NAND Flash Memory Misplacement Mitigation Algorithm
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Solution Overview
Problem
Memory devices, particularly NAND flash devices, face issues with incorrect placement of threshold voltage during multi-level memory cell programming due to disturb mechanisms and cell defects, leading to misplacement errors that are not recoverable through conventional methods.
Innovation Solution
A dual pre-read method is implemented before the second programming pass to determine the number of memory cells with misplaced threshold voltages, allowing for suspension or continuation of the programming process based on a specified threshold, thereby mitigating misplacement errors and improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multi-level memory cell programming is performed using conventional methods, then memory storage capacity is increased, but misplacement errors occur due to disturb mechanisms and cell defects
Solution Approach 1:
The patent applies preliminary action by performing a dual pre-read operation before the second programming pass to identify cells with misplaced threshold voltages. This early detection allows the system to determine whether to proceed with or suspend the second programming pass, preventing further misplacement errors before they propagate through the programming process.
Solution Approach 2:
The patent implements feedback by using the results of the dual pre-read operation to control the subsequent programming process. The read data from the first and second read operations is compared, and based on the comparison results, the system provides feedback to decide whether to suspend or continue the second programming pass, thereby correcting or mitigating misplacement errors dynamically.
2Reliability
If dual pre-read method is implemented to detect misplaced cells, then misplacement errors are reduced, but programming time and process complexity increase
Solution Approach 1:
The patent applies partial action by performing reads on only the necessary portions of the memory array during the dual pre-read operation, rather than examining every cell. The system determines the number of misplaced cells and uses this information to selectively proceed with or suspend programming, applying just enough corrective action to mitigate errors without unnecessary overhead.
3Manufacturing precision
If dual pre-read operation is performed to identify misplaced cells, then threshold voltage placement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the programming process into distinct passes and separating the detection function from the programming function. The dual pre-read operation segments the verification step, allowing independent evaluation of threshold voltage placement before committing to the second programming pass, thereby managing complexity through structured process division.
Data Source
AI summary
A memory device comprises a memory array and a memory control unit. The memory includes multi-level memory cells. The memory control unit is configured to: initiate programming of memory cells of the memory array using a first pass programming operation, wherein the first pass programming operation places programming data using a first and second voltage threshold distributions; read programmed memory cells using a first read voltage level on word lines of the memory cells; read the programmed memory cells using a second read voltage level on the word lines of the memory cells; determine a number of the programmed memory cells with a voltage threshold placed between the first and second voltage threshold distributions by the programming; and suspend second pass programming of the memory cells in response to the determined number of cells exceeding a specified threshold number, and initiate a second pass programming operation otherwise.