Flash Memory Read Retry Using ECC and Adaptive Read Voltages
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Solution Overview
Problem
As flash memory systems are scaled down and the number of bits stored in each memory cell increases, the read margin between program states decreases, leading to frequent read errors, and existing methods struggle to correct these errors quickly and precisely.
Innovation Solution
The method involves reading multi-bit nonvolatile memory cells using multiple sets of read voltages, performing ECC decoding operations on the resulting data, and updating a read retry table based on error analysis to select the most accurate read data, with the option to retry reads using different voltages to minimize errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of bits stored in each memory cell is increased, then storage density is improved, but read margin between program states decreases leading to frequent read errors
Solution Approach 1:
The patent performs preliminary ECC decoding operations on first read data before finalizing the read result. By decoding the first read data obtained with initial read voltages and evaluating the decoding results, the system proactively identifies and corrects errors before they propagate, thereby maintaining high read reliability despite increased storage density
Solution Approach 2:
The patent dynamically adjusts read voltages based on wear information and decoding results. When read errors are detected or wear level increases, the system changes the read voltage parameters to optimize the read margin, allowing reliable reading even as storage density increases and margins decrease
2Reliability
If multiple read voltages are used to improve read accuracy, then read reliability is improved, but read time and processing complexity increase
Solution Approach 1:
The patent performs ECC decoding operations on first read data in advance, before determining whether second read voltages are needed. This preliminary decoding allows the system to quickly identify clearly readable data and avoid unnecessary second reading operations, reducing overall read time while maintaining accuracy
Solution Approach 2:
The system uses the ECC decoding results of the first read data to automatically determine whether second reading is necessary. By self-evaluating the quality of the first read through decoding metrics, the system avoids blanket re-reading and only performs second reading when actually needed, optimizing the balance between accuracy and speed
3Reliability
If ECC decoding operations are performed on multiple sets of read data, then error correction capability is improved, but processing complexity increases
Solution Approach 1:
The patent performs ECC decoding on first read data as a preliminary step before deciding whether to read with second voltages. This initial decoding provides early error detection and reduces the need for complex multi-stage decoding by identifying cases where simple first reading suffices
Solution Approach 2:
The system automatically evaluates the ECC decoding results and uses this information to control whether second reading and decoding are necessary. The decoding results themselves drive the control logic, eliminating the need for external complex control mechanisms and simplifying the overall processing architecture
Data Source
AI summary
Methods of operating nonvolatile memory devices include reading a first plurality of multi-bit nonvolatile memory cells in the nonvolatile memory device using a first plurality of read voltages to thereby generate first read data, and then rereading the first plurality of multi-bit nonvolatile memory cells using a second plurality of read voltages that differ, at least in part, from the first plurality of read voltages, to thereby generate second read data. An operation is then undertaken to perform first and second ECC decoding operations on the first and second read data, respectively, to thereby identify whether the first read data or the second read data more accurately reflects data stored in the first plurality of multi-bit nonvolatile memory cells during the reading and rereading.