Method and system for optimizing reliability and performance of programming data in non-volatile memory devices

• US 20050024978A1
• Filed: 07/26/2004
• Published: 02/03/2005
• Est. Priority Date: 07/30/2003
• Status: Active Grant

• Current Assignee: Western Digital Israel Limited (Western Digital Corporation)
• Original Assignee: M-Systems Flash Disk Pioneers Ltd. (Western Digital Corporation)
• Inventors: Ronen, Amir
• Granted Patent: US 7,437,498 B2
• Time in Patent Office: Days
• US Class Current: 365/232
• CPC Class Codes: G11C 11/5621 using charge storage in a floating gate
• CPC Class Codes: G11C 16/349 Arrangements for evaluating degradation, retention or wearout, e.g. by counting erase cycles

Abstract

Methods of managing memory devices, and devices so managed. A value of a parameter, that is used to program one or more memory cells, is adapted to a monitored condition of the cell(s). Either the number of bits per cell is held fixed or the monitored condition is an intrinsic condition of the cell(s). The initial value of the parameter is optimized for those specific cells, relative to a pre-selected criterion, by programming the cell(s) in accordance with candidate values of the parameter.

Claims

1. A method of managing a memory, comprising the steps of:

(a) programming at least one cell of the memory to store a pre-selected number of bits in accordance with a first respective value of each of at least one parameter;

(b) monitoring a condition of said at least one cell that is associated with said programming in accordance with said at least one first value; and

(c) substituting a second value for at least one of said at least one first value in accordance with said monitoring while keeping said number of bits fixed.

2. The method of claim 1, wherein said at least one cell is grouped into at least one page, and wherein said programming, monitoring and substituting is effected on a per-page basis.

3. The method of claim 2, wherein said at least one page is grouped into at least one block, and wherein said programming, monitoring and substituting are effected on a per-block basis.

4. The method of claim 1, further comprising the step of:

(d) programming said at least one cell in accordance with said at least one second value.

5. The method of claim 1, wherein said at least one parameter is selected from the group consisting of a programming base voltage, a programming iteration stepping voltage, a maximum programming voltage, a maximum number of iterations per programming operation, a programming base pulse duration and a programming iteration stepping duration.

6. The method of claim 1, wherein said condition is related to a programming history of said at least one cell.

7. The method of claim 6, wherein said condition is selected from the group consisting of a number of times that said at least one cell has been programmed, a time of a first said programming of said at least one cell in accordance with said at least one first value, a time of a most recent said programming of said at least one cell in accordance with said at least one first value, a number of errors in programming said at least one cell, a cumulative number of programming iterations of said at least one cell, a number of programming iterations in a most recent programming of said at least one cell and a time since a number of iterations in excess of a predetermined threshold first was needed to program one of said at least one cell.

8. The method of claim 1, wherein said condition is related to an erasure history of said at least one cell.

9. The method of claim 8, wherein said condition is selected from the group consisting of a number of times that said at least one cell has been erased and a time of a most recent erasure of said at least one cell.

10. A method of managing a memory, comprising the steps of:

(a) programming at least one cell of the memory in accordance with a first respective value of each of at least one parameter;

(b) monitoring an intrinsic condition of said at least one cell that is associated with said programming in accordance with said at least one first value; and

(c) substituting a second value for at least one of said at least one first value in accordance with said monitoring.

11. The method of claim 10, wherein said at least one cell is grouped into at least one page, and wherein said programming, monitoring and substituting is effected on a per-page basis.

12. The method of claim 11, wherein said at least one page is grouped into at least one block, and wherein said programming, monitoring and substituting are effected on a per-block basis.

13. The method of claim 10, further comprising the step of:

(d) programming said at least one cell in accordance with said at least one second value.

14. The method of claim 10, wherein said at least one parameter is selected from the group consisting of a programming base voltage, a programming iteration stepping voltage, a maximum programming voltage, a maximum number of iterations per programming operation, a programming base pulse duration and a programming iteration stepping duration.

15. The method of claim 10, wherein said condition is related to a programming history of said at least one cell.

16. The method of claim 15, wherein said condition is selected from the group consisting of a number of errors in programming said at least one cell, a cumulative number of programming iterations of said at least one cell, a number of programming iterations in a most recent programming of said at least one cell and a time since a number of iterations in excess of a predetermined threshold first was needed to program one of said at least one cell.

17. A data storage device, comprising:

(a) a plurality of cells for storing the data;

(b) a programming unit for programming the data into said plurality of cells in accordance with at least one parameter, such that each said cell stores a pre-selected number of bits of the data; and

(c) a mechanism for;

(i) monitoring a condition of said plurality of cells that is associated with said programming in accordance with a first respective value of each said at least one parameter, and

(ii) substituting a second value for at least one of said at least one first value in accordance with said monitoring while keeping said number of bits fixed.

18. A data storage device, comprising:

(a) a plurality of cells for storing the data;

(b) a programming unit for programming the data into said plurality of cells in accordance with at least one parameter; and

(c) a mechanism for;

(i) monitoring an intrinsic condition of said plurality of cells that is associated with said programming in accordance with a first respective value of each said at least one parameter, and

(ii) substituting a second value for at least one of said at least one first value in accordance with said monitoring.

19. A method of managing a memory, comprising the steps of:

for at least one cell of the memory;

(a) selecting a criterion for optimizing at least one programming parameter of the at least one cell; and

(b) optimizing said at least one programming parameter relative to said criterion, thereby obtaining an optimum value of each said at least one programming parameter that is specific to the at least one cell.

20. The method of claim 19, wherein said optimizing includes programming said at least one cell.

21. The method of claim 19, wherein said criterion is that a number of programming iterations needed to program said at least one cell is minimized.

22. The method of claim 19, wherein said at least one programming parameter includes a programming base voltage.

23. The method of claim 19, wherein said at least one programming parameter includes a programming iteration stepping voltage.

24. The method of claim 19, wherein at least two said programming parameters are optimized jointly.

25. A data storage device, comprising:

(a) a plurality of cells for storing the data;

(b) a programming unit for programming the data into said plurality of cells in accordance with at least one parameter; and

(c) a mechanism for optimizing said at least one parameter, for at least a portion of said plurality of cells, relative to a pre-selected criterion, thereby obtaining an optimum value, of each said at least one parameter, that is specific to said at least portion of said plurality of cells.

26. The data storage device of claim 25, wherein said optimizing includes programming said plurality of cells using said programming unit.