Nonvolatile Memory Read Voltage Adjustment for Data Integrity
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Solution Overview
Problem
In nonvolatile semiconductor memory devices, particularly flash memory devices, the variation in threshold voltages of multi-level cells over time and temperature leads to data integrity issues, requiring adjustments in read voltages to accurately identify data states, which existing methods fail to address efficiently.
Innovation Solution
A read method and storage device that adjusts read voltages based on the number of logical 0s or 1s, or the ratio of logical 1s to 0s in the data, using a memory controller to decide a second read voltage when errors are uncorrectable, allowing for error correction and optimal read voltage determination without additional sensing operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If read voltages are adjusted to identify data states in multi-level cells, then data integrity is improved, but read time increases due to multiple sensing operations
Solution Approach 1:
The patent applies preliminary action by performing a first sensing operation to obtain initial read data before the final read operation. This preliminary sensing allows the system to evaluate data quality and determine whether a second sensing operation is necessary, thereby avoiding unnecessary additional sensing steps and reducing overall read time while maintaining data integrity.
Solution Approach 2:
The patent implements feedback by evaluating the read data from the first sensing operation to determine whether a second sensing operation with adjusted read voltage is needed. The system uses error detection and data characteristics (such as distribution valley detection) to provide feedback that controls whether to proceed with additional sensing, thus optimizing the balance between data integrity and read time.
2Reliability
If multiple read voltages are used to sense data for error correction, then data reliability is improved, but device complexity increases
Solution Approach 1:
The patent applies dynamics by making the sensing operation adaptive rather than fixed. The system dynamically determines whether to perform a second sensing operation based on the evaluation of data from the first sensing operation. This dynamic approach allows the system to use multiple read voltages only when necessary, reducing operational complexity while maintaining data reliability.
Solution Approach 2:
The patent implements parameter changes by adjusting the read voltage based on detected errors or data characteristics. When the first sensing operation detects issues such as uncorrectable errors or specific data distribution patterns, the system changes the read voltage parameter for a second sensing operation, thereby improving data reliability without requiring permanently complex multi-voltage sensing infrastructure.
3Measurement precision
If read voltages are adjusted based on threshold voltage variations, then measurement precision is improved, but the number of operations increases
Solution Approach 1:
The patent applies partial action by performing only one or two sensing operations instead of systematically performing multiple sensing operations with different read voltages. The system performs a first sensing operation and selectively performs a second sensing operation only when evaluation of the first results indicates it is necessary, thereby achieving adequate measurement precision without excessive operations.
Solution Approach 2:
The patent uses preliminary sensing to gather information about data quality and threshold voltage distribution before deciding whether additional precise measurements are needed. This preliminary action allows the system to achieve measurement precision adaptively, performing detailed threshold voltage identification only when the preliminary evaluation indicates it will improve the result.
Data Source
AI summary
A read method of a nonvolatile memory device includes reading data from a selected memory area of the nonvolatile memory device according to a first read voltage; detecting and correcting an error of the read data; and deciding a second read voltage for reading the selected memory area when an error of the read data is uncorrectable. The second read voltage is decided according to either the number of logical 0s or 1s included in the read data, or a ratio of logical 1s to logical 0s in the read data.