3D NAND Memory String Write-After-Read for Data Retention
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Solution Overview
Problem
In memory systems, particularly 3D NAND flash, the program state difference between adjacent memory cells leads to significant electron lateral migration, resulting in poor data retention performance of edge word lines when data is not fully written, affecting data accuracy over time.
Innovation Solution
Implement a write-after-read operation where data from a memory cell on an edge word line is read and then immediately written to an adjacent cell that has not been written to, ensuring both cells are in the same program state, thereby suppressing electron lateral migration and enhancing data retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is written to memory cells in a memory block, then storage capacity is utilized, but electron lateral migration occurs between adjacent memory cells with different program states, degrading data retention performance
Solution Approach 1:
The patent applies preliminary action by performing a write-after-read operation where data is first read from the first memory cell and then immediately written to the second memory cell before any significant electron lateral migration can occur. This preliminary data transfer ensures both cells are in the same program state, preventing the harmful electron migration effect from degrading data retention performance.
2Reliability
If edge word lines are not fully written with data, then storage resources are saved, but data retention performance deteriorates due to electron migration from adjacent cells
Solution Approach 1:
The patent performs a write-after-read operation as a preliminary action to transfer data from the first memory cell to the second memory cell. This ensures that even edge word lines that are not fully written with data are protected by having adjacent cells in the same program state, thereby maintaining data retention performance while allowing flexible storage resource utilization.
3Reliability
If a write-after-read operation is performed to suppress electron lateral migration, then data retention performance is improved, but additional write operations are required
Solution Approach 1:
The patent implements a write-after-read operation as a preliminary action that reads data from the first memory cell and immediately writes it to the second memory cell. This sequence of operations, while adding complexity to the operation sequence, is performed at a low level to suppress electron lateral migration and ensure data retention performance without requiring complex external intervention.
Data Source
AI summary
The present application provides a memory system, a method for operating the memory system, a controller and a storage medium. The memory system includes: a memory device and a controller; the controller is configured to send a read command to the memory device; the memory device is configured to read data stored in a first memory cell in the memory device according to the read command; the first memory cell and the second memory cell are located in the same memory string; the second memory cell is a memory cell that has not yet been written with data; the controller is further configured to send a write command to the memory device; the memory device is further configured to write data read from the first memory cell to the second memory cell according to the write command.