eFuse Macro Switching Unit for Abnormal Resistance Detection
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Solution Overview
Problem
Conventional eFuse macros face challenges in accurately distinguishing between blown and unblown fuses due to abnormal resistance variations, leading to increased defective parts per million (DPPM), as the resistance of blown fuses can be similar to that of unblown fuses due to process variations or other factors.
Innovation Solution
The eFuse macro incorporates a switching unit with different resistances in normal and test modes, utilizing a reference resistor and a verifying resistor to generate output signals indicating whether a fuse is blown or not, thereby providing a serious condition to screen out blown fuses with marginal fail resistance without increasing testing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sensing methods are used to determine fuse state, then the sensing circuit is simple, but the measurement precision deteriorates when fuse resistance is abnormal due to process variations
Solution Approach 1:
The sensing circuit dynamically switches between normal mode and test mode based on the state of the switching unit. In normal mode, the circuit operates with standard sensing parameters. When the switching unit detects an abnormal condition (such as marginal fail resistance), it transitions to test mode where the resistance of the switching unit changes to provide a more distinguishable sensing condition, thereby improving measurement precision for abnormal fuses without requiring a completely different circuit design
Solution Approach 2:
The invention changes the resistance parameter of the switching unit between normal mode and test mode. By adjusting the resistance of the switching unit, the sensing circuit can adapt to different fuse states. In test mode, the switching unit's resistance is modified to create a more significant resistance difference between blown and unblown fuses, improving the ability to detect abnormal fuse states while maintaining circuit simplicity
2Measurement precision
If additional testing procedures are implemented to screen marginal fail fuses, then the measurement precision improves, but the loss of time increases
Solution Approach 1:
The sensing process is divided into periodic phases: normal mode operation for routine sensing and test mode for periodic verification. The switching unit enables periodic transition to test mode where marginal fail fuses are screened with enhanced precision. This periodic action allows accurate detection of abnormal fuses while maintaining fast normal operation, as the test mode is only activated when needed rather than continuously
Solution Approach 2:
The switching unit is pre-configured to enable rapid transition between normal and test modes. The circuit is designed with preliminary switching mechanisms that allow immediate mode change without extensive reconfiguration, reducing the time penalty for performing additional testing. The test mode capability is prepared in advance, allowing quick screening of marginal fail fuses when triggered
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves DPPM by accurately differentiating between blown and unblown fuses, even with abnormal resistance, without extending testing time, by employing resistors that provide distinct conditions in normal and test modes.
Implementation Method 1
An eFuse may be programmed by applying a relatively large amount of power (e.g. a current with sufficient magnitude and duration) to the fuse to be programmed, so as to melt and separate the fuse body material
Implementation Method 2
According to the resistance of the eFuse, the state of the eFuse is sensed to determine whether the eFuse is blown or not
Data Source
AI summary
An eFuse with at least one fuse unit is provided. The fuse unit includes a first common node providing a first reference voltage, a second common node providing a second reference voltage, at least one fuse coupled to the first common node, and a determining unit coupled between the fuse and the second common node, generating an output signal indicating whether the fuse is blown or not according to a first condition in a normal mode and a second condition in a test mode.