NAND Flash Plane Selection for Reserved Block Storage
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Solution Overview
Problem
Manufacturing yield loss in NAND Flash memory devices occurs due to the exclusion of defective dies with fewer valid blocks, as the existing method of storing read-only and backup reserved blocks reduces the number of valid blocks below the minimum threshold, leading to non-defective dies being deemed defective.
Innovation Solution
Selecting planes to store read-only and backup reserved blocks based on the number of valid blocks in each plane during the manufacturing process, using fuse bit circuitry to identify optimal locations, thereby reducing the number of valid blocks required for each plane and preventing yield loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If read-only and backup reserved blocks are stored in fixed plane locations, then the placement method is simple, but the number of valid blocks in each plane is reduced below the minimum threshold, causing non-defective dies to be deemed defective
Solution Approach 1:
The patent applies local quality by assigning different functions to different planes based on their specific characteristics. Instead of uniformly storing reserved blocks in fixed locations across all dies, the system identifies planes with sufficient valid block capacity and stores reserved blocks only in those specific planes. This localized approach ensures that the reserved block storage does not reduce the valid block count below the minimum threshold in any plane, thereby maintaining accurate die classification while preserving manufacturing simplicity.
2Reliability
If the minimum Number of Valid Blocks (NVB) threshold is strictly enforced, then defective dies are reliably identified, but non-defective dies with fewer blocks are mistakenly rejected, reducing manufacturing yield
Solution Approach 1:
The patent changes the parameter of reserved block placement from fixed locations to dynamic locations selected based on plane characteristics. By evaluating the number of valid blocks in each plane and selecting planes that can accommodate reserved blocks without falling below the minimum NVB threshold, the system maintains the reliability of defective die identification while increasing manufacturing yield. This parameter change allows non-defective dies with fewer total blocks to be correctly classified and produced.
3Productivity
If reserved blocks are placed in planes with higher valid block counts, then manufacturing yield is improved, but the system complexity increases due to plane evaluation and selection
Solution Approach 1:
The patent applies preliminary action by evaluating and selecting appropriate planes for reserved block storage during the manufacturing process before final die classification. By pre-identifying planes with sufficient valid block capacity and marking them for reserved block storage, the system improves manufacturing yield without significantly increasing overall complexity. The plane selection is performed once during initialization, and subsequent operations simply reference the pre-determined plane assignments.
Data Source
AI summary
Manufacturing yield loss of NAND Flash dies is reduced by selecting a plane to store a read-only reserved block and another plane to store a backup read-only reserved block based on the Number of Valid Blocks (NVB) blocks in each plane in the NAND Flash array.