Adaptive Read Voltage Adjustment for Flash Memory Cell State Identification
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Solution Overview
Problem
Flash memory devices experience storage state inaccuracies due to electron injection and removal during writing and erasing operations, leading to error bits as the distribution of threshold voltage shifts, making it difficult to identify the correct storage state of memory cells over time.
Innovation Solution
A data reading method that determines a first read voltage based on the critical voltage distribution of memory cells and applies adjustment read voltages to correctly identify and decode the storage state, using a set of read voltages that include positive and negative adjustments to account for normal, right-offset, or left-offset distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If frequent writing and erasing operations are performed to meet storage demands, then productivity is improved, but the flash memory device deteriorates and threshold voltage distribution shifts, worsening measurement precision
Solution Approach 1:
The patent applies dynamics by making the read voltage adaptive rather than fixed. The memory controller dynamically adjusts the read voltage based on the detected threshold voltage distribution characteristics (normal, right-offset, or left-offset). This allows the system to maintain accurate data reading despite the shifting threshold voltage distribution caused by wear from frequent write/erase operations.
Solution Approach 2:
The patent changes the parameter of read voltage to resolve the contradiction. By detecting the threshold voltage distribution type and selecting different read voltages accordingly (higher voltage for right-offset, lower voltage for left-offset), the system compensates for the degradation effects of frequent operations while maintaining measurement precision.
2Duration of action of stationary object
If the threshold voltage distribution shifts due to wear, then the memory device continues to operate, but the storage state identification becomes inaccurate, worsening reliability
Solution Approach 1:
The patent implements feedback by having the memory controller detect the threshold voltage distribution characteristics and use this information to adjust the read voltage. This closed-loop approach ensures that even as the memory device operates for extended periods and accumulates wear, the system continuously adapts to maintain accurate storage state identification, thereby preserving reliability throughout the device's operational life.
Solution Approach 2:
The system transitions from static read voltage to dynamic read voltage adjustment based on real-time detection of threshold voltage distribution. This allows the memory device to maintain reliable operation over its entire lifespan despite the progressive degradation from frequent write/erase cycles.
3Device complexity
If a fixed read voltage is used for reading memory cells, then device complexity is reduced, but measurement precision deteriorates when threshold voltage distribution shifts
Solution Approach 1:
The patent introduces dynamic voltage adjustment based on detected distribution characteristics. The memory controller detects whether the threshold voltage distribution is normal, right-offset, or left-offset, and automatically selects the appropriate read voltage. This adds minimal complexity to the reading operation while significantly improving measurement precision under varying conditions.
Solution Approach 2:
The read voltage parameter is changed based on the detected threshold voltage distribution type. By implementing a simple detection mechanism that identifies the distribution characteristic and adjusts the read voltage accordingly, the system achieves high measurement precision without substantially increasing device complexity.
Data Source
AI summary
A data reading method for a rewritable non-volatile memory module is provided. The method includes determining a corresponding read voltage based on a critical voltage distribution of memory cells of a word line. The method further includes: if the critical voltage distribution of the memory cells is a right-offset distribution, applying a set of right adjustment read voltage to the word line to read a plurality of bit data as corresponding soft values; and decoding the corresponding soft values to obtain page data stored in the memory cells. Herein, the set of right adjustment read voltage includes a plurality of positive adjustment read voltages and a plurality of negative adjustment read voltages and the number of the positive adjustment read voltages is more than the number of the negative adjustment read voltages. Accordingly, storage states of the memory cells can be identified correctly.