Semiconductor Memory Device Multilevel Data Integrity
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Solution Overview
Problem
In NAND flash memory, the miniaturization of elements leads to increased influence of adjacent cell threshold voltages, causing data instability and destruction of previously written data during multivalued storage, especially when writing operations are interrupted.
Innovation Solution
A semiconductor memory device with a memory cell array and control section that manages threshold voltages through multiple write operations and flag cells to maintain data integrity by setting and verifying threshold voltages across multiple levels, preventing overlap and ensuring data retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multivalued data is stored in a single memory cell using multiple threshold voltages, then storage capacity is improved, but threshold voltage distribution control becomes more difficult due to adjacent cell influence
Solution Approach 1:
The write operation is segmented into multiple stages: first writing one-bit data to the memory cell, then writing to adjacent cells, and finally writing the remaining data to the original cell. This segmentation prevents threshold voltage overlap by completing intermediate write steps before proceeding to the next stage, thereby resolving the contradiction between storing multiple values and maintaining precise threshold voltage distribution.
2Productivity
If writing speed is increased by writing data directly to the memory cell, then productivity is improved, but data destruction occurs when writing is interrupted due to overlapping threshold voltage distributions
Solution Approach 1:
The method performs preliminary write actions in a specific sequence: first writing to the memory cell, then to adjacent cells, and finally to the original cell again. This preliminary action structure ensures that threshold voltage distributions do not overlap, preventing data destruction even if writing is interrupted, while maintaining efficient write speed.
3Volume of moving object
If element size is reduced for miniaturization, then device density is improved, but adjacent cell threshold voltage influence increases causing data instability
Solution Approach 1:
The write operation is divided into distinct segments that address adjacent cells separately from the target cell. By segmenting the write process into steps that complete adjacent cell writes before returning to the target cell, the method isolates the harmful adjacent cell influence and prevents it from corrupting the stored data, enabling continued miniaturization without sacrificing data stability.
Data Source
AI summary
A plurality of memory cells each storing n values (n is a natural number which is not smaller than 3) are arranged in a matrix form in a memory cell array, and each memory cell is connected with a word line and a bit line. Each memory cell stores the n-valued data by a first write operation and a second write operation. A read section sets a potential of a word line, and reads data from a memory cell in the memory cell array. If data read by the read section and written in the second write operation includes an uncorrectable error, a control section changes a potential of a word line supplied to the read section when reading data written in the first write operation.