3 V to the gates of the NMOS transistors during steps (a) and (b).

32. The method of claim 31, further comprising the step of applying a second turn-on voltage in the range of about 7 V to about 8 V to the gates of the NMOS transistors during steps (c) and (d).

33. The method of claim 29, wherein the memory cells are disposed on a semiconductor substrate, further comprising the step of applying a first substrate voltage on the order of about 20 V to the substrate prior to the steps of applying the erase verify voltage to the selected MOS transistor and the erase verify unselect voltage to the unselected MOS transistor.

34. The method of claim 33, wherein the substrate comprises a p-well, and wherein the step of applying the first substrate voltage to the substrate comprises the step of applying the first substrate voltage to the p-well.

35. The method of claim 33, wherein the unselected word line is coupled up to the substrate voltage in response to the step of applying the substrate voltage of about 20 V to the substrate.

36. The method of claim 33, further comprising the step of applying a second substrate voltage of about 0 V to the substrate during the steps of applying the erase verify voltage to the selected MOS transistor and the erase verify unselect voltage to the unselected MOS transistor.

37. The method of claim 36, wherein the substrate comprises a p-well, and wherein the step of applying the second substrate voltage to the substrate comprises the step of applying the second substrate voltage to the p-well.

38. The method of claim 29, wherein the memory cells are connected to a plurality of select source devices comprising a plurality of gates, further comprising the step of applying a source voltage on the order of about 4.5 V to the gates of the select source devices during the steps of applying the erase verify voltage to the selected MOS transistor and the erase verify unselect voltage to the unselected MOS transistor.

39. The method of claim 29, wherein the memory cells are further connected to a plurality of select drain devices comprising a plurality of gates, further comprising the step of applying a drain voltage on the order of about 4.5 V to the gates of the select drain devices during the steps of applying the erase verify voltage to the selected MOS transistor and the erase verify unselect voltage to the unselected MOS transistor.

40. The method of claim 38, wherein the selected source devices are connected to an array ground, further comprising the step of applying an array ground voltage on the order of about 0.7 V to the array ground during steps (c) and (d).

41. A method of erasing and erase-verifying a page of memory in a non-volatile memory device comprising a plurality of memory cells arranged in a plurality of sectors on a semiconductor substrate, each of the sectors comprising a plurality of word lines each connected to a respective one of a plurality of rows of the memory cells, each of the word lines coupled to a respective one of a plurality of metal oxide semiconductor (MOS) transistors each comprising a gate, a source and a drain, the method comprising the steps of:

(a) applying an erase voltage to a first one of the MOS transistors to erase a first page of memory on a respective first one of the word lines to which the first MOS transistor is connected;

(b) applying an initial erase-inhibit floating voltage to a second one of the MOS transistors to maintain a second page of memory on a respective second one of the word lines to which the second MOS transistor is connected;

(c) applying a first substrate voltage on the order of about 20 V to the substrate during the steps of applying the erase voltage to the first MOS transistor and the initial erase-inhibit floating voltage to the second MOS transistor;

(d) applying an erase verify voltage to the first MOS transistor subsequent to the step of applying the erase voltage to the first MOS transistor to verify that the first page of memory has been erased;

(e) applying an erase verify unselect voltage to the second MOS transistor subsequent to the step of applying the initial erase-inhibit floating voltage to the second MOS transistor to unselect for erase verify the second page of memory which has been erase-inhibited; and

(f) applying a second substrate voltage of about 0 V to the substrate during the steps of applying the erase verify voltage to the first MOS transistor and the erase verify unselect voltage to the second MOS transistor.

42. The method of claim 41, wherein the erase voltage applied to the first MOS transistor is on the order of about 0 V.

43. The method of claim 41, wherein the initial erase-inhibit floating voltage applied to the second MOS transistor is in the range of about 1.7 V to about 2.3 V.

44. The method of claim 41, wherein the MOS transistors comprise n-channel MOS (NMOS) transistors, wherein the step of applying the erase voltage comprises the step of applying the erase voltage to the drain of the first NMOS transistor, wherein the step of applying the initial erase-inhibit floating voltage comprises the step of applying the initial erase-inhibit floating voltage to the drain of the second NMOS transistor, wherein the step of applying the erase verify voltage comprises the step of applying the erase verify voltage to the drain of the first NMOS transistor, and wherein the step of applying the erase verify unselect voltage comprises the step of applying the erase verify unselect voltage to the drain of the second NMOS transistor.

45. The method of claim 41, further comprising the step of applying a first gate turn-on voltage in the range of about 2.7 V to 3.3 V to the gates of the MOS transistors during steps (a) and (b).

46. The method of claim 45, further comprising the step of applying a second turn-on voltage in the range of about 7 V to about 8 V to the gates of the NMOS transistors during steps (d) and (e).

47. The method of claim 41, wherein the substrate comprises a p-well, wherein the step of applying the first substrate voltage to the substrate comprises the step of applying the first substrate voltage to the p-well, and wherein the step of applying the second substrate voltage to the substrate comprises the step of applying the second substrate voltage to the p-well.

48. The method of claim 41, wherein the erase verify voltage applied to the first MOS transistor is on the order of about 0 V.

49. The method of claim 41, wherein the erase verify unselect voltage applied to the second MOS transistor is on the order of about 4.5 V.

50. The method of claim 41, wherein the memory cells are connected to a plurality of select source devices and select drain devices comprising a plurality of gates, further comprising the step of applying a voltage on the order of about 4.5 V to the gates of the select source devices and select drain devices during the steps of applying the erase verify voltage to the first MOS transistor and the erase verify unselect voltage to the second MOS transistor.

51. The method of claim 41, wherein the memory cells are connected to a plurality of select source devices comprising a plurality of gates, further comprising the step of applying a source voltage on the order of about 4.5 V to the gates of the select source devices during the steps of applying the erase verify voltage to the selected MOS transistor and the erase verify unselect voltage to the unselected MOS transistor during steps (d) and (e).

52. A method of erasing and erase-verifying a page of memory in a non-volatile memory device comprising a plurality of memory cells arranged in a plurality of sectors on a semiconductor substrate, each of the sectors comprising a plurality of word lines each connected to a respective one of a plurality of rows of the memory cells, each of the word lines coupled to a respective one of a plurality of metal oxide semiconductor (MOS) transistors each comprising a gate, a source and a drain, the memory cells connected to a plurality of select source gates, a plurality of select drain gates and an array ground, the method comprising the steps of:

(a) applying an erase voltage on the order of about 0 V to a first one of the MOS transistors to erase a first page of memory on a respective first one of the word lines to which the first MOS transistor is connected;

(b) applying an initial erase-inhibit floating voltage in the range of about 1.7 V to about 2.3 V to a second one of the MOS transistors to maintain a second page of memory on a respective second one of the word lines to which the second MOS transistor is connected;

(c) applying a first substrate voltage on the order of about 20 V to the substrate during the steps of applying the erase voltage to the first MOS transistor and the initial erase-inhibit floating voltage to the second MOS transistor;

(d) applying an erase verify voltage on the order of about 0 V to the first MOS transistor subsequent to the step of applying the erase voltage to the first MOS transistor to verify that the first page of memory has been erased;

(e) applying an erase verify unselect voltage on the order of about 4.5 V to the second MOS transistor subsequent to the step of applying the initial erase-inhibit floating voltage to the second MOS transistor to unselect for erase verify the second page of memory which has been erase-inhibited;

(f) applying a second substrate voltage of about 0 V to the substrate during the steps of applying the erase verify voltage to the first MOS transistor and the erase verify unselect voltage to the second MOS transistor;

(g) applying an array ground voltage on the order of about 0.7 V to the array ground during the steps of applying the erase verify voltage to the first MOS transistor and the erase verify unselect voltage to the second MOS transistor; and

(h) applying a voltage on the order of about 4.5 V to the select drain gates and select source gates during the steps of applying the erase verify voltage to the first MOS transistor and the erase verify unselect voltage to the second MOS transistor.

53. The method of claim 52, wherein the MOS transistors comprise n-channel MOS (NMOS) transistors, wherein the step of applying the erase voltage comprises the step of applying the erase voltage to the drain of the first NMOS transistor, wherein the step of applying the initial erase-inhibit floating voltage comprises the step of applying the initial erase-inhibit floating voltage to the drain of the second NMOS transistor, wherein the step of applying the erase verify voltage comprises the step of applying the erase verify voltage to the drain of the first NMOS transistor, and wherein the step of applying the erase verify unselect voltage comprises the step of applying the erase verify unselect voltage to the drain of the second NMOS transistor.

54. The method of claim 52, further comprising the step of applying a first gate turn-on voltage in the range of about 2.7 V to about 3.3 V to the gates of the MOS transistors during steps (a) and (b).

55. The method of claim 54, wherein the memory cells are connected to a plurality of select source devices comprising a plurality of gates, further comprising the step of applying a source voltage on the order of about 4.5 V to the gates of the select source devices during the steps of applying the erase verify voltage to the selected MOS transistor and the erase verify unselect voltage to the unselected MOS transistor during steps (d) and (e).

56. The method of claim 52, wherein the substrate comprises a p-well, wherein the step of applying the first substrate voltage to the substrate comprises the step of applying the first substrate voltage to the p-well, and wherein the step of applying the second substrate voltage to the substrate comprises the step of applying the second substrate voltage to the p-well.