Apparatus, system, and method for determining a read voltage threshold for solid-state storage media

• US 8,315,092 B2
• Filed: 01/27/2011
• Issued: 11/20/2012
• Est. Priority Date: 01/27/2010
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Fusion-IO Incorporated (Western Digital Corporation)
• Inventors: Strasser, John, Flynn, David, Fillingim, Jeremy, Wood, Robert
• Primary Examiner(s): PHAN, TRONG Q
• Application Number:
  US13/015,458
• Publication Number:
  US 20110182119A1
• Time in Patent Office: 663 Days
• Field of Search: 365/185.03, 365/185.09, 365/185.11, 365/185.12, 365/185.18, 365/185.2, 365/185.24, 365/185.29, 365/185.33
• US Class Current: 365/185.03
• CPC Class Codes: G11C 16/28 using differential sensing or reference cells, e.g. dummy cells
• CPC Class Codes: G11C 29/02 Detection or location of defective auxiliary circuits, e.g. defective refresh counters
• CPC Class Codes: G11C 29/021 in voltage or current generators
• CPC Class Codes: G11C 29/026 in sense amplifiers
• CPC Class Codes: G11C 29/028 with adaption or trimming of parameters
• CPC Class Codes: G11C 29/42 using error correcting codes [ECC] or parity check

Abstract

An apparatus, system, and method are disclosed for determining a read voltage threshold for solid-state storage media. A data set read module reads a data set from storage cells of solid-state storage media. The data set is originally stored in the storage cells with a known bias. A deviation module determines that a read bias for the data set deviates from the known bias. A direction module determines a direction of deviation for the data set. The direction of deviation is based on a difference between the read bias of the data set and the known bias. An adjustment module adjusts a read voltage threshold for the storage cells of the solid-state storage media based on the direction of deviation.

Claims

1. A method to determine a direction to adjust a read voltage threshold for solid-state storage media, the method comprising:

reading a data set from storage cells of solid-state storage media, the data set originally stored in the storage cells with a known bias;

determining that a read bias for the data set deviates from the known bias; and

determining a direction of deviation for the data set based on a difference between the read bias and the known bias.

2. The method of Claim 1, further comprising adjusting a read voltage threshold for the storage cells of the solid-state storage media based on the direction of deviation.

3. The method of Claim 2, wherein the read voltage threshold is adjusted in the direction of deviation.

4. The method of Claim 2, wherein adjusting the read voltage threshold for the storage cells of the solid-state storage media is based at least partially on one or more statistics for a solid-state storage device of the solid-state storage media.

5. The method of Claim 4, wherein at least one of the one or more statistics is selected from the group consisting of a temperature for the solid-state storage device, an error rate for the solid-state storage device, an erase cycle count for the solid-state storage device, and a storage request latency for the solid-state storage device.

6. The method of Claim 1, wherein the known bias comprises an expected bias for data stored by the solid-state storage media based on a reversible biasing algorithm applied to data written to the solid-state storage media.

7. The method of Claim 1, wherein the known bias comprises an error corrected state of bits of the data set and the read bias comprises an error bias indicating one or more bits of the data set that are in error.

8. The method of Claim 7, further comprising receiving the known bias and the error bias for the data set from an error correction code (“

ECC”

) decoder, the ECC decoder changing the one or more bits that are in error to the error corrected state.

9. The method of Claim 1, wherein determining that the read bias for the data set deviates from the known bias and determining the direction of deviation are performed in response to detecting an uncorrectable data error in the data set.

10. The method of Claim 1, wherein the known bias comprises a known ratio of binary ones and binary zeroes.

11. The method of Claim 10, wherein the known ratio is greater than zero and less than one such that the direction of deviation in either direction of the known ratio is detectable.

12. The method of Claim 10, wherein the known ratio is offset between a ratio of exclusively binary ones and a ratio of exclusively binary zeroes such that the direction of deviation may occur in either direction from the known ratio.

13. The method of Claim 1, wherein the data set comprises a sample data set read in response to a testing operation.

14. The method of Claim 1, wherein the data set comprises a requested data set read in response to a read request from a client.

15. The method of Claim 14, wherein the data set comprises the requested data set and further comprises an amount of additional data read from the solid-state storage media with the requested data set, the amount of additional data sized to fit within excess read bandwidth of the solid-state storage media such that reading the amount of additional data does not affect a read bandwidth for retrieving the requested data set from the solid-state storage media.

16. The method of Claim 1, further comprising determining that the data set was read from a specific grouping of storage cells based on a position of the data set within a sequence of data sets, the solid-state storage media comprising a plurality of groupings of storage cells, data from each grouping of storage cells read during a read operation.

17. The method of Claim 16, wherein each grouping of storage cells comprises a solid-state storage media die.

18. The method of Claim 16, wherein data from each grouping of storage cells is read in parallel during the read operation.

19. The method of Claim 1, wherein the storage cells comprise multi-level storage cells and the data set comprises a subset of binary data that the multi-level storage cells store.

20. The method of Claim 19, wherein the subset of binary data is read from a lower page of the multi-level storage cells, each multi-level storage cell having a plurality of states encoded according to an encoding model such that each state represents two or more bits of the multi-level storage cell having one of two different binary values.

21. The method of Claim 20, wherein determining a direction of deviation for the data set comprises determining that the direction of deviation is toward a larger read voltage in response to the difference between the read bias and the known bias indicating that one or more storage cell values have transitioned from a binary one to a binary zero.

22. The method of Claim 20, wherein determining a direction of deviation for the data set comprises determining that the direction of deviation is toward a smaller read voltage in response to the difference between the read bias and the known bias indicating that one or more storage cell values have transitioned from a binary zero to a binary one.

23. An apparatus for determining a read voltage threshold for solid-state storage media, the apparatus comprising:

a data set read module that reads a data set from storage cells of solid-state storage media, the data set originally stored in the storage cells with a known bias;

a deviation module that determines that a read bias for the data set deviates from the known bias;

a direction module that determines a direction of deviation for the data set, the direction of deviation comprising a difference between the read bias and the known bias; and

an adjustment module that adjusts a read voltage threshold for the storage cells of the solid-state storage media based on the direction of deviation.

24. The apparatus of Claim 23, further comprising an ECC decoder that provides the known bias and the read bias to the deviation module, wherein the known bias comprises an error corrected state of bits of the data set and the read bias comprises an error bias indicating one or more bits of the data set that are in error.

25. The apparatus of Claim 23, further comprising an inverse bias module that provides the known bias and the read bias to the deviation module, wherein the known bias comprises an expected bias for data stored by the solid-state storage media based on a reversible biasing algorithm applied to data written to the solid-state storage media.

26. The apparatus of Claim 23, further comprising a device factor module that provides, to the adjustment module, one or more statistics for a solid-state storage device of the solid-state storage media, wherein the adjustment module adjusts the read voltage threshold for the storage cells of the solid-state storage media at least partially based on the one or more statistics for the solid-state storage device.

27. A system for determining a direction to adjust a read voltage threshold for solid-state storage media, the system comprising:

a solid-state storage device comprising solid-state storage media;

a storage controller for the solid-state storage device, the storage controller comprising,

a data set read module that reads a data set from storage cells of the solid-state storage media, the data set originally stored in the storage cells with a known bias;

a deviation module that determines that a read bias for the data set deviates from the known bias;

a direction module that determines a direction of deviation for the data set, the direction of deviation comprising a difference between the read bias and the known bias; and

an adjustment module that adjusts a read voltage threshold for the storage cells of the solid-state storage media based on the direction of deviation.

28. The system of Claim 27, wherein the deviation module uses an error bias as the known bias in response to the one or more correctable errors in the data set and the deviation module uses an expected bias as the known bias in response to one or more uncorrectable errors in the data set, the error bias indicating one or more bits of the data set that are in error and the expected bias based on a reversible biasing algorithm applied to data written to the solid-state storage media.