Word Line Defect Detection in Non-Volatile Memory
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Solution Overview
Problem
Existing non-volatile semiconductor memory technologies, such as EEPROM and flash memory, face challenges in detecting defects in word lines, particularly 'broken' word lines with abnormally high resistance, which can lead to under-programmed storage elements that are not detected during programming, causing errors.
Innovation Solution
The implementation of a method that involves programming storage elements to multiple states, using threshold voltage distributions to identify under-programmed cells by performing reads at specific reference voltages after programming, and maintaining information on intended states to accurately assess word line defects without additional data latches, allowing for the detection of broken word lines and other defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If word line resistance is slightly elevated but not extremely high, then the defect may not be detected during programming, but it can still cause under-programmed cells and errors
Solution Approach 1:
The patent applies preliminary action by performing a detection read operation after programming but before normal operation. This detection step proactively identifies under-programmed cells caused by word line defects, preventing future errors. The method prepares the system by catching defects early when they manifest as threshold voltage mismatches, rather than waiting for operational failures.
Solution Approach 2:
The patent implements feedback by comparing the actual threshold voltage of programmed cells against expected values. When mismatches are detected, the system generates feedback signals to identify and flag defective word lines. This feedback mechanism enables continuous monitoring and automatic detection of programming errors without additional hardware latches.
2Productivity
If traditional programming verification is used, then programming speed is maintained, but word line defects with slight resistance increases remain undetected
Solution Approach 1:
The patent merges the detection function with existing programming verification infrastructure. By reusing the same read circuits and threshold voltage measurement mechanisms already present in the memory system, the method combines programming and detection operations without requiring separate dedicated detection hardware. This merging approach maintains programming speed while adding defect detection capability.
Solution Approach 2:
The patent applies universality by designing the detection mechanism to use the same multi-state programming verification infrastructure already present in the system. The detection method works across multiple programming states and leverages existing read circuits, making the defect detection capability universal rather than state-specific or hardware-additive.
3Measurement precision
If additional data latches are added to detect under-programmed cells, then defect detection accuracy improves, but device complexity and cost increase
Solution Approach 1:
The patent applies self-service by enabling the memory system to detect its own defects using its existing resources. The detection method utilizes the memory's own read circuits, threshold voltage measurement capabilities, and programming verification infrastructure to identify under-programmed cells. No external or additional dedicated detection hardware is required—the system serves its own detection needs.
Solution Approach 2:
The patent discards the need for additional data latches by recovering and reusing existing verification infrastructure. Instead of adding new hardware components, the method recovers the utility of existing read circuits and threshold voltage measurement mechanisms, using them for defect detection purposes alongside their traditional programming verification role.
Data Source
AI summary
Methods and non-volatile storage systems are provided for detecting defects in word lines. A “broken” word line defect may be detected. Information may be maintained as to which storage elements were intended to be programmed to a tracked state. Then, after programming is complete, the storage elements are read to determine which storage elements have a threshold voltage below a reference voltage level associated with the tracked state. By tracking which storage elements are in the tracked state, elements associated with other states may be filtered out such that an accurate assessment may be made as to which storage elements were under-programmed. From this information, a determination may be made whether the word line is defective. For example, if too many storage elements are under-programmed, this may indicate a broken word line.