TVS Pattern Segmentation for Memory Cell Data Storage
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Solution Overview
Problem
As newer memory technologies, such as 3D quad-level cell NAND flash memory, become more sensitive to retention and program-erase cycling effects, there is a need for an efficient storage technique to manage the increasing number of threshold voltage shift (TVS) values required to maintain low residual bit-error rates.
Innovation Solution
The method involves obtaining a plurality of TVS patterns, each containing N−1 TVS reference values, and performing an assignment routine to store a reference to a matching TVS pattern and the TVS residual values for each set of memory cells. This allows for efficient storage and retrieval of TVS values, reducing memory consumption and processing resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple TVS values are stored to maintain low residual bit-error rates in newer memory technologies, then reliability is improved, but memory consumption and device complexity increase
Solution Approach 1:
The patent segments the storage of TVS values by dividing memory cells into groups based on their physical conditions (e.g., retention characteristics, P/E cycle counts). Each group is assigned a representative TVS pattern, and only the residual values for that group need to be stored, rather than storing complete TVS values for all cells individually. This segmentation reduces the total memory consumption while maintaining reliability.
Solution Approach 2:
The patent uses TVS patterns as templates or copies that represent typical threshold voltage shift behavior for specific physical conditions. Instead of storing actual TVS values for each cell, the system stores references to these patterns and only the residual deviations. This copying approach significantly reduces storage requirements while preserving the necessary information for accurate read operations.
2Manufacturing precision
If the number of threshold voltages to be tracked increases with higher memory cell complexity, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent merges the tracking of multiple individual TVS values into a unified approach by using TVS patterns that capture the collective behavior of threshold voltages for cells with similar physical conditions. Instead of tracking N-1 individual TVS values separately for each cell, the system tracks a compact representation (pattern reference + residuals) that applies to multiple cells simultaneously, reducing device complexity while maintaining precision.
Solution Approach 2:
The patent changes the representation parameters from storing complete TVS value sets to storing pattern references and residual values. This parameter transformation reduces the amount of data that needs to be managed and processed, thereby reducing device complexity while preserving the manufacturing precision required for accurate threshold voltage tracking in multi-level cells.
Data Source
AI summary
The invention relates to a method of operating a memory device comprising memory cells for storing information on N voltage levels separated by N−1 threshold voltages, the method comprising: obtaining a plurality of threshold voltage shift (TVS) patterns, each comprising N−1 TVS reference values representing expected shifts of the threshold voltages of a set of memory cells having a specific physical condition; assigning a matching TVS pattern to the set of memory cells; storing differences between actual TVS values of the memory cells and corresponding TVS reference values of the matching TVS pattern as TVS residual values; upon a reading instruction for a specified memory cell, determining restored TVS values by combining the matching TVS pattern of the corresponding set of memory cells with corresponding TVS residual values; and reading the information from the specified cell using the restored TVS values.