Flash Memory Read Voltage Calibration for Error Reduction
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Solution Overview
Problem
The manufacturing process variations in flash memory devices lead to shifts in critical voltage distribution, making it difficult to accurately identify storage states and resulting in error bits.
Innovation Solution
A read voltage setting method that programs data into memory cells, determines a default read voltage based on the critical voltage distribution, adjusts test read voltages to minimize error bits, and records the optimized read voltage adjustment values for each word line, allowing for correct identification of storage states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed read voltage is used for reading data from memory cells, then the reading operation is simple and fast, but manufacturing process variations cause shifts in critical voltage distribution leading to inaccurate identification of storage states and error bits
Solution Approach 1:
The patent applies preliminary action by determining optimized read voltages in advance during a voltage calibration process. The controller performs sweep operations to identify critical voltage distributions and establishes lookup tables storing optimized read voltages for different word lines before normal read operations. This preliminary calibration eliminates the need for real-time voltage adjustments during data reading, maintaining operational simplicity while achieving high measurement precision through pre-determined voltage settings that account for manufacturing variations.
Solution Approach 2:
The patent implements dynamics by transitioning from a fixed read voltage approach to a dynamic, adaptive voltage selection mechanism. The system determines optimized read voltages based on actual critical voltage distributions measured during calibration, and these voltages are stored in lookup tables for different word lines. During read operations, the controller dynamically selects the appropriate read voltage from the lookup table based on the specific word line being accessed, allowing the system to adapt to manufacturing variations while maintaining fast operation speeds.
2Ease of manufacture
If the critical voltage distribution shifts due to manufacturing variations, then manufacturing cost and process flexibility are maintained, but the storage state identification accuracy deteriorates resulting in error bits
Solution Approach 1:
The patent applies feedback by implementing a voltage calibration process that measures the actual critical voltage distribution of memory cells and uses this information to determine optimized read voltages. The controller performs sweep operations to identify the distribution characteristics and adjusts the read voltages accordingly. This feedback mechanism ensures that even when manufacturing variations cause shifts in critical voltage distribution, the system automatically adapts by selecting read voltages that match the actual device characteristics, thereby maintaining high data accuracy without compromising manufacturing flexibility.
Solution Approach 2:
The patent implements parameter changes by adjusting the read voltage parameter based on the measured critical voltage distribution. Instead of using a fixed read voltage, the system determines optimized read voltages that account for manufacturing variations. The controller modifies the read voltage parameter dynamically based on the specific word line and its corresponding critical voltage characteristics, allowing the system to maintain high reliability across different manufacturing batches while preserving ease of manufacture through a standardized calibration procedure.
Data Source
AI summary
A read voltage setting method for a rewritable non-volatile memory module is provided. The method includes: reading test data stored in memory cells of a word line to obtain a corresponding critical voltage distribution and identifying a default read voltage corresponding to the word line based on the corresponding critical voltage distribution; applying a plurality of test read voltages obtained according to the default read voltage to the word line to read a plurality of test page data; and determining an optimized read voltage corresponding to the word line according to the minimum error bit number among a plurality of error bit numbers of the test page data. The method further includes calculating a difference value between the default read voltage and the optimized read voltage as a read voltage adjustment value corresponding to the word line and recording the read voltage adjustment value in a retry table.