Memory Device Weak Cell Refresh Control
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Solution Overview
Problem
Memory devices face data retention issues due to leakage currents in weak memory cells, leading to errors when their retention time is shorter than the majority, causing stored data to degrade prematurely.
Innovation Solution
A memory device is designed with a peripheral circuit capable of performing additional refresh operations for weak memory cells, utilizing a nonvolatile memory unit to store weak row addresses and a refresh control unit to manage these operations, ensuring data retention by performing second refresh operations at specific intervals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a standard refresh operation is performed at regular intervals for all memory cells, then data retention for the majority of memory cells is maintained, but weak memory cells with shorter retention times experience data loss
Solution Approach 1:
The patent segments the memory cell population into two categories: normal memory cells and weak memory cells. This segmentation allows different refresh strategies to be applied to each group, with standard refresh operations for normal cells and additional accelerated refresh operations for weak cells, thereby resolving the contradiction between maintaining data retention for all cells while accommodating the specific needs of weak cells
Solution Approach 2:
The patent applies local quality by implementing location-specific refresh operations. Weak memory cells are identified and targeted with additional refresh operations at specific time points within the refresh cycle. This localized approach ensures that weak cells receive the extra attention they need without subjecting all memory cells to unnecessary operations, thus maintaining reliability for all cells while adapting to the specific weaknesses of certain cells
2Reliability
If additional refresh operations are performed for weak memory cells, then data retention for weak memory cells is improved, but the device complexity increases
Solution Approach 1:
The patent implements preliminary action by pre-characterizing memory cells during a training phase to identify weak cells before normal operation begins. The locations of weak memory cells are stored in a separate memory structure during this initial phase. During normal operation, this pre-acquired information is used to automatically trigger additional refresh operations for identified weak cells, eliminating the need for complex real-time analysis and simplifying the operational refresh control mechanism
Solution Approach 2:
The patent enables self-service by allowing the memory device to automatically manage its own weak cell refresh requirements. The system uses internally stored information about weak cell locations to autonomously determine when and where to perform additional refresh operations without requiring external control or complex decision-making logic, thereby improving reliability for weak cells while keeping the control mechanism relatively simple
Data Source
AI summary
A memory device may include a plurality of word lines each word line being operably coupled to one or more memory cells; a peripheral circuit suitable for performing first and second refresh operations to the plurality of word lines; wherein the first refresh operation is suitable for preserving stored data for a majority of the memory cells of the memory device and the second refresh operation is suitable for preserving stored data of one or more weak memory cells.