Providing reliability metrics for decoding data in non-volatile storage

• US 8,966,350 B2
• Filed: 05/06/2013
• Issued: 02/24/2015
• Est. Priority Date: 03/29/2007
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Sandisk Technologies Incorporated (Western Digital Corporation)
• Inventors: Mokhlesi, Nima, Chin, Henry, Zhao, Dengtao
• Primary Examiner(s): Torres, Joseph D
• Application Number:
  US13/888,145
• Publication Number:
  US 20130246720A1
• Time in Patent Office: 659 Days
• Field of Search: 714/780, 714/794, 714/795
• US Class Current: 714/780
• CPC Class Codes: G06F 12/00 Accessing, addressing or allocating within memory systems or architectures digital input from, or digital output to record carriers, e.g. to disk storage units, G06F3/06
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/04 using variable threshold transistors, e.g. FAMOS
• CPC Class Codes: G11C 16/28 using differential sensing or reference cells, e.g. dummy cells
• CPC Class Codes: G11C 29/00 Checking stores for correct operation ; Subsequent repair; Testing stores during standby or offline operation
• CPC Class Codes: G11C 29/02 Detection or location of defective auxiliary circuits, e.g. defective refresh counters
• CPC Class Codes: G11C 29/028 with adaption or trimming of parameters
• CPC Class Codes: H03M 13/11 using multiple parity bits
• CPC Class Codes: H03M 13/37 Decoding methods or techniques, not specific to the particular type of coding provided for in groups H03M13/03 - H03M13/35

Abstract

A set of reliability metrics is provided for use by an iterative probabilistic decoding process for non-volatile storage. A plurality of sense operations are performed on at least one set of non-volatile storage elements which are programmed to a plurality of programming states. A set of reliability metrics such as logarithmic likelihood ratios is provided based on the sense operations. The set of reliability metrics is can be used by an iterative probabilistic decoding process in determining a programming state of at least one non-volatile storage element based on at least one subsequent sense operation involving the at least one non-volatile storage element. The plurality of sense operations can be performed at different ages (e.g., number of program/erase cycles) of the at least one set of non-volatile storage elements and the set of reliability metrics can be based on an average over the different ages.

Claims

1. A method for operating non-volatile storage, comprising:

performing a plurality of sense operations on at least one set of non-volatile storage elements which are programmed to a plurality of programming states, wherein the plurality of sense operations comprise sense operations which are performed when the set of non-volatile storage elements has a first number of program/erase cycles and sense operations which are performed when the set of non-volatile storage elements has a second number of program/erase cycles;

providing a set of reliability metrics based on the plurality of sense operations; and

storing the set of reliability metrics for an iterative probabilistic decoding process in determining a programming state of at least one non-volatile storage element based on at least one subsequent sense operation involving the at least one non-volatile storage element, wherein the non-volatile storage element is in the set of non-volatile storage elements.

2. The method of claim 1, further comprising:

obtaining measurements of threshold voltage distributions for the set of non-volatile storage elements based on the sense operations which are performed when the set of non-volatile storage elements has the first number of program/erase cycles;

obtaining measurements of threshold voltage distributions for the set of non-volatile storage elements based on the sense operations which are performed when the set of non-volatile storage elements has the second number of program/erase cycles;

averaging the measurements of threshold voltage distributions for the set of non-volatile storage elements based on the sense operations which are performed when the set of non-volatile storage elements has the first number of program/erase cycles with the measurements of threshold voltage distributions for the set of non-volatile storage elements based on the sense operations which are performed when the set of non-volatile storage elements has the second number of program/erase cycles to obtained averaged measurements of threshold voltage distributions; and

providing the set of reliability metrics based on the averaged measurements of threshold voltage distributions.

3. The method of claim 1, wherein:

the set of reliability metrics is based on conditional probability functions which are based on the plurality of sense operations.

4. The method of claim 1, wherein:

the set of reliability metrics comprise logarithmic likelihood ratios which are based on the plurality of sense operations.

5. The method of claim 1, wherein the providing the set of reliability metrics comprises:

determining a conditional probability function f1(u|X) based on the plurality of sense operations, where u indicates a sensed threshold voltage and X represents a programmed state of the plurality of programming states; and

determining a probability function f2(v) based on the plurality of sense operations, for each programming state, where v indicates a deviation of a sensed threshold voltage from a threshold voltage free of read noise.

6. The method of claim 5, wherein the providing the set of reliability metrics further comprises:

determining logarithmic likelihood ratios based on the conditional probability function f1(u|X) and the probability function f2(v).