Memory Cell Threshold Voltage Window Extension via Cross-Coupling
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Solution Overview
Problem
NAND flash memory faces challenges with reduced charge storage capacity and increased floating gate coupling between memory cells, leading to a reduced effective threshold voltage window, which affects programming reliability and efficiency.
Innovation Solution
The technology utilizes cross-coupling effects to extend the effective threshold voltage window of a memory cell by splitting programming states into substates, allowing additional information to be embedded within this extended window, thereby improving programming performance, read performance, and reducing memory cell array size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If process geometries are shrunk to reduce cost per bit, then manufacturing cost decreases, but charge storage capacity per memory cell and effective threshold voltage window are reduced
Solution Approach 1:
The patent changes the parameter space by utilizing negative threshold voltage regions and extending the voltage window beyond traditional positive thresholds. By programming memory cells to achieve negative threshold voltages and using extended voltage ranges, the system compensates for the reduced effective window caused by scaling, maintaining reliability while benefiting from smaller geometries
Solution Approach 2:
The patent introduces an additional dimension to the threshold voltage spectrum by utilizing negative voltage values. Instead of only increasing positive threshold voltages, the system extends the voltage window in both positive and negative directions, effectively doubling the available programming states and compensating for scaling-induced window reduction
2Quantity of substance
If floating gate coupling between adjacent memory cells increases due to scaling, then device density increases, but programming reliability deteriorates
Solution Approach 1:
The patent converts the harmful floating gate coupling effect into a beneficial mechanism by using cross-coupling techniques. Neighbor cell states are deliberately utilized to extend the effective voltage window of target cells, transforming the interference caused by coupling into an extended programming range that improves reliability
Solution Approach 2:
The system implements feedback by sensing the states of neighboring memory cells and using this information to adjust the programming of target cells. The cross-coupling effect is measured and utilized to extend the voltage window dynamically, allowing the system to adapt to the actual coupling conditions and maintain programming reliability
3Ease of operation
If traditional voltage window programming is used, then programming simplicity is maintained, but programming speed and data retention are insufficient
Solution Approach 1:
The patent segments the programming process into multiple passes, including a first pass that programs cells to intermediate states and a second pass that completes programming to final states. This segmentation allows for more careful, reliable programming that improves data retention while maintaining reasonable programming speed through parallel processing of multiple cells
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 enhances programming speed, read performance, and data retention while reducing memory costs by utilizing the extended threshold voltage window for error correction and redundancy, allowing for more efficient data storage and retrieval.
Implementation Method 1
The amount of charge on the floating gate is typically controlled using Fowler-Nordheim tunneling or hot-electron injection
Implementation Method 2
The amount of charge on the floating gate is typically controlled using Fowler-Nordheim tunneling or hot-electron injection
Data Source
AI summary
Methods for operating a non-volatile storage system in which cross-coupling effects are utilized to extend the effective threshold voltage window of a memory cell and to embed additional information within the extended threshold voltage window are described. In some cases, additional information may be embedded within a memory cell storing the highest programming state if the memory cell is in a high boosting environment by splitting the highest programming state into two substates and programming the memory cell to one of the two substates based on the additional information. A memory cell may be in a high boosting environment if its neighboring memory cells are in a high programmed state. Additional information may also be embedded within a memory cell storing the lowest programming state if the memory cell is in a low boosting environment. The additional information may include error correction information.