Data Shaping for Flash Memory Error Rate Reduction
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Solution Overview
Problem
Flash memory devices experience errors due to non-optimal read voltage distributions, leading to unusable cells and reduced capacity and lifespan, as defects cause voltage ranges to shift or overlap, making it difficult to distinguish between states and resulting in read errors.
Innovation Solution
Implementing data shaping techniques to modify the distribution of data within cells based on detected or expected voltage distributions, reducing the likelihood of writing data to error-prone states and increasing the probability of writing to non-error-prone states, thereby reducing error rates and extending the device's lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple bits are stored in each flash memory cell to increase storage density, then storage capacity is improved, but error rates increase due to voltage distribution shifts and overlaps
Solution Approach 1:
The system performs preliminary characterization of voltage distributions for each memory block before data writing. By detecting voltage distribution parameters (mean, standard deviation) in advance and determining error-prone states beforehand, the system can pre-calculate shaping parameters that will prevent data from being written to error-prone states, thus resolving the contradiction between high-density storage and reliability
Solution Approach 2:
The system changes the data distribution parameters by applying data shaping that modifies the probability of writing to different states. By adjusting the data distribution to avoid error-prone states (changing the statistical parameters of data placement), the system maintains high storage utilization while reducing error rates in multi-bit flash memory cells
2Productivity
If data is written to all available states in memory cells, then storage utilization is improved, but error rates increase due to writing to error-prone states
Solution Approach 1:
The system applies different data shaping parameters to different blocks of memory based on their individual voltage distribution characteristics. Each block is characterized locally to identify its specific error-prone states, and data shaping is customized for each block to maximize utilization while avoiding local error-prone conditions, thus resolving the contradiction between storage utilization and reliability
3Measurement precision
If read voltage thresholds are established to distinctly divide cell states, then reading accuracy is improved, but defects cause voltage distributions to shift or expand making differentiation difficult
Solution Approach 1:
The system performs preliminary detection of voltage distribution parameters for each memory block before data operations. By characterizing the voltage distributions (mean, standard deviation) in advance, the system can identify error-prone states and adjust data shaping parameters to avoid these states, thereby maintaining reading accuracy despite voltage shifts and expansions caused by defects
Data Source
AI summary
Systems and methods are described for reducing error rates on data storage devices by applying data shaping to data written to such devices in order to avoid error-prone states on cells within the devices. Different states of individual cells (such as those representing different bit patterns) may have different propensities for error, and these propensities may vary during operation of a device. Thus, a device as disclosed herein may determine error-prone states for a cell or group of cells, and apply data shaping to data written to such cells to reduce the likelihood that writing the data places the cell or cells into an error-prone state. Data shaping may be used, for example, to increase the occurrence of “0” bits within input data, thus avoiding error-prone low voltage states that may be used to represent a series of “1” bits.