Non-Volatile Memory Read Voltage Adjustment for Coupling Effects
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Solution Overview
Problem
Non-volatile memory devices, particularly NAND-type flash memory, face challenges in maintaining reliable read data due to threshold voltage shifts caused by coupling effects from adjacent cells, leading to overlapping distributions and increased error rates.
Innovation Solution
The method involves detecting threshold voltage variations in aggressor cells and assigning victim cells to specific sub-distributions based on the distance of these variations, using a memory controller to set read voltages that account for the physical influence, thereby classifying and mitigating the coupling effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If read voltage is applied to victim cells without considering aggressor cell influence, then read operation is simple and fast, but threshold voltage overlap causes increased error rates and reduced data reliability
Solution Approach 1:
The patent applies preliminary action by detecting threshold voltage variations of aggressor cells before reading victim cells. The memory controller identifies the state of aggressor cells and determines their influence on victim cells in advance, then selects appropriate read voltages accordingly. This preliminary detection and classification approach enables reliable victim cell reading while accounting for coupling effects without requiring complex real-time adjustments during the read operation.
2Reliability
If threshold voltage variation detection and sub-distribution assignment is implemented, then coupling effect is mitigated and read reliability improves, but additional detection and classification steps increase operation complexity
Solution Approach 1:
The patent applies segmentation by dividing the threshold voltage distribution into multiple sub-distributions based on aggressor cell influence. Victim cells are classified into different sub-distributions (e.g., first sub-distribution for cells influenced by aggressors in erase state, second sub-distribution for cells influenced by aggressors in program state). This segmentation enables targeted selection of read voltages for each sub-distribution, improving reliability by accounting for coupling effects while maintaining efficient read operations through pre-defined voltage levels.
Data Source
AI summary
Disclosed is an access method of a non-volatile memory device which comprises detecting a threshold voltage variation of a first memory cell, the a threshold voltage variation of the first memory cell being capable of physically affecting a second memory cell; and assigning the second memory cell to a selected sub-distribution from among a plurality of sub-distributions according to a distance of the threshold voltage variation of the first memory cell, the plurality of sub-distributions corresponding to a target distribution of the second memory cell.