Flash Memory Data Retention via Rewrite Refresh
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Solution Overview
Problem
Flash memory devices experience data retention decay over time, leading to loss of stored data, particularly in applications requiring long-term data integrity, as conventional refresh mechanisms degrade storage capacity and integrity.
Innovation Solution
Implementing a reprogram operation to refresh memory cells by resetting their charge or voltage levels to default states without erasing, thereby extending data retention and reducing the need for full program/erase cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional refresh mechanisms are used to maintain data retention, then data retention is improved, but storage capacity and integrity are degraded
Solution Approach 1:
The flash memory array is divided into multiple blocks, and the refresh operation is applied selectively to individual blocks or pages rather than the entire array. This segmentation allows targeted refreshing of only the affected areas, preserving the integrity and capacity of the rest of the storage space while maintaining data retention in the refreshed sections.
Solution Approach 2:
The invention changes the parameter of charge level within memory cells by applying a rewrite refresh operation that modifies charge levels without requiring full erase and program cycles. This parameter change approach allows data retention maintenance while avoiding the detrimental effects of conventional refresh mechanisms on storage capacity and integrity.
2Reliability
If full program/erase cycles are performed for refresh, then data retention is maintained, but memory cell endurance is reduced
Solution Approach 1:
Instead of performing complete program/erase cycles for refresh, the invention applies a partial rewrite operation that only modifies the charge levels of affected memory cells. This partial action approach maintains data retention while significantly reducing the wear and tear on memory cells, thereby extending their operational lifespan and endurance.
Solution Approach 2:
The invention extracts the essential function of refresh (maintaining charge levels) while removing the harmful components of conventional refresh (full erase and program cycles). By taking out only the necessary charge level adjustment and eliminating the damaging full cycle operation, the system achieves data retention maintenance without compromising memory cell endurance.
3Reliability
If frequent refresh operations are performed, then data retention is improved, but device complexity and operational overhead increase
Solution Approach 1:
The flash memory system performs self-refresh operations automatically based on detected conditions such as charge level degradation or time elapsed since last refresh. This self-service mechanism eliminates the need for complex external refresh management systems, reducing device complexity while maintaining effective data retention through automated, condition-based refresh operations.
Data Source
AI summary
Providing for extended data retention of flash memory devices by program state rewrite is disclosed herein. By way of example, a memory cell or group of memory cells can be evaluated to determine a program state of the cell(s). If the cell(s) is in a program state, as opposed to a natural or non-programmed state, a charge level, voltage level and/or the like can be rewritten to a default level associated with the program state, without erasing the cell(s) first. Accordingly, conventional mechanisms for refreshing cell program state that require rewriting and erasing, typically degrading storage capacity of the memory cell, can be avoided. As a result, data stored in flash memory can be refreshed in a manner that mitigates loss of memory integrity, providing substantial benefits over conventional mechanisms that can degrade memory integrity at a relatively high rate.