POST OVER-ERASE CORRECTION METHOD WITH AUTO-ADJUSTING VERIFICATION AND LEAKAGE DEGREE DETECTION
20220223213 · 2022-07-14
Inventors
Cpc classification
G11C16/345
PHYSICS
G11C16/28
PHYSICS
G11C16/3409
PHYSICS
G11C16/3404
PHYSICS
G11C16/14
PHYSICS
International classification
G11C16/34
PHYSICS
G11C16/14
PHYSICS
Abstract
A post over-erase correction (POEC) method with an auto-adjusting verification mechanism and a leakage degree detection function detects gm degradation or leakage degree of flash cells before or after entering the POEC process. When a preset condition is satisfied, the auto-adjusting verification mechanism of the POEC is switched on to further reduce leakage current. After cycling, the POEC repairs Vt of over-erased cells to a higher level to solve leakage issues. The erase shot count increases due to slower erase speeds after cycling. Therefore, the cycling degree of flash cells is detected by observing the shot number that the erase operation used. When the leakage phenomenon becomes serious, the bit line (BL) leakage current, amount of repaired BLs, and over-erase correction (OEC) shot number will increase during the OEC procedure. Therefore, the leakage degree of flash cells can be detected by inspecting the above data.
Claims
1. A post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function comprising: programming a plurality of flash cells; erasing the plurality of flash cells; performing over-erase correction; determining a target degree to obtain a switch condition result; and turning on the auto-adjusting verification mechanism and performing post over-erase correction based upon the switch condition result; wherein determining the target degree to obtain a switch condition result considers g.sub.m degradation.
2. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 1, wherein reference current is produced by multiple sets of reference cells or constant current and turning on the auto-adjusting verification mechanism reduces an amount of reference cells or constant current to lower reference current.
3. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 1, turning on the auto-adjusting verification mechanism and performing post over-erase correction repairs threshold voltage of over-erased cells to a higher level with or without adjusting power over-erase correction programming voltage.
4. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 1, further comprising: recording an erase shot number for each erase procedure.
5. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 4, further comprising: comparing the erase shot number with a target cycling-degree to confirm that the erase shot number has reached a target cycling-degree.
6. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 5, wherein the switch condition result is a switch on condition when the erase shot number has reached the target cycling-degree.
7. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 6, wherein the switch on condition turns on the auto-adjusting verification mechanism and the post over-erase correction is performed.
8. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 1, further comprising: detecting a bit line leakage current or recording a repaired bit line amount, and an over-erase correction shot number for each over-erase correction procedure.
9. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 8, further comprising: comparing the bit line leakage current, the repaired bit line amount, and the over-erase correction shot number with a target leakage-degree to confirm that the bit line leakage current, the repaired bit line amount, and the over-erase correction shot number have reached the target leakage-degree.
10. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 9, wherein the switch condition result is a switch on condition when the bit line leakage current, the repaired bit line amount, and the over-erase correction shot number have reached the target leakage-degree.
11. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 10, wherein the switch on condition turns on the auto-adjusting verification mechanism and the post over-erase correction is performed.
12. (canceled)
13. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 1, wherein determining the target degree to obtain a switch condition result considers both erase shot number and g.sub.m degradation.
14. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 1, wherein determining the target degree to obtain a switch condition result considers both repaired bit line amount during over-erase correction and g.sub.m degradation.
15. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 1, wherein determining the target degree to obtain a switch condition result considers both over-erase correction shot number and g.sub.m degradation.
16. A post over-erase correction method comprising: programming a plurality of flash cells; erasing the plurality of flash cells; performing over-erase correction on the plurality of flash cells; performing post over-erase correction on the plurality of flash cells; detecting g.sub.m degradation during the post over-erase correction; and performing post over-erase correction with auto-adjusting verification mechanism based upon detected g.sub.m degradation.
17. The post over-erase correction method according to claim 16, wherein reference current is produced by multiple sets of reference cells or constant current, and performing post over-erase correction with auto-adjusting verification mechanism comprises reducing an amount of reference cells or constant current to lower reference current.
18. The post over-erase correction method according to claim 16, wherein performing post over-erase correction with auto-adjusting verification mechanism repairs threshold voltage of over-erased cells to a higher level with or without adjusting post over-erase correction programming voltage.
19. The post over-erase correction method according to claim 16, further comprising: recording an erase shot number for each erase procedure.
20. The post over-erase correction method according to claim 19, further comprising: comparing the erase shot number with a target cycling-degree to confirm that the erase shot number has reached a target cycling-degree.
21. The post over-erase correction method according to claim 20, further comprising: performing post over-erase correction with auto-adjusting verification mechanism when the erase shot number has reached the target cycling-degree and g.sub.m degradation is detected.
22. The post over-erase correction method according to claim 16, further comprising: detecting a bit line leakage current or recording a repaired bit line amount, and an over-erase correction shot number for each over-erase correction procedure.
23. The post over-erase correction method according to claim 22, further comprising: comparing the bit line leakage current, the repaired bit line amount, and the over-erase correction shot number with a target leakage-degree to confirm that the bit line leakage current, the repaired bit line amount, and the over-erase correction shot number have reached the target leakage-degree.
24. The post over-erase correction method according to claim 23, further comprising: performing post over-erase correction with auto-adjusting verification mechanism when the bit line leakage current, the repaired bit line amount, and the over-erase correction shot number have reached the target leakage-degree and g.sub.m degradation is detected.
25. The post over-erase correction method according to claim 16, further comprising: performing post over-erase correction with auto-adjusting verification mechanism when a repaired bit line amount has reached a target leakage-degree and g.sub.m degradation is detected.
26. The post over-erase correction method according to claim 16, further comprising: performing post over-erase correction with auto-adjusting verification mechanism when an over-erase correction shot number has reached a target leakage-degree and g.sub.m degradation is detected.
27. A post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function comprising: programming a plurality of flash cells; erasing the plurality of flash cells; recording an erase shot number for each erase procedure; performing over-erase correction; comparing the erase shot number with a target cycling-degree; and turning on the auto-adjusting verification mechanism and performing post over-erase correction based upon the comparison of the erase shot number with the target cycling-degree.
28. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 27, wherein the auto-adjusting verification mechanism is turned on and post over-erase correction is performed when the erase shot number reaches the target cycling-degree.
29. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 27, wherein reference current is produced by multiple sets of reference cells or constant current, and performing post over-erase correction with auto-adjusting verification mechanism comprises reducing an amount of reference cells to lower reference current.
30. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 27, wherein turning on the auto-adjusting verification mechanism repairs threshold voltage of over-erased cells to a higher level with or without adjusting post over-erase correction programming voltage.
31. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 27, further comprising: detecting a bit line leakage current or recording a repaired bit line amount, and an over-erase correction shot number for each over-erase correction procedure.
32. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 31, further comprising: comparing the bit line leakage current, the repaired bit line amount, and the over-erase correction shot number with a target leakage-degree to confirm that the bit line leakage current, the repaired bit line amount, and the over-erase correction shot number have reached the target leakage-degree.
33. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 32, wherein the auto-adjusting verification mechanism is turned on and the post over-erase correction is performed when the erase shot number reaches the target cycling-degree and the bit line leakage current, the repaired bit line amount, and the over-erase correction shot number have reached the target leakage-degree.
34. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 27, further comprising: detecting g.sub.m degradation during the post over-erase correction.
35. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 34, wherein the auto-adjusting verification mechanism is turned on and the post over-erase correction is performed when the erase shot number reaches the target cycling-degree and g.sub.m degradation is detected.
36. A post over-erase correction method comprising: detecting g.sub.m degradation of flash cells; detecting leakage-degree of the flash cells; and performing post over-erase correction on the flash cells based on detected g.sub.m degradation or detected leakage-degree.
37. The post over-erase correction method according to claim 36, wherein post over-erase correction is performed when g.sub.m degradation is detected.
38. The post over-erase correction method according to claim 36, wherein post over-erase correction is performed when leakage-degree reaches a target leakage-degree.
39. The post over-erase correction method according to claim 36, wherein post over-erase correction is performed when a bit line leakage current, a repaired bit line amount, or an over-erase correction shot number reaches a target leakage-degree.
40. The post over-erase correction method according to claim 36, the post over-erase correction comprising adjusting an amount of reference cells or constant current to adjust reference current.
41. The post over-erase correction method according to claim 36, wherein reference current is produced by multiple sets of reference cells or constant current and performing post over-erase correction comprises reducing an amount of reference cells or constant current to lower reference current.
42. The post over-erase correction method according to claim 36, wherein performing post over-erase correction repairs threshold voltage of over-erased cells to a higher level with or without adjusting post over-erase correction programming voltage.
43. The post over-erase correction method according to claim 36, further comprising: comparing a bit line leakage current, a repaired bit line amount, and an over-erase correction shot number with a target leakage-degree to confirm that the bit line leakage current, the repaired bit line amount, and the over-erase correction shot number have reached the target leakage-degree.
44. The post over-erase correction method according to claim 36, wherein the post over-erase correction is performed when an erase shot number reaches a target cycling-degree and g.sub.m degradation is detected.
45. The post over-erase correction method with an auto-adjusting verification mechanism and a leakage degree detection function according to claim 36, wherein the post over-erase correction is performed when an erase shot number reaches a target cycling-degree and detected leakage-degree reaches a target leakage-degree.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0030]
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DETAILED DESCRIPTION OF THE INVENTION
[0045] To facilitate understanding of the object, characteristics and effects of this present disclosure, embodiments together with the attached drawings for the detailed description of the present disclosure are provided.
[0046] Refer to
[0047] After cycling, the POEC2 repairs Vt of over-erased cells to a higher level for solving leakage issues. Such solutions are obtaining a reasonable read margin and tpp after cycling while the increased erase time is acceptable since the allowable block erase time is longer after cycling. Moreover, the risk of over soft-programming due to degradation of programmability after cycling is also reduced. The programming voltage of the POEC can be changed to a lower level to further reduce the risk of over soft-programming.
[0048] The POEC verification method 500 begins by pre-programming the flash cells in Step 510. In Step 520 the flash cells are erased and over-erase correction is performed in Step 530.
[0049] In Step 540, determination is made on whether or not to switch on the POEC method with adjustable verification mechanism (POEC2). If it is determined to switch on the POEC method, perform post over-erase correction using the adjustable verification mechanism in Step 560 and then end in Step 590. If it is determined to not switch on the POEC method with adjustable verification, perform post over-erase correction in Step 550 and then end in Step 590.
[0050] There are several methods to determine the switch condition of the POEC mechanism.
[0051] Refer to
[0052] The embodiment of the present invention illustrated in
[0053] In Step 520, the flash cells are erased and over-erase correction is performed in Step 530. For each erase operation the erase shot number is recorded in Step 525. In Step 540, the erase shot number is used to determine whether or not the erase shot number has reached a target cycling-degree.
[0054] If the erase shot number has reached the target cycling-degree, the POEC method with adjustable verification mechanism is switched on and post over-erase correction with the adjustable verification mechanism (Step 560 of
[0055] If the erase shot number has not reached the target cycling-degree, the POEC method with adjustable verification mechanism is not switched on and post over-erase correction (Step 550 of
[0056] Refer to
[0057] The embodiment of the present invention illustrated in
[0058] In Step 520 the flash cells are erased and over-erase correction is performed in Step 530. For each over-erase correction operation, the amount of repaired BLs and the OEC shot number are recorded in Step 533. In Step 540 the amount of repaired BLs and the OEC shot number are used to determine whether or not the amount of repaired BLs and the OEC shot number have reached a target cycling-degree.
[0059] If the amount of repaired BLs, and the OEC shot number have reached a target cycling-degree, the POEC method with adjustable verification mechanism is switched on and post over-erase correction with adjustable verification mechanism (Step 560 of
[0060] If the amount of repaired BLs and the OEC shot number have not reached the target cycling-degree, the POEC method with adjustable verification mechanism is not switched on and post over-erase correction (Step 550 of
[0061] The embodiment of the present invention illustrated in
[0062] The embodiment of the present invention illustrated in
[0063] In Step 520 the flash cells are erased, over-erase correction1 (OEC1) is performed in Step 530. In Step 533 over-erase correction verification2 (OECV2) is performed to checked the BL leakage after OEC1 whether it causes the OFF current. Different verified conditions are used for OEC1 and OECV2. For example, the verification WL voltage of OEC1 is 0V and IREF=Ioecv1=4 uA; the verification WL voltage of OEC2 is 1V and IREF=Ioecv2<14 uA. When OEC1 is performed and verification passed in Step 530, if the result of OECV2 verification is pass in Step 533, i.e. the cell current is less than Ioecv2, which means this bit line will contribute to the OFF current after POEC1 is performed or means gm degradation. It is required to switch on the POEC method with adjustable verification mechanism (POEC2). If the result of OECV2 verification is fail in Step 533, i.e. the cell current is greater than Ioecv2, which means this bit line will not contribute to the OFF current after POEC1 is performed or means gm normal. It is not required to switch on the POEC method with adjustable verification mechanism (POEC2). In Step 540, determination is made on whether or not to switch on the POEC method with adjustable verification mechanism (POEC2). If it is determined to switch on the POEC method, perform post over-erase correction using the adjustable verification mechanism in Step 560 and then end in Step 570. If it is determined to not switch on the POEC method with adjustable verification, perform post over-erase correction in Step 550 and then end in Step 570.
[0064] The embodiment of the present invention illustrated in
[0065] In Step 520 the flash cells are erased, over-erase correction1 (OEC1) is performed in Step 530 and post over-eras correction1 (POEC1) is performed in Step 550. In Step 533 over-erase correction verification2 (OECV2) is performed to detect the BL leakage. In Step 540 check whether or not the BL leakage current is greater than a target leakage. Different verified conditions are used for OEC1 and OECV2. For example, the verification WL voltage of OEC1 is 0V˜0.5V and IREF=Ioecv1=4 uA. The verification WL voltage of OEC2 is 0.3V˜1V and the IREF=Ioecv1=4 uA.
[0066] If the BL leakage current is greater than a target leakage, the POEC method with adjustable verification mechanism is switched on and post over-erase correction with adjustable verification mechanism (Step 560) is performed.
[0067] If the BL leakage current is not greater than a target leakage, the POEC method with adjustable verification mechanism is not switched on and the method is done in Step 570.
[0068] Refer to
[0069] The g.sub.m degradation of flash cells is detected during the first POEC mechanism operation or after the first POEC mechanism (POEC1) is finished. If g.sub.m degradation is detected, the POEC with adjustable verification mechanism (POEC2) is performed to further repair the Vt of flash cells to a higher level with or without adjusting the programming voltage of POEC.
[0070] The adjustable verification mechanism illustrated in
[0071] In Step 520 the flash cells are erased and over-erase correction is performed in Step 530. In Step 545, the post over-erase correction mechanism is performed.
[0072] The POEC mechanism of Step 545 comprises performing the POEC with mechanism 1 (POEC1).
[0073] In Step 555, determine if there is g.sub.m degradation. If g.sub.m degradation is detected, switch on the POEC2 method and perform the POEC method with adjustable verification mechanism in Step 560. After performing the POEC2 method, the method is done in Step 570.
[0074] If g.sub.m degradation is not detected in Step 555, the POEC2 method is not switched on and the method is done in Step 570.
[0075] Refer to
[0076] In the embodiment illustrated in
[0077] Refer to
[0078] Different combinations of the method of the present invention mentioned above are used to determine the switching condition of the POEC.
[0079] For example, the following conditions are used in various embodiments.
[0080] Consider only one of either the erase shot number, the repaired BL amount during OEC, the OEC shot number, the BL leakage current, or g.sub.m degradation.
[0081] Consider both the erase shot number and g.sub.m degradation, as shown in
[0082] Consider both the repaired BL amount during OEC and g.sub.m degradation.
[0083] Consider both the OEC shot number and g.sub.m degradation. Consider both the BL leakage current and g.sub.m degradation.
[0084] In the embodiment illustrated in
[0085] In Step 520 the flash cells are erased and over-erase correction is performed in Step 530. For each erase operation the erase shot number is recorded in Step 525. In Step 540 the erase shot number is used to determine whether or not the erase shot number has reached a target cycling-degree.
[0086] If the erase shot number has not reached a target cycling-degree, POEC1 is performed in Step 550 and the method is done in Step 570.
[0087] If the erase shot number has reached the target cycling-degree, in Step 555, determine if g.sub.m degradation is detected.
[0088] If g.sub.m degradation is detected in Step 555, switch on the POEC2 method and perform the POEC method with adjustable verification mechanism (POEC2) in Step 560.
[0089] If g.sub.m degradation is not detected in Step 555, do not switch on the POEC2 method and post over-erase correct is performed with mechanism 1 (POEC1). After that, the method is done in Step 570.
[0090] Refer to
[0091] As shown in
[0092] Two methods are used to change the verification mechanism of the POEC. Since the reference current is established by reference cells or constant current, the current comparison mechanism can be changed by modulating word line (WL) voltage or the reference current, as shown in
[0093] While the present disclosure has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the present disclosure set forth in the claims.