Flash Memory Erase Depth Control via Cell Grouping
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Solution Overview
Problem
As storage density increases in data storage devices like flash memory, variations in erase speed and duration among cells become more pronounced due to factors such as cell damage, charge leakage, and manufacturing differences, leading to inconsistent data retrieval and storage reliability.
Innovation Solution
Implementing an erase depth control system that uses different voltage profiles for different sets of storage cells within a block, determining the erase speed and duration based on verify voltage thresholds to ensure consistent and efficient erasure, thereby compensating for variations in cell performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single erase operation is applied to all storage cells in a block, then the erase operation is simple and fast, but cells with different erase speeds result in inconsistent erasure and reduced reliability
Solution Approach 1:
The patent divides storage cells into multiple groups based on their erase speeds. A controller performs separate erase operations on different groups of cells, where each group is identified by its erase speed characteristics. This segmentation allows tailored erase parameters for each group, ensuring consistent erasure across all cells while managing complexity through systematic organization.
Solution Approach 2:
The patent applies different erase parameters to different groups of storage cells based on their individual erase speed characteristics. Instead of uniform treatment, each group receives customized voltage profiles and timing parameters appropriate to its erase speed, thereby achieving locally optimized erasure quality that contributes to overall reliability.
2Reliability
If different voltage profiles are applied to different sets of cells to match erase speeds, then erase consistency and reliability improve, but the complexity of controlling and managing multiple voltage profiles increases
Solution Approach 1:
The patent implements dynamic voltage control where the controller adapts voltage profiles based on real-time or pre-characterized erase speed data of different cell groups. The system dynamically selects and applies appropriate voltage parameters for each group during erase operations, enabling reliable erasure while managing control complexity through automated adaptation rather than static fixed parameters.
Solution Approach 2:
The patent employs feedback mechanisms where the controller monitors erase progress or uses pre-stored erase speed characteristics to determine appropriate voltage profiles for different cell groups. This feedback loop enables the system to adjust voltage parameters based on actual or historical performance data, ensuring data integrity while automating the control process to manage complexity.
3Reliability
If erase speed variations among cells are ignored, then the control process remains simple, but cell degradation increases and storage reliability decreases
Solution Approach 1:
The patent performs preliminary characterization or identification of cell groups based on their erase speeds before the main erase operation. This preliminary sorting or grouping allows the controller to prepare and apply optimized voltage profiles in advance for each group, preventing unnecessary cell degradation from mismatched parameters while streamlining the overall erase process to minimize time loss.
Data Source
AI summary
Apparatuses, systems, methods, and computer program products are disclosed for erase depth control. One apparatus includes a block of non-volatile storage cells. A controller is configured to perform a first erase operation on a block of non-volatile storage cells. A controller for a block is configured to determine a first set of storage cells of the block having a faster erase speed than a second set of storage cells of the block based on a verify voltage threshold. A controller for a block is configured to perform a second erase operation on the block using different voltages for a first set of storage cells and a second set of storage cells of the block.