NAND Copyback Using Weak-Cell Classification to Cut ECC Delay
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Copyback operations in nonvolatile memory devices are prolonged due to error correction, leading to performance degradation.
Innovation Solution
Performing a copyback operation with internal classification of memory cells into normal and weak cells using different read and program voltage levels without external ECC, allowing efficient data storage in a destination area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If error correction operation is performed during copyback operation, then data reliability is improved, but operation time is increased
Solution Approach 1:
The copyback operation is segmented into two distinct paths: a fast path for normal memory cells that skips error correction, and a slow path for weak memory cells that performs error correction. This segmentation allows most data to be copied quickly while only correcting errors in problematic cells, thereby reducing overall operation time while maintaining data reliability.
Solution Approach 2:
Different read voltage levels are applied based on the local characteristics of memory cells. Normal memory cells use a first read voltage level for fast reading, while weak memory cells use a second read voltage level for accurate error detection. This local quality approach ensures that error correction is applied only where necessary, optimizing the balance between speed and reliability.
2Manufacturing precision
If classification of memory cells is performed, then data storage accuracy is improved, but operation complexity is increased
Solution Approach 1:
The patent changes the parameter of read voltage level based on memory cell characteristics. By adjusting the read voltage level (first level for normal cells, second level for weak cells), the system achieves accurate classification and storage without requiring complex physical modifications or additional hardware components, thus improving data storage accuracy while limiting complexity increases.
3Measurement precision
If different read voltage levels are used, then reading accuracy for weak cells is improved, but operation time is increased
Solution Approach 1:
The reading operation is segmented into two groups based on memory cell strength. Normal memory cells are read using a first read voltage level for fast operation, while weak memory cells are read using a second read voltage level for high accuracy. This segmentation ensures that the time penalty for high-accuracy reading is applied only to the minority of weak cells, not to all data operations.
Solution Approach 2:
The patent applies the higher accuracy second read voltage level only partially - specifically only to weak memory cells that require error correction - rather than applying it to all memory cells. This partial action approach achieves the necessary reading accuracy for problematic cells without incurring the time cost for all operations.
Data Source
AI summary
In performing a copyback operation, a copyback command for target data that are programmed in a source area based on first voltage levels is received. A hard data read operation and a soft data read operation are performed on the target data based on the copyback command. Memory cells in the source area are classified into normal memory cells and weak memory cells, based on results of the hard data read operation and the soft data read operation. A first copyback program operation in which first data among the target data are stored in a destination area is performed, based on second voltage levels. The first data correspond to the normal memory cells. A second copyback program operation in which second data among the target data are stored in the destination area is performed, based on third voltage levels. The second data correspond to the weak memory cells.