Flash Memory Read Reclaim for Hot-Spot Word Lines
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Solution Overview
Problem
Flash memory cells experience threshold voltage shifts due to read disturbances, leading to read failures and increased write operations, which are exacerbated by high-voltage read pass voltages applied to unselected word lines.
Innovation Solution
A storage device with a memory controller that selectively performs block or word line reclaim operations based on the deterioration level of adjacent word lines, using a higher pass voltage on unselected lines to mitigate read disturbances and reduce the number of write operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high-voltage read pass voltage is applied to unselected word lines during read operation, then read operation can be performed, but threshold voltage of memory cells increases leading to read failure
Solution Approach 1:
The patent performs a reclaim operation on the adjacent word line before the read disturbance causes threshold voltage shift and read failure. By proactively detecting deterioration and performing reclaim (moving valid data to new locations and erasing the deteriorated word line), the system prevents read failures before they occur, while still allowing normal read operations to proceed at high speed.
2Reliability
If block reclaim operation is performed to recover from read disturbance, then read reliability is improved, but number of write operations increases
Solution Approach 1:
The patent segments the reclaim operation from the block level to the word line level. Instead of performing a full block reclaim operation that would affect all word lines in a block, the system performs reclaim only on the specific adjacent word line that has deteriorated. This segmentation reduces the scope of the reclaim operation, thereby reducing the number of write operations required while still maintaining read reliability for the affected word line.
3Productivity
If word line reclaim operation is performed on adjacent word line, then read disturbance is reduced and write operations are minimized, but device complexity increases
Solution Approach 1:
The patent applies local quality by targeting the reclaim operation specifically to the adjacent word line that has deteriorated, rather than applying uniform reclaim operations across the entire block. The memory controller monitors deterioration levels of adjacent word lines and performs reclaim only where needed, creating a localized solution that reduces overall system complexity compared to blanket block-level reclaim operations.
Data Source
AI summary
A storage device including: a flash memory including a selected word line and an adjacent word line adjacent to the selected word line; and a memory controller configured to provide a select read voltage to the selected word line and a pass voltage to the adjacent word line during a read operation, the pass voltage being higher than the select read voltage, and wherein the memory controller is further configured to determine whether the selected word line is a hot spot read word line based on a deterioration level of the adjacent word line, and perform a word line reclaim operation for the adjacent word line when the selected word line is the hot spot read word line.