Semiconductor Memory Block Defect Isolation via Fuse Circuit
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Solution Overview
Problem
As semiconductor memory devices integrate more memory cells per area, the yield decreases, and failed cells within memory blocks are often unrecoverable, leading to rejected devices due to the inefficiency of existing repair methods, particularly the row redundancy scheme, which consumes excessive resources and is uneconomical.
Innovation Solution
A semiconductor memory device design that includes a cell array divided into blocks, with a nonvolatile storage circuit to store address information of defective blocks and a fuse circuit to inhibit activation of word lines in defective blocks, allowing for external management and access avoidance, thereby improving reliability and reducing resource consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of memory cells integrated in a same area is increased, then the integration and performance are improved, but the yield is relatively decreased
Solution Approach 1:
The cell array is divided into multiple blocks, and each block is independently managed. When defects are detected in a specific block, only that block is marked as defective and excluded from operation, while the remaining blocks continue to function normally. This segmentation allows the device to maintain higher yield by salvaging functional blocks even when some blocks contain defects.
2Measurement precision
If failed cells are detected by a memory block unit, then the defective blocks can be identified, but the failed cells are typically not easily repaired and the DRAM including the failed cells is often rejected
Solution Approach 1:
The defective block is extracted from the functional memory system by marking its address in the nonvolatile storage circuit. The fuse circuit then cuts off the word lines corresponding to the defective block, effectively removing it from operation. This extraction approach allows the rest of the memory device to continue functioning at full capacity, transforming a previously rejectable device into a usable one.
Solution Approach 2:
The invention changes the operational state of defective blocks by modifying the electrical parameters of their word lines through the fuse circuit. By cutting off the word lines, the device transitions the defective block from an active state to an inactive state, preventing further operation of faulty cells while preserving the functionality of healthy blocks.
3Ease of repair
If row redundancy scheme is used to repair failed cells, then some defects can be corrected, but it consumes excessive resources and is uneconomical
Solution Approach 1:
Instead of implementing complex and resource-intensive row redundancy schemes, the invention uses a simpler approach: marking defective block addresses in a nonvolatile storage circuit and cutting off word lines with fuse circuits. This disposable approach to defective blocks (simply excluding them rather than repairing them) consumes fewer resources while achieving the practical goal of maintaining device functionality.
Data Source
AI summary
A semiconductor memory device may include a cell array comprising a plurality of memory cells, each memory cell connected to a word line and a bit line, the cell array divided into a plurality of blocks, each block including a plurality of word lines, the plurality of blocks including at least a first defective block; a nonvolatile storage circuit configured to store address information of the first defective block, and to output the address information to an external device; and a fuse circuit configured to cut off an activation of word lines of the first defective block.