NAND Flash Controller Wear-Adaptive Read Method
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Solution Overview
Problem
In non-volatile memory systems like NAND-type flash memory, the reliability of read operations deteriorates over time due to insulating film degradation from repeated data writing and erasing, making it challenging to maintain performance and reliability without unnecessary increases in read time or decreases in reliability.
Innovation Solution
A memory system with a controller that selects an appropriate read method based on the wear state of memory cells by executing an examination read command after writing operations, using stress metrics like program disturb, data retention, and temperature crossover to determine the optimal read method for each block, thereby maintaining reliability while minimizing performance loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple write and erase operations are performed on memory cells, then data storage capacity is improved, but insulating film deterioration occurs and read operation reliability decreases
Solution Approach 1:
The patent applies preliminary action by performing examination read operations at predetermined intervals after write operations to detect insulating film deterioration before it significantly impacts read reliability. This proactive detection allows the system to identify wear state changes early and adjust read methods accordingly, preventing reliability degradation while maintaining data storage capacity through multiple P/E cycles
2Reliability
If a conservative read method is selected to maintain reliability, then read operation reliability is preserved, but read time increases and performance decreases
Solution Approach 1:
The patent implements dynamics by dynamically selecting read methods based on the detected wear state of memory blocks. The controller monitors examination read results and adjusts the read method in real-time: using fast read methods for blocks in good condition and conservative read methods only when wear is detected. This dynamic adaptation resolves the contradiction by matching read methodology to actual block health status rather than applying a static conservative approach to all blocks
Solution Approach 2:
The patent applies local quality by treating different memory blocks differently based on their individual wear states. Instead of applying a uniform read method across all blocks, the system identifies specific blocks exhibiting wear characteristics through examination reads and applies targeted read methods only to those blocks. This localized approach ensures reliability is maintained only where necessary while preserving fast read performance for healthy blocks
3Measurement precision
If frequent examination read commands are executed to monitor wear state, then wear detection accuracy is improved, but system performance and productivity decrease
Solution Approach 1:
The patent applies periodic action by executing examination read commands at predetermined intervals rather than continuously or after every write operation. This periodic monitoring strategy detects wear state changes effectively while minimizing the performance impact of examination operations. The interval-based approach balances wear detection accuracy with system productivity by performing examinations only when necessary to track wear progression
Data Source
AI summary
According to one embodiment, there is provided a memory system including a non-volatile memory, and a controller. The controller selects one read method from a plurality of read methods with different time required to perform a read operation on the non-volatile memory and issues a first read command according to the selected one read method to the non-volatile memory.