Flash Memory Read Voltage Adjustment for Data Reliability
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Solution Overview
Problem
The reliability of read data in flash memory devices is compromised due to variations in threshold voltages of memory cells, leading to increased bit error rates and reduced ECC error correction efficiency, especially when threshold voltage distributions overlap.
Innovation Solution
A method involving a voltage generator that applies sequential read voltages to count memory cells within specific voltage ranges, comparing their counts to determine optimal read voltages, thereby adjusting the read voltage levels to minimize bit error rates and improve ECC error correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed read voltage is used for reading memory cells, then the read operation is simple and fast, but the reliability of read data deteriorates due to threshold voltage variations
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed read voltage to a dynamic read voltage that is adjusted based on the counted number of memory cells in different threshold voltage ranges. The read voltage is modified according to the distribution characteristics of memory cells, allowing the system to adapt to threshold voltage variations and improve read data reliability.
Solution Approach 2:
The patent changes the read voltage parameter based on the counted distribution of memory cell threshold voltages. By determining the number of memory cells in specific voltage ranges and using this information to adjust the read voltage, the system optimizes the voltage parameter to match the actual memory cell characteristics, thereby improving reliability without excessive complexity.
2Reliability
If multiple read voltages are applied to count memory cells and determine optimal read voltage, then the reliability of read data is improved, but the operation time increases
Solution Approach 1:
The patent applies preliminary action by performing a counting operation to determine the distribution of memory cell threshold voltages before the actual read operation. This preliminary characterization allows the system to pre-determine the optimal read voltage, avoiding the need for multiple trial read operations and reducing overall read time while improving reliability.
Solution Approach 2:
The patent uses feedback from the counting operation to adjust the read voltage. The number of memory cells counted in different voltage ranges provides feedback information that is used to determine the optimal read voltage, creating a closed-loop system that optimizes both reliability and time efficiency.
3Reliability
If read voltage is adjusted based on memory cell threshold voltage distribution, then bit error rate is reduced, but the complexity of voltage control increases
Solution Approach 1:
The patent segments the threshold voltage distribution into multiple voltage ranges and counts the number of memory cells in each range. This segmentation allows the system to understand the distribution characteristics and adjust the read voltage accordingly, reducing bit error rates while maintaining manageable control complexity through structured analysis of voltage distributions.
Data Source
AI summary
An operating method for a non-volatile memory device includes applying first and second read voltages to a first word line to perform a read operation; counting first memory cells each having a threshold voltage belonging to a first voltage range between the first read voltage and the second read voltage; applying a third read voltage to the first word line sequentially after applying the second read voltage to count second memory cells each having a second threshold voltage belonging to a voltage range between the second read voltage and the third read voltage; comparing the number of first memory cells counted and the number of second memory cells counted; determining a fourth read voltage based on a result of the comparing; and applying the fourth read voltage to the first word line sequentially after applying the third read voltage.