Flash Memory Encoding for Lateral Charge Spreading
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Solution Overview
Problem
Flash memory devices face challenges in reducing the width of threshold voltage distribution in multi-bit cells, leading to increased read-failure rates due to overlapping voltage distributions and lateral charge spreading, which contaminates data over time.
Innovation Solution
A memory device with an encoder that generates codewords with specific maximum and minimum values of successive ones and zeros, and a programming unit that programs these codewords to multi-bit cells, using encoding schemes like Run Length Limited (RLL) codes to reduce lateral charge spreading and threshold voltage distribution width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If data is programmed to multi-bit cells using conventional encoding, then storage capacity is increased, but threshold voltage distribution width increases leading to read failures
Solution Approach 1:
The patent applies Run Length Limited (RLL) encoding to transform the data pattern before programming. This changes the parameter of data sequence composition by limiting the maximum number of successive identical bits (e.g., maximum 2 successive ones and 2 successive zeros). This parameter transformation reduces threshold voltage distribution width and prevents overlapping between programmed and erased states, thereby reducing read failure rates while maintaining multi-bit storage capacity
2Quantity of substance
If data is programmed to multi-bit cells, then storage density is increased, but lateral charge spreading contaminates data
Solution Approach 1:
RLL encoding transforms the data pattern to limit successive identical bits, which reduces the intensity of lateral charge spreading between adjacent memory cells. By controlling the maximum run length of identical bits, the patent minimizes charge contamination to neighboring cells while maintaining high storage density in multi-bit cells
3Device complexity
If conventional encoding is used for data pages, then encoding simplicity is maintained, but transmission errors increase
Solution Approach 1:
The patent applies RLL encoding with specific parameters (maximum successive ones and zeros) to data pages before programming. This parameter-based transformation provides reference information for Phase Locked Loops (PLL) during transmission, reducing synchronization errors and improving reliability while adding manageable encoding complexity
Data Source
AI summary
Example embodiments may provide a memory device and memory data programming method. The memory device according to example embodiments may encode a first data page to generate at least one first codeword and encode a second data page to generate a second codeword. The memory device may generate the first codeword with at least one of a maximum value of a number of successive ones and a second maximum value of a number of successive zeros. The memory device may program the at least one first codeword and the at least one second codeword to a plurality of multi-bit cells.