Memory Controller Data Pattern Control for NAND Flash Reliability
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Solution Overview
Problem
The increasing integration density in non-volatile memory devices, such as NAND flash memory, leads to proximity issues between memory cells, causing data degradation due to coupling effects like electric field coupling, which adversely affect data reliability.
Innovation Solution
A method and system involving a memory controller that generates a coset representative sequence, performs XOR operations, calculates branch metrics, and determines survivor paths to control data programming patterns, thereby minimizing undesirable coupling effects and enhancing data reliability by defining appropriate programmed states for memory cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If integration density is increased to improve storage capacity, then productivity is improved, but coupling effects between adjacent memory cells worsen data reliability
Solution Approach 1:
The patent applies preliminary action by pre-defining favorable and unfavorable programmed states before data programming occurs. The memory controller identifies unfavorable state patterns (e.g., adjacent cells both in erased state or both in highest programmed state) and proactively adjusts programming to avoid these patterns, thereby preventing coupling effects before they degrade data reliability.
Solution Approach 2:
The patent changes the parameter distribution of programmed states by constraining certain bit lines from transitioning to unfavorable states (erased or highest programmed state). This parameter control modifies the threshold voltage distribution to widen separation between states, reducing overlap and improving reliability despite high integration density.
2Ease of operation
If data programming pattern is not properly defined, then ease of operation is improved, but coupling effects worsen and cause data degradation
Solution Approach 1:
The memory controller performs self-service by automatically analyzing incoming data patterns and adjusting programmed states to avoid unfavorable configurations. The system autonomously identifies patterns that would cause coupling effects and modifies the programming operation without requiring external intervention, thereby maintaining both ease of operation and data reliability.
3Manufacturing precision
If threshold voltage distribution is narrowed, then manufacturing precision is improved, but coupling effects worsen and reduce data reliability
Solution Approach 1:
The patent applies local quality by treating different bit lines differently based on their programmed states. Certain bit lines are constrained from transitioning to unfavorable states (erased or highest programmed state) while others are allowed greater flexibility. This localized control creates favorable threshold voltage distributions that widen separation between states, improving reliability without sacrificing manufacturing precision.
Data Source
AI summary
A method of operating a memory controller includes receiving a first data sequence and generating a coset representative sequence that can be divided into m-bit strings, where “m” is a natural number of at least 2; performing a first XOR operation on each of the m-bit strings in the coset representative sequence and binary bits; calculating all possible branch metrics according to a result of the first XOR operation; determining a survivor path sequence based on the all possible branch metrics; and performing a second XOR operation on the coset representative sequence and the survivor path sequence and generating an output sequence.