NAND Flash Verify Operation Using Distinct Unselected Word Line Voltages
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Solution Overview
Problem
The back pattern effect in NAND flash memory devices leads to errors during data reading due to changes in channel resistance and IV characteristics after programming, caused by uneven programming of memory cells, resulting in artificial shifts of threshold voltages.
Innovation Solution
Applying distinct voltages to unselected word lines that have been programmed versus those that have not been programmed, along with neighboring memory cells, during verify and read operations to maintain accurate threshold voltage measurements and reduce errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a single voltage is applied to all unselected word lines during verify operations, then the operation is simple, but the threshold voltage measurements become inaccurate due to the back pattern effect
Solution Approach 1:
The patent applies different voltages to different groups of unselected word lines based on their programming status. Specifically, unselected word lines that have been programmed receive a first voltage, while unselected word lines that have not been programmed receive a second voltage. This local differentiation eliminates the back pattern effect and ensures accurate threshold voltage measurements during verify operations.
2Productivity
If memory cells are programmed in sequence from source side to drain side, then the programming process is systematic, but the IV characteristics change during verification causing errors
Solution Approach 1:
The patent dynamically adjusts the voltage applied to unselected word lines based on their programming status. During the sequential programming process, the system identifies which unselected word lines have been programmed and applies appropriate voltages accordingly. This dynamic adaptation maintains consistent IV characteristics throughout the programming process, ensuring reliable data sensing even as the programming progresses.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach minimizes errors by maintaining consistent IV characteristics and accurate threshold voltage readings, ensuring reliable data sensing and reading operations in NAND flash memory systems.
Implementation Method 1
Applying distinct voltages to unselected word lines that have been programmed versus those that have not been programmed, along with neighboring memory cells, during verify and read operations to maintain accurate threshold voltage measurements and reduce errors
Data Source
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AI summary
When performing a data sensing operation, including a verify operation during programming of non-volatile storage elements (or, in some cases, during a read operation after programming), a first voltage (Vrdl) is used for unselected word lines (464, 466, 468) that have been subjected to a programming operation and a second voltage (Vrd2) is used for unselected word lines (472, 474, 476, 478) that have not been subjected to a programming operation. In some embodiments, the second voltage is lower than the first voltage.