NAND Memory Defect Repair Using Weight-Based Column Selection

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

NAND flash devices face inefficiencies in defect repair due to limited redundant columns, requiring a method to selectively disable and replace defective data columns with optimal computation efficiency and repair performance.

Innovation Solution

A weight-based column repair algorithm that calculates a 'weight of block' ratio to prioritize defective blocks for repair, based on the number of affected blocks and defective columns, ensuring maximum repair coverage with available redundant columns.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a limited number of redundant columns are used to replace defective data columns, then the device can maintain operation with some defects, but the number of defe ective blocks that can be repaired is limited

Engineering Contradiction:

Improvedevice operation with defectsVSAvoidnumber of defective blocks repaired

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent changes the selection parameter from simple defect count to a weight-based metric that considers both the number of defective columns in a block and the number of blocks affected by those defective columns. This parameter transformation enables optimized selection of which defective blocks to repair first, maximizing the utilization of limited redundant columns.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies different weights to different defective blocks based on their local characteristics (number of defective columns and affected blocks). Instead of treating all defective blocks uniformly, the system identifies and prioritizes blocks with higher weights, thereby locally optimizing the repair process to achieve global improvement in repair efficiency.

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If defective blocks are selected for repair without optimization, then the repair process is simple, but computation efficiency and repair performance deteriorate

Engineering Contradiction:

Improverepair process simplicityVSAvoidcomputation efficiency and repair performance

Core Design Contradiction:

Ease of manufactureVSProductivity

Solution Approach 1:

The patent performs preliminary calculation of weight values for all defective blocks before the actual repair process. By pre-computing the weight metric that considers both defective column count and affected block count, the system prepares an optimized repair sequence in advance, ensuring that when repair begins, the selection process is efficient and performance is maximized.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9558852B2Method and apparatus for defect repair in NAND memory device

Publication Date: 2017.01.31 ADVANTEST CORP

AI summary

System and method of selecting defective columns in NAND memory devices for repair. After locating the defective blocks and defective columns in a NAND memory device, a weight value is calculated for each defective block by dividing a total number of defective blocks that would be inherently repaired as a result of repairing the respective defective block by a number of defective data columns in the respective defective block. A defective block with the greatest weight value is selected for repair in which the defective columns in the selected block are substituted by redundant columns. Other defective blocks with defective columns having the same column addresses with the defective columns in the selected defective block are automatically selected for repair as well. Remaining defective columns are selected for repair by iteratively updating weight values and selecting a defective block that has the greatest weight value among the remaining defective blocks.