Nonvolatile Memory Error Correction Using Weak Column Weighting
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Solution Overview
Problem
The increasing integration density and number of bits in nonvolatile memory devices lead to decreased data reliability, particularly due to defective or degraded cell strings and weak columns with back pattern dependency, which affects error correction and requires costly column redundancy solutions.
Innovation Solution
A memory system that identifies weak strings or columns and uses a soft decision scheme to modify the weighting of data bits based on weak column information, employing algorithms like log-likelihood ratio calculations to improve error detection and correction without relying on column redundancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of bits stored in one memory cell is increased to achieve higher capacity, then storage capacity is improved, but data reliability deteriorates
Solution Approach 1:
The patent performs preliminary testing of memory strings during manufacturing to identify weak strings before the device is deployed. The identities of these weak strings are stored as weak column information, which is then used during error correction operations to apply modified weighting to data bits from these strings, thereby proactively addressing reliability issues in high-capacity MLC devices
Solution Approach 2:
The patent applies different error correction weighting strategies to different data bits based on their source. Data bits from identified weak strings are given reduced weighting in the error correction algorithm, while data bits from strong strings maintain standard weighting. This localized differentiation allows the system to maintain high storage capacity while compensating for reliability issues in specific memory regions
2Quantity of substance
If the number of memory cells integrated in the same area is increased to achieve higher density, then storage capacity is improved, but data reliability deteriorates
Solution Approach 1:
The system performs preliminary characterization of memory strings during manufacturing to identify weak strings before high-density operation begins. The weak column information obtained from this preliminary testing is stored and used during error correction to apply modified weighting to data bits from weak strings, enabling the high-density device to maintain reliability despite increased integration
Solution Approach 2:
The patent changes the weighting parameter in the error correction algorithm based on the source of the data bit. Data bits from weak strings (identified through preliminary testing) are assigned reduced weighting factors, while data bits from strong strings use standard weighting. This dynamic parameter adjustment allows the high-density memory to compensate for variability introduced by increased integration
3Reliability
If column redundancy is used to improve error correction capability, then data reliability is improved, but device complexity and cost increase
Solution Approach 1:
Instead of applying uniform column redundancy or error correction weighting to all data bits, the patent applies differentiated weighting based on the specific characteristics of each memory string. Data bits from weak strings (identified through preliminary testing) receive reduced weighting in the error correction algorithm, while data bits from strong strings maintain standard weighting. This localized approach improves error correction effectiveness without requiring additional redundant columns
Solution Approach 2:
The system uses information about weak strings (weak column information) that is already obtained during manufacturing testing to improve error correction capability. Rather than requiring additional redundant columns or complexity, the system leverages existing characterization data to dynamically adjust error correction weighting, allowing the memory device to self-optimize its error correction based on its own measured characteristics
Data Source
AI summary
Methods of operating nonvolatile memory devices include testing strings of nonvolatile memory cells in the memory device to identify at least one weak string therein having a higher probability of yielding erroneous read data error relative to other strings. An identity of the at least one weak string may be stored as weak column information, which may be used to facilitate error detection and correction operations. In particular, an error correction operation may be performed on bits of data read from the strings using an algorithm that modifies a weighting of the reliability of one or more data bits in the bits of data based on the weak column information. More specifically, an algorithm may be used that interprets a bit of data read from the at least one weak string as having a relatively reduced reliability relative to other ones of the data bits.