NAND Flash Memory Judgment Potential Correction Circuit
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Solution Overview
Problem
In NAND-type flash memory, the proximity effect caused by parasitic capacity between adjacent memory cells leads to threshold-value fluctuations, limiting the realization of fine multivalued memory due to tight distribution margins and increased fluctuations with miniaturization.
Innovation Solution
A nonvolatile semiconductor memory device with a judgment potential correction circuit that predicts and corrects threshold value shifts during readout, using a matrix-form memory cell array and specific write and readout circuits to eliminate the influence of proximity effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If memory cell size is reduced for miniaturization, then storage density is improved, but proximity effect increases causing threshold value fluctuations
Solution Approach 1:
The patent applies preliminary action by performing a read operation on adjacent memory cells before reading the target memory cell. This preliminary read captures the state of adjacent cells that will influence the target cell's threshold value through proximity effect. The captured information is then used to correct the judgment potential during the actual read, thereby compensating for the threshold fluctuation caused by miniaturization while maintaining high storage density.
2Quantity of substance
If threshold value distribution margin is reduced for multivalued memory, then storage capacity is improved, but readability deteriorates due to proximity effect
Solution Approach 1:
The patent implements feedback by using the read results from adjacent memory cells to dynamically adjust the judgment potential for reading the target memory cell. The correction circuit receives information about adjacent cell states and feeds this back to modify the read threshold, creating a closed-loop system that compensates for proximity effect-induced threshold shifts. This feedback mechanism enables reliable reading of multivalued data even with tight threshold distribution margins.
3Device complexity
If judgment potential is not corrected for proximity effect, then device complexity is reduced, but data misjudgment increases
Solution Approach 1:
The patent introduces an intermediary correction circuit that mediates between the simple read operation and the final data judgment. This intermediary component processes the raw read signals from both target and adjacent cells, applies the necessary potential corrections based on adjacent cell states, and then presents the corrected data for final interpretation. This intermediary approach maintains relative circuit simplicity while significantly improving data accuracy by isolating the complexity of proximity effect compensation in a dedicated correction stage.
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 allows for finer multivalued memory by correcting judgment potentials based on adjacent memory cells, expanding threshold value distributions and preventing data misjudgment, thereby enhancing data readability and storage precision.
Implementation Method 1
a threshold-value fluctuation of a read cell is generated by a parasitic capacity between floating gates of a memory cell (readout cell) as a readout object and a memory cell adjacent to this read-out cell
Data Source
AI summary
A nonvolatile semiconductor memory device is provided with a memory cell array, a judgment potential correction circuit, and a readout circuit. In the memory cell array, a plurality of memory cells are arranged in a matrix form, and the array includes a first memory cell as a readout object and a second memory cell disposed adjacent to the first memory cell. The judgment potential correction circuit corrects a judgment potential based on a threshold value of the second memory cell. The readout circuit reads the first memory cell as the readout object by use of the corrected judgment potential.