Adaptive erase and soft programming for memory
View Patent ↗An erase sequence of a non-volatile storage device includes an erase operation followed by a soft programming operation. The erase operation applies one or more erase pulses to the storage elements, e.g., via a substrate, until an erase verify level is satisfied. The number of erase pulses is tracked and recorded as an indicia of the number of programming-erase cycles which the storage device has experienced. The soft programming operation applies soft programming pulses to the storage elements until a soft programming verify level is satisfied. Based on the number of erase pulses, the soft programming operation time is shortened by skipping verify operations for a specific number of initial soft programming pulses which is a function of the number of erase pulses. Also, a characteristic of the soft programming operation can be optimized, such as starting amplitude, step size or pulse duration.
1. A method for operating non-volatile storage, comprising:
applying one or more erase pulses to a set of non-volatile storage elements until a first verify condition is satisfied;
determining a count of the erase pulses applied; and
applying a number N SPGM-SKIP of one or more soft programming pulses to the set of non-volatile storage elements without performing verify operations, N SPGM-SKIP is based on the count, and subsequently applying one or more additional soft programming pulses to the set of non-volatile storage elements until a second verify condition is satisfied, each soft programming pulse of the one or more additional soft programming pulses is followed by a verify operation.
2. The method of claim 1 , further comprising:
categorizing the set of non-volatile storage elements into one group of multiple available groups based on the count, where N SPGM-SKIP is based on the group into which the set of non-volatile storage elements is categorized.
3. The method of claim 1 , further comprising:
responsive to the second verify condition being satisfied, programming at least one of the non-volatile storage elements in the set to a higher data state.
4. The method of claim 1 , wherein:
N SPGM-SKIP is based on a count of erase pulses applied in multiple erase operations.
5. The method of claim 1 , wherein:
the set of non-volatile storage elements has a first threshold voltage distribution which is below an erased state, at least in part, when the first verify condition is satisfied, and a second, tighter threshold voltage distribution at the erased state when the second verify condition is satisfied.
6. The method of claim 1 , wherein:
the applying one or more erase pulses is part of an erase operation of a first erase sequence, and the applying the number N SPGM-SKIP of one or more soft programming pulses is part of a soft programming operation of the first erase sequence.
7. The method of claim 6 , further comprising:
performing an additional erase operation of a second erase sequence in which a number of erase verify pulses is skipped based on the count.
8. A method for operating non-volatile storage, comprising:
performing an erase operation of an erase sequence, including applying one or more erase pulses to a set of non-volatile storage elements until an erase verify condition is satisfied;
determining a count of the erase pulses applied; and
performing a soft programming operation of the erase sequence, including applying one or more soft programming pulses to the set of non-volatile storage elements until a soft programming verify condition is satisfied, a characteristic of the one or more soft programming pulses is set based on the count.
9. The method of claim 8 , wherein:
the characteristic comprises a level of a first soft programming pulse of the one or more soft programming pulses.
10. The method of claim 8 , wherein:
the characteristic comprises a step size of the one or more soft programming pulses.
11. The method of claim 8 , wherein:
the characteristic comprises a maximum limit on a number of the one or more soft programming pulses.
12. The method of claim 8 , wherein:
the characteristic comprises a limit of an energy of the one or more soft programming pulses.
13. The method of claim 8 , wherein:
the characteristic comprises a pulse width of the one or more soft programming pulses.
14. The method of claim 8 , further comprising:
performing a programming operation which involves a transition between data states for at least one of the non-volatile storage elements, responsive to completion of the soft programming operation.
15. The method of claim 8 , wherein:
the applying one or more soft programming pulses comprises applying a number N N SPGM-SKIP SKIP of one or more soft programming pulses without performing verify operations, the number N SPGM-SKIP is based on the count, and subsequently applying one or more additional soft programming pulses, each soft programming pulse of the one or more additional soft programming pulses is followed by a verify operation.
16. A non-volatile storage apparatus, comprising:
a set of non-volatile storage elements; and
at least one control circuit, the at least one control circuit applies one or more erase pulses to the set of non-volatile storage elements until a first verify condition is satisfied, determines a count of the erase pulses applied, and applies a number Nspgm-skip of one or more soft programming pulses to the set of non-volatile storage elements without performing verify operations, Nspgm-skip is based on the count, and subsequently applies one or more additional soft programming pulses to the set of non-volatile storage elements until a second verify condition is satisfied, each soft programming pulse of the one or more additional soft programming pulses is followed by a verify operation.
17. The non-volatile storage apparatus of claim 16 , wherein:
the at least one control circuit categorizes the set of non-volatile storage elements into one group of multiple available groups based on the count, where Nspgm-skip is based on the group into which the set of non-volatile storage elements is categorized.
18. The non-volatile storage apparatus of claim 16 , wherein:
the applying one or more erase pulses is part of an erase operation of a first erase sequence, and the applying the number Nspgm-skip of one or more soft programming pulses is part of a soft programming operation of the first erase sequence.
19. The non-volatile storage apparatus of claim 16 , wherein:
at least one of a level, step size and pulse width of at least one of the one or more soft programming pulses is set based on the count.
20. The non-volatile storage apparatus of claim 16 , wherein:
the one or more erase pulses are applied as part of an erase operation of a first erase sequence, and the number Nspgm-skip of one or more soft programming pulses are applied as part of a soft programming operation of the first erase sequence; and
the at least one control circuit performs an additional erase operation of a second erase sequence in which a number of erase verify pulses is skipped based on the count.