Modified One-Hot WOM Codes for Flash Memory Wear Leveling
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Solution Overview
Problem
Current digital memory technologies face limitations in achieving high cell sum-rates and extending the lifecycle of flash memory due to the limited number of writes before erasures, leading to unnecessary data erasure and reduced storage capacity.
Innovation Solution
The implementation of modified one-hot (MOH) codes and write-once memory (WOM) codes that minimize the number of memory cells encoded for each write operation, allowing for re-use of written cells and achieving high sum-rates with balanced wear, thereby extending the life of flash memory devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional flash memory programming methods are used to increase cell voltage levels, then data can be stored, but the number of rewrite operations is limited to 10,000-100,000 erasures before the memory lifecycle ends
Solution Approach 1:
The patent changes the parameter representation from traditional binary (0-1) to quaternary (0-3) cell levels, enabling four distinct states per cell. This parameter expansion allows encoding more information per cell and supports the WOM code structure that tracks write generations, thereby increasing the number of usable writes before erasure while maintaining reliability
Solution Approach 2:
The patent segments the memory block into multiple generations of writes, where each generation uses a subset of cells. By dividing the write operations into generations and using combinatorial coding to select which cells to write in each generation, the system can perform many more writes than traditional methods without requiring full block erasure, thus extending the memory lifecycle
2Ease of operation
If a block of cells is used for programming, then electron injection can increase voltage levels, but all cells in the block must be erased together even if only one cell needs deletion
Solution Approach 1:
The patent divides the block into generations, where each generation uses a specific subset of cells. This segmentation allows individual cells or small groups to be targeted for writing without affecting the entire block. The combinatorial coding scheme enables selective cell usage across generations, providing fine-grained control that prevents unnecessary erasure of other cells when only specific data needs to be modified
Solution Approach 2:
The patent implements dynamic cell allocation where the set of active cells changes with each generation. Instead of static block-wide operations, the system dynamically selects which cells to program based on the current generation and data requirements. This dynamic approach enables precise targeting of only the necessary cells for each write operation, avoiding unnecessary erasures
3Productivity
If multiple level cells (MLC) with four levels or triple level cell (TLC) with eight levels are used to increase cell sum-rate, then storage capacity increases, but error correction and interference become more difficult to manage
Solution Approach 1:
The patent uses quaternary cells (four levels) as a balanced choice that provides high sum-rate while maintaining manageable error characteristics. The WOM code structure with generation tracking and combinatorial coding is specifically designed to work with these parameter levels, providing built-in error handling through the structured approach to cell selection and voltage level management, reducing interference issues compared to higher-level cells
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
These codes achieve the highest sum-rates possible while reducing the trade-offs between high sum-rate and high writes, allowing for a large number of writes before erasures, ensuring even wear of cells, and extending the lifespan of flash memory devices without the need for extra storage units.
Implementation Method 1
Programming a memory cell (hereinafter referred to as a 'cell') is done by electron injection (i.e., hot electron injection creates an electric field) to increase the voltage incrementally above a charge threshold
Implementation Method 2
Programming a memory cell (hereinafter referred to as a 'cell') is done by electron injection (i.e., hot electron injection creates an electric field) to increase the voltage incrementally above a charge threshold
Data Source
AI summary
Provided are modified one-hot (MOH) constructions for WOM codes with low encoding and decoding complexity, that achieve high sum-rates. Features include maximizing writing of data information values for successive rewrites, all-zero and all-one cell state vectors that represent a unique data information value that can be written for many generations, a very high number of writes, and does not sacrifice capacity. One embodiment comprises ordered or unordered MOH code that approaches the upper-bound for large n wits. According to the embodiments, before an erasure is needed, the majority of the wits are encoded, which provides level wearing and maximizes life of cells.