Temperature-Informed Memory Refresh for NAND Flash
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Solution Overview
Problem
Memory devices, particularly NAND flash devices, experience increased raw bit error rates and performance issues due to temperature variations between write and read operations, leading to cross-temperature problems that require costly error handling and resource-intensive refresh processes.
Innovation Solution
Implementing extreme write temperature counters at a superblock level to identify refresh candidates and perform temperature-informed memory refreshes, which reduces error-handling events and minimizes resource usage by refreshing data only when ambient temperatures are acceptable, thereby preserving data integrity and reducing wear on memory cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If error handling is performed to address cross-temperature RBER events, then data integrity is maintained, but read latency increases and performance deteriorates
Solution Approach 1:
The patent performs preliminary refresh operations on memory blocks that were written at extreme temperatures before normal read operations. By proactively refreshing data at extreme write temperatures (detected via temperature counters) during background operations or low-activity periods, the system prevents cross-temperature errors from occurring in the first place, eliminating the need for error handling during critical read operations and thus avoiding read latency penalties.
2Reliability
If frequent refresh operations are performed to prevent cross-temperature errors, then data reliability improves, but device wear increases and resources are consumed
Solution Approach 1:
The patent applies refresh operations selectively only to memory blocks that were written at extreme temperatures, identified by temperature counters associated with specific blocks. Instead of uniformly refreshing all memory blocks, the system targets only those blocks with temperature counters indicating extreme write conditions, thereby reducing unnecessary refresh operations and minimizing wear on memory cells that do not require refreshing.
Solution Approach 2:
The patent uses temperature counters as a parameter to identify blocks requiring refresh. By monitoring and comparing temperature counter values against thresholds, the system dynamically determines which blocks need refreshing based on their write temperature history, enabling selective refresh operations that improve reliability only where necessary while conserving device resources and extending lifespan.
3Reliability
If temperature monitoring and selective refresh are implemented, then cross-temperature errors are reduced, but device complexity and processing overhead increase
Solution Approach 1:
The patent implements a self-service mechanism where the memory device autonomously monitors its own temperature conditions and performs selective refresh operations without requiring external controller intervention. Temperature counters are maintained within the device, and refresh decisions are made automatically based on counter values, reducing the processing burden on external controllers and minimizing additional overhead while maintaining error reduction capabilities.
Data Source
AI summary
Devices and techniques for temperature informed memory refresh are described herein. A temperature counter can be updated in response to a memory device write performed under an extreme temperature. Here, the write is performed on a memory device element in the memory device. The memory device element can be sorted above other memory device elements in the memory device based on the temperature counter. Once sorted to the top of these memory device elements, a refresh can be performed the memory device element.