NAND Flash Controller Wear Distribution via Block Disassembly
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Solution Overview
Problem
In NAND flash memory systems, wear in tunnel oxide films due to repetitive programming and erasing operations leads to failed operations, resulting in unusable blocks and reduced storage capacity and performance over time.
Innovation Solution
A memory system with a controller circuit that manages logical blocks by monitoring erasing and programming time lengths of physical blocks, disassembling logical blocks when blocks with different wear levels are mixed, and reassembling them with blocks of similar wear characteristics to distribute wear evenly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If erase operations are performed on physical blocks in NAND flash memory, then storage capacity is utilized, but wear in tunnel oxide films increases leading to failed operations and reduced lifespan
Solution Approach 1:
The patent applies local quality by monitoring and identifying physical blocks with different wear levels (good blocks with shorter erase times vs. worn blocks with longer erase times) and treating them differently through selective disassembly and reassembly operations, rather than uniformly treating all blocks
Solution Approach 2:
The patent performs preliminary action by monitoring erase time lengths before blocks fail, identifying worn blocks in advance, and proactively disassembling logical blocks containing mixed wear-level blocks before actual failures occur, thereby preventing future operation failures
2Ease of operation
If physical blocks with different wear levels are grouped in the same logical block, then erase operations can be performed, but wear distribution becomes uneven leading to premature failure of the logical block
Solution Approach 1:
The patent segments logical blocks into smaller units and reassembles them based on wear characteristics, separating blocks with different wear levels into different logical blocks to ensure uniform wear distribution and extend overall system lifespan
Solution Approach 2:
The patent changes the composition parameter of logical blocks by dynamically selecting which physical blocks to group together based on their wear levels (erase time lengths), creating logical blocks with homogeneous wear characteristics to optimize performance and lifespan
3Reliability
If worn physical blocks are treated as bad blocks, then failed operations are prevented, but total physical capacity is reduced and SSD lifespan is shortened
Solution Approach 1:
The patent recovers worn physical blocks by disassembling logical blocks containing mixed wear-level blocks and reassembling them into new logical blocks with uniform wear characteristics, thereby recovering capacity that would otherwise be lost and extending SSD lifespan
Data Source
AI summary
Aspects of the present disclosure include a memory system monitors at least one of an erasing time length and a programming time length of each of physical blocks included in a first logical block among a plurality of logical blocks. The memory system disassembles the first logical block among the plurality of logical blocks when both of a first physical block and a second physical block exist in the first logical block, the first physical block having an erasing time length or a programming time length falling within a first range, and the second physical block having an erasing time length or a programming time length falling outside the first range.