Obsolete Block Charge Management for Flash Memory Retention
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Solution Overview
Problem
In flash memory systems, blocks containing obsolete data can negatively affect data retention in neighboring blocks, particularly in multi-level cell (MLC) blocks, due to differences in charge density, leading to inefficient erase operations and reduced memory endurance.
Innovation Solution
Identifying blocks with obsolete data and charging their memory cells to elevated charge levels, which neutralizes the impact on neighboring blocks without verifying specific memory states, allowing for rapid charging and maintaining these levels until new data is written, thereby eliminating the tendency of obsolete blocks to affect data retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If blocks containing obsolete data are maintained in their original charge levels, then the memory system can retain data without frequent erase operations, but the obsolete blocks negatively affect data retention in neighboring MLC blocks due to charge density differences
Solution Approach 1:
The patent applies preliminary anti-action by proactively charging obsolete blocks to elevated charge levels before they can negatively impact neighboring MLC blocks. This preventive measure neutralizes the harmful charge density differential that would otherwise cause data retention issues in adjacent blocks, allowing the system to maintain both long data retention and high reliability simultaneously.
2Reliability
If erase operations are performed frequently on blocks with obsolete data to maintain data retention, then reliability is improved, but the memory endurance is reduced due to increased erase cycles
Solution Approach 1:
The patent implements preliminary action by charging obsolete blocks to elevated charge levels in advance, which eliminates the need for frequent erase operations. This preliminary charging action prevents the formation of harmful charge density differentials, thereby maintaining data retention reliability without subjecting the memory to excessive erase cycles that would reduce overall endurance.
3Manufacturing precision
If conventional programming verification is performed on blocks being charged to elevated charge levels, then programming precision is maintained, but the charging process becomes time-consuming and reduces productivity
Solution Approach 1:
The patent applies partial action by charging obsolete blocks to elevated charge levels that exceed the threshold required for valid data storage. Since these blocks contain only obsolete data, the excess charge beyond what would be needed for normal programming does not affect system functionality, allowing rapid charging without verification and thereby significantly improving productivity while maintaining sufficient programming precision for the intended purpose.
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
This approach improves data retention by stabilizing charge density in obsolete blocks, reducing the frequency of erase operations, and extending the memory's endurance by minimizing the disturbance on adjacent MLC blocks, thus enhancing overall memory performance and reliability.
Implementation Method 1
charging the floating gates of the erase block from the programmed charge levels to elevated charge levels
Data Source
AI summary
In a nonvolatile memory array, blocks that contain only obsolete data are modified by adding charge to their cells, increasing the charge level from the programmed charge levels that represented obsolete data to elevated charge levels. The increase in overall charge in such blocks lessens the tendency of such blocks to impact data retention in neighboring blocks.