Multi-tier detection and decoding in flash memories

• US 9,898,361 B2
• Filed: 12/31/2012
• Issued: 02/20/2018
• Est. Priority Date: 01/04/2011
• Status: Active Grant

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Inventors: Haratsch, Erich F., Alhussien, Abdel Hakim S.
• Primary Examiner(s): Shah, Sanjiv
• Assistant Examiner(s): Gossage, Glenn
• Application Number:
  US13/731,551
• Publication Number:
  US 20130185598A1
• Time in Patent Office: 1,877 Days
• CPC Class Codes: G06F 11/10 Adding special bits or symbols to the coded information, e.g. parity check, casting out 9's or 11's
• CPC Class Codes: G06F 11/1048 using arrangements adapted for a specific error detection or correction feature
• CPC Class Codes: G06F 11/1072 in multilevel memories
• CPC Class Codes: G11C 11/56 using storage elements with more than two stable states represented by steps, e.g. of voltage, current, phase, frequency
• CPC Class Codes: G11C 16/34 Determination of programming status, e.g. threshold voltage, overprogramming or underprogramming, retention

Abstract

Methods and apparatus are provided for multi-tier detection and decoding in flash memory devices. Data from a flash memory device is processed by obtaining one or more read values for at least one bit in a given page of the flash memory device; converting the one or more read values for the at least one bit to a reliability value; performing an initial decoding of the at least one bit in a given page using the reliability value; and performing an additional decoding of the at least one bit in the given page if the initial decoding is not successful, wherein the additional decoding uses one or more of additional information for the given page and at least one value for at least one bit from at least one additional page.

Claims

1. A method for processing data from a flash memory device, comprising the steps of:

obtaining one or more initial read values for a given page of said flash memory device;

converting, in a first converting step, said one or more initial read values for said given page to a reliability value;

performing an initial decoding of said given page using said reliability value; and

if said initial decoding is not successful, performing the following steps;

obtaining one or more recovery read values using at least one additional read access of said flash memory device for one or more of said given page and at least one additional page of said flash memory device, wherein said given page and said at least one additional page comprise a plurality of bits, wherein said at least one additional page is in one or more of a same wordline and a different wordline as said given page, wherein said at least one additional read access comprises one or more of (i) reading substantially all of said at least one additional page in the same wordline as said given page;

(ii) reading substantially all of the same wordline as said given page a plurality of times; and

(iii) reading substantially all of one or more wordlines neighboring the same wordline as said given page;

converting, in a second converting step, said one or more initial read values and said one or more recovery read values to at least one regenerated reliability value; and

performing an additional decoding of said given page using said at least one regenerated reliability value.

2. The method of claim 1, wherein said additional decoding uses additional information for said given page comprising soft values based on a quantized estimate of a voltage stored on a cell of said flash memory device storing said given page.

3. The method of claim 2, wherein said quantized estimate of said voltage comprises one or more of hard decisions obtained by a plurality of read retries of said cell at a plurality of reference voltages and soft values directly from said flash memory device.

4. The method of claim 1, wherein said one or more recovery read values comprises one or more soft values from said at least one additional page in the same wordline as said given page.

5. The method of claim 1, wherein said at least one additional page is in a different wordline than said given page, and wherein said one or more recovery read values is obtained for said at least one additional page and used to generate said at least one regenerated reliability value for said given page.

6. The method of claim 5, wherein said one or more recovery read values is used to generate said at least one regenerated reliability value for said given page based on intercell interference mitigation.

7. The method of claim 1, wherein said one or more initial read values and said one or more recovery read values comprise one or more of a hard value and a soft value.

8. The method of claim 1, wherein said flash memory device comprises a plurality of cells each capable of storing at least two levels per cell.

9. The method of claim 1, wherein one or more of said initial decoding and said additional decoding comprises a Low Density Parity Check Message Passing decoding.

10. The method of claim 1, wherein said initial decoding is performed in real-time and said additional decoding is performed in an offline manner.

11. The method of claim 1, wherein one or more of said initial decoding and said additional decoding is iteratively performed a plurality of times.

12. The method of claim 1, further comprising one or more of providing an output of said initial decoding in a feedback manner to said first converting step in a local iteration mode, and providing an output of said additional decoding in a feedback manner to said second converting step in a global iteration mode.

13. The method of claim 1, wherein said reliability value comprises one or more of a log-likelihood ratio and an approximation of a log-likelihood ratio.

14. The method of claim 1, wherein said additional decoding comprises a multi-tier process comprising a plurality of error recovery steps employing said at least one additional read access.

15. The method of claim 1, wherein said following steps comprise a multi-tier process comprising a plurality of error recovery steps, wherein an order of said plurality of error recovery steps is programmable.

16. The method of claim 1, wherein said following steps comprise a multi-tier process comprising a plurality of error recovery stages, wherein said plurality of error recovery stages comprises successive stages of one or more of increasing latency and increasing error correction capabilities.

17. The method of claim 1, wherein said following steps comprise a multi-tier process comprising a plurality of detection and decoding modes, wherein said plurality of detection and decoding modes have progressively increasing complexity.

18. The method of claim 17, further comprising the step of converting one or more read values for each of said plurality of detection and decoding modes to one or more of said at least one regenerated reliability value.

19. A tangible machine-readable recordable storage medium for processing data from a flash memory device, wherein one or more software programs stored on said tangible machine-readable recordable storage medium when executed by one or more processing devices implement the steps of the method of claim 1.

20. A method for processing data from a flash memory device, comprising:

obtaining one or more read values for a given page of said flash memory device;

converting said one or more read values for said given page to a reliability value;

performing an initial decoding of said given page using said reliability value; and

if said initial decoding is not successful, performing the following steps;

obtaining one or more recovery read values using at least one additional read access of said flash memory device for one or more of said given page and at least one additional page of said flash memory device, wherein said given page and said at least one additional page comprise a plurality of bits, wherein said at least one additional page is in one or more of a same wordline and a different wordline as said given page, wherein said at least one additional read access comprises one or more of (i) reading substantially all of said at least one additional page in the same wordline as said given page;

(ii) reading substantially all of the same wordline as said given page a plurality of times; and

(iii) reading substantially all of one or more wordlines neighboring the same wordline as said given page; and

performing an additional decoding of said given page, wherein said additional decoding comprises one or more of the following steps;

regenerating said reliability value for said given page in a first regenerating step using at least one of said one or more recovery read values for said at least one additional page and decoding said given page using said regenerated reliability value, wherein said at least one additional page is in a same wordline as said given page;

obtaining a quantized estimate of a voltage stored on a cell of said flash memory device storing said given page and decoding said given page based on said quantized estimate, wherein said quantized estimate of said voltage is used as said at least one of said one or more recovery read values; and

regenerating said reliability value for said given page in a second regenerating step using at least one of said one or more recovery read values for said at least one additional page and decoding given page using said reliability value generated in the second regenerating step, wherein said at least one additional page is in a different wordline than said given page.

21. The method of claim 20, wherein said second regenerating step performs intercell interference estimation and mitigation when regenerating said reliability value.

22. The method of claim 20, wherein said quantized estimate of said voltage comprises one or more of hard decisions obtained by a plurality of read retries of said cell at a plurality of reference voltages and soft values directly from said flash memory device.

23. The method of claim 20, wherein said additional decoding comprises said first regenerating step if said initial decoding is not successful, followed by said step of obtaining a quantized estimate if said first regenerating step is not successful, followed by said second regenerating step if said step of obtaining a quantized estimate is not successful.

24. A flash memory system, comprising:

a reliability unit for converting (i) one or more initial read values for a given page to a reliability value, and (ii) said one or more initial read values and one or more recovery read values obtained using at least one additional read access of said flash memory device for one or more of said given page and at least one additional page of said flash memory device to at least one regenerated reliability value, wherein said at least one additional read access comprises one or more of (i) reading substantially all of said at least one additional page in the same wordline as said given page;

(ii) reading substantially all of the same wordline as said given page a plurality of times; and

(iii) reading substantially all of one or more wordlines neighboring the same wordline as said given page, and wherein said one or more recovery read values are obtained if an initial decoding of said given page is not successful; and

a decoder for performing (i) said initial decoding of said given page using said reliability value; and

(ii) an additional decoding of said given page using said at least one regenerated reliability value if said initial decoding is not successful.

25. The flash memory system of claim 24, wherein said additional decoding uses additional information for said given page comprising soft values based on a quantized estimate of a voltage stored on a cell of said flash memory device storing said given page.

26. The flash memory system of claim 24, wherein said one or more recovery read values comprises one or more soft values from said at least one additional page of the same wordline as said given page.

27. The flash memory system of claim 24, wherein said at least one additional page is in a different wordline than said given page, and wherein said one or more recovery read values is obtained for said at least one additional page and used to generate said at least one regenerated reliability value for said given page.

28. The flash memory system of claim 24, wherein said initial decoding is performed in real-time and said additional decoding is performed in an offline manner.

29. The flash memory system of claim 24, wherein one or more of said initial decoding and said additional decoding is iteratively performed a plurality of times.

30. The flash memory system of claim 24, wherein said additional decoding comprises a multi-tier process comprising a plurality of error recovery steps employing one or more of additional information for said given page and at least one value for said at least one additional page.