3D NAND Read Setup via Dual Queue Management
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
3D NAND flash memory experiences voltage threshold deviations over time, leading to unintended changes in logical states of cells, which error correcting codes can only partially correct, necessitating a method to prevent such deviations.
Innovation Solution
Implementing a read setup operation that utilizes a first-in first-out (FIFO) queue and a least recently used (LRU) queue to identify and perform read setup operations on blocks that have been accessed for a predetermined threshold time, thereby reducing voltage threshold deviations by maintaining the memory cells in a conditioned state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If read setup operation is performed on all accessed blocks, then voltage threshold deviation is reduced, but device complexity and operational overhead increase
Solution Approach 1:
The patent divides the memory block management into two separate queues: a first queue for recently accessed blocks and a second queue for blocks needing read setup. This segmentation allows the system to track different block states independently, reducing the complexity of managing all blocks uniformly while ensuring that only appropriate blocks undergo read setup operations.
Solution Approach 2:
The patent performs read setup operations in advance on blocks identified in the second queue before they are actually read. By proactively preparing blocks that have been accessed a threshold amount of time ago, the system prevents voltage threshold deviation before it occurs, rather than reacting after the problem manifests.
2Reliability
If read setup operation is performed frequently, then voltage threshold deviation is reduced, but energy consumption increases
Solution Approach 1:
The patent applies read setup operations selectively rather than universally. By using the two-queue system to identify only those blocks that have been accessed for a predetermined threshold time, the patent performs partial read setup actions on a subset of blocks, avoiding unnecessary energy consumption on blocks that don't require it while still maintaining data integrity for at-risk blocks.
Solution Approach 2:
The patent implements periodic monitoring of block access patterns through the queue system. Blocks are evaluated at threshold intervals to determine if they need read setup, creating a periodic rather than continuous operation that reduces energy consumption while maintaining reliability.
3Measurement precision
If blocks are tracked in detailed queues, then read setup timing is optimized, but loss of time for queue management increases
Solution Approach 1:
By segmenting blocks into two distinct queues based on their access patterns and timing requirements, the patent enables more precise tracking of blocks that need read setup. The first queue captures recent accesses with high timing precision, while the second queue identifies blocks approaching the threshold, allowing optimized read setup scheduling without managing all blocks uniformly.
Data Source
AI summary
A method of operating a memory is provided. The method includes, in response to an access of a block of memory updating a first queue to identify the accessed block in response to a determination that the block is not already identified in the first queue and a determination that the block is not already identified in a second queue, and updating the second queue to identify the accessed block of memory in response to a determination that the block is already identified in the first queue. The method further includes scanning the second queue to identify, as a read setup candidate, each block of the memory that is identified as present in the second queue longer than a threshold, and performing a read setup operation on a block of memory that has been identified as the read setup candidate.