NAND Memory Partial Bad Block Remapping
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Solution Overview
Problem
In NAND memory systems, identifying and avoiding entire bad blocks reduces memory capacity, and insufficient spare blocks can lead to inability to replace bad blocks, highlighting the need for a method to utilize partial bad blocks effectively.
Innovation Solution
Dynamic remapping of partial bad blocks, where unusable wordlines in NAND memory are identified and replaced with spare blocks, allowing partial bad blocks to be used without discarding the entire block, thereby increasing logical capacity and avoiding unnecessary reduction in memory usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If entire bad blocks are avoided or replaced, then data reliability is improved, but memory capacity is reduced
Solution Approach 1:
The patent segments the memory block into individually addressable wordlines, allowing selective identification and remapping of only the defective wordlines rather than treating the entire block as defective. This enables partial blocks with some good wordlines to be reused, thereby maintaining memory capacity while ensuring data reliability through selective avoidance of bad wordlines.
Solution Approach 2:
The patent applies local quality by treating each wordline within a block independently, assigning different quality statuses (good or bad) to different wordlines rather than uniformly treating the entire block. This allows the system to utilize portions of blocks that have local defects, optimizing the balance between reliability and capacity by using only the good portions of each block.
2Device complexity
If insufficient spare blocks are available, then device complexity is reduced, but the ability to replace bad blocks is compromised
Solution Approach 1:
The patent segments the replacement strategy into wordline-level operations rather than block-level operations. By identifying and remapping individual bad wordlines to good wordlines within the same or different blocks, the system eliminates the need for entire spare blocks, thereby reducing device complexity while maintaining the ability to replace defective portions.
Solution Approach 2:
The patent recovers usable capacity from blocks that would traditionally be discarded as completely bad. By identifying good wordlines within blocks containing bad wordlines and remapping them for use, the system recovers partial block capacity, reducing the need for spare blocks while maintaining replacement capability for defective portions.
Data Source
AI summary
A system handles bad blocks in block-based NAND memory by remapping wordlines that are unusable. Rather than eliminate usage of an entire block, the system may dynamically remap the block to exclude only the unusable wordlines. The partial blocks utilize portions of the memory with good wordlines and the portions of memory with bad wordlines are redirected to one or more replacement blocks.