Composite Read Generation for NAND Flash Capacitive Coupling
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Solution Overview
Problem
Capacitive coupling in NAND Flash devices, where writing to one cell affects adjacent cells, becomes exacerbated as device geometry decreases, leading to errors in data retrieval due to increased interference between floating-gate cells.
Innovation Solution
A process and system for generating composite reads by using multiple read thresholds and neighboring cell data to selectively combine raw read values, reducing the impact of capacitive coupling and improving error correction decoding success rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If NAND Flash process geometry is reduced to increase storage density, then storage capacity is improved, but capacitive coupling between adjacent cells is exacerbated leading to increased read errors
Solution Approach 1:
The patent applies preliminary action by reading neighboring cells before reading the target cell. The read values from neighboring cells are obtained first and used to generate compensation values that are then applied to correct the target cell read values. This preliminary reading and compensation generation eliminates the harmful capacitive coupling effects before they corrupt the data retrieval process.
Solution Approach 2:
The patent converts the harmful capacitive coupling effect into a beneficial compensation mechanism. By measuring the read values from neighboring cells that have been affected by capacitive coupling, the system calculates compensation values that represent the coupling effect. These compensation values are then subtracted from the target cell read values, transforming the previously harmful coupling effect into a correctable distortion that improves overall data accuracy.
2Measurement precision
If multiple read thresholds and composite read generation are used to correct capacitive coupling effects, then data retrieval accuracy is improved, but processing complexity is increased
Solution Approach 1:
The patent applies segmentation by dividing the read process into distinct stages: reading neighboring cells, generating compensation values based on those readings, and applying compensation to target cell readings. This segmentation allows the complex error correction to be broken into manageable steps that can be implemented efficiently in hardware or firmware without overwhelming processing complexity.
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
The composite read generation technique enhances the accuracy of data retrieval by accounting for capacitive coupling effects, improving the chances of successful error correction decoding and reducing read errors in NAND Flash devices.
Implementation Method 1
Capacitive coupling is an issue in NAND Flash where the writing of a cell (accomplished by injecting charge onto the floating-gate of a cell) adds charge to the floating-gates of one or more adjacent cells.
Data Source
AI summary
A victim group of one or more cells is read using a first read threshold to obtain a first raw read which includes one or more values. The victim group of cells is read using a second read threshold to obtain a second raw read which includes one or more values. A neighboring read, corresponding to a neighboring group of one or more cells associated with the victim group of cells, is obtained. A composite read is generated, including by selecting from at least the first raw read and the second raw read based at least in part on the neighboring read.