Method for programming non-volatile memory with self-adjusting maximum program loop
View Patent ↗The maximum allowable number of voltage programming pulses to program memory elements of a non-volatile memory device is adjusted to account for changes in the memory elements which occur over time. Programming pulses are applied until the threshold voltage of one or more memory elements reaches a certain verify level, after which a defined maximum number of additional pulses may be applied to other memory elements to allow them to also reach associated target threshold voltage levels. The technique enforces a maximum allowable number of programming pulses that can change over time as the memory is cycled.
1. A method for programming non-volatile storage, comprising:
programming at least a first non-volatile storage element to reach a first verify level using a series of voltage pulses;
detecting when the at least a first non-volatile storage element has reached the first verify level; and
enforcing, responsive to the detecting, a maximum allowable number of additional voltage pulses to be used in programming at least a second non-volatile storage element to reach a second verify level.
2. The method of claim 1 , wherein:
the maximum allowable number of additional voltage pulses is enforced based on a sum of: (a) a number of the voltage pulses needed for the at least a first non-volatile storage element to reach the first verify level, and (b) the maximum allowable number of additional voltage pulses.
3. The method of claim 1 , wherein:
the maximum allowable number of additional voltage pulses is variable according to a number of the voltage pulses needed for the at least a first non-volatile storage element to reach the verify level.
4. The method of claim 1 , wherein:
the maximum allowable number of additional voltage pulses is fixed.
5. The method of claim 1 , wherein:
the maximum allowable number of additional voltage pulses is variable.
6. The method of claim 1 , further comprising:
tracking a usage of the at least a first non-volatile storage element over time;
wherein the maximum allowable number of additional voltage pulses is variable according to the usage.
7. The method of claim 6 , wherein:
the tracking of the usage comprises maintaining a count of programming cycles.
8. The method of claim 1 , wherein the at least a first non-volatile storage element comprises a plurality of non-volatile storage elements that are programmed to reach the first verify level using the series of voltage pulses, the method further comprising:
determining a number of the voltage pulses needed for each of the plurality of non-volatile storage elements to reach the first verify level; and
enforcing the maximum allowable number of additional voltage pulses to be used in programming the at least a second non-volatile storage element to reach the second verify level based on the number of the voltage pulses needed for each of the plurality of non-volatile storage elements to reach the first verify level.
9. The method of claim 8 , wherein:
the maximum allowable number of additional voltage pulses for use in programming the at least a second non-volatile storage element to reach the second verify level is enforced based on a statistical metric derived from the number of the voltage pulses needed for each of the plurality of non-volatile storage elements to reach the first verify level.
10. The method of claim 1 , wherein:
the at least a first non-volatile storage element and the at least a second non-volatile storage element are programmed in a common programming cycle.
11. The method of claim 1 , wherein:
the at least a second non-volatile storage element is programmed in a programming cycle which is after a programming cycle in which the at least a first non-volatile storage element is programmed.
12. The method of claim 1 , wherein:
the maximum allowable number of additional voltage pulses is based on a threshold voltage distribution of at least the first non-volatile storage element divided by a step size of the voltage pulses.
13. The method of claim 1 , wherein:
the at least a first non-volatile storage element and the at least a second non-volatile storage element are provided in at least one of a common block and a common segment.
14. The method of claim 1 , wherein:
the at least a first non-volatile storage element and the at least a second non-volatile storage element are programmed with data from a common page.
15. The method of claim 1 , wherein:
at least one of the first and second verify levels is an intermediate voltage level which is before a final voltage level.
16. The method of claim 1 , wherein:
at least one of the first and second verify levels is a final voltage level.
17. A method for programming non-volatile storage, comprising:
performing one or more initial program cycles for a set of non-volatile storage elements until a first subset of said non-volatile storage elements has reached a first verify level; and
performing one or more additional program cycles for said set of non-volatile storage elements subsequent to said first subset of said non-volatile storage elements reaching said first verify level, said one or more additional program cycles not to exceed a predefined maximum number of additional program cycles.
18. The method of claim 17 , wherein:
the maximum number of additional voltage pulses is variable.
19. The method of claim 17 , wherein:
the at least a first non-volatile storage element and the at least a second non-volatile storage element are programmed in a common programming cycle.
20. The method of claim 17 , wherein:
the at least a second non-volatile storage element is programmed in a programming cycle which is after a programming cycle in which the at least a first non-volatile storage element is programmed.
21. A method for programming non-volatile storage, comprising:
detecting when at least a first non-volatile storage element in a set of non-volatile storage elements has reached a first verify level after voltage pulses have been applied thereto; and
enforcing, responsive to the detecting, a maximum allowable number of voltage pulses to be applied to at least a second non-volatile storage element in the set of non-volatile storage elements to cause the at least a second non-volatile storage element to reach a second verify level.
22. The method of claim 21 , wherein:
the maximum allowable number of additional voltage pulses is fixed.
23. The method of claim 21 , wherein:
the maximum allowable number of additional voltage pulses is variable.
24. The method of claim 21 , further comprising:
tracking a usage of the at least a first non-volatile storage element over time;
wherein the maximum allowable number of additional voltage pulses is variable according to the usage.
25. The method of claim 21 , wherein:
the at least a first non-volatile storage element and the at least a second non-volatile storage element are programmed in a common programming cycle.
26. The method of claim 21 , wherein:
the at least a second non-volatile storage element is programmed in a programming cycle which is after a programming cycle in which the at least a first non-volatile storage element is programmed.