Testkey Switching Circuits Reduce Leakage Current
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Solution Overview
Problem
In semiconductor fabrication, the sub-threshold leakage current from untested devices can significantly impact the accuracy of wafer acceptance testing, as multiple devices share common test pads, leading to interference and reduced test precision.
Innovation Solution
A testkey system incorporating switching circuits that isolate untested devices by functioning as high impedance and compensation circuits that provide current to reduce leakage when devices are not being tested, ensuring accurate measurement of tested devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If addressable transistor arrays with common test pads are used to measure large quantity of transistors within limited space, then testing efficiency and space utilization are improved, but leakage current from untested devices increases and test accuracy deteriorates
Solution Approach 1:
The patent divides the common test pad system into multiple isolated test paths by introducing switching circuits for each transistor. Each transistor gets its own dedicated test path controlled by address signals, segmenting the previously shared test pad into multiple isolated measurement channels. This segmentation prevents leakage current from untested transistors from affecting the measurement of the tested transistor, thereby maintaining high testing efficiency while improving measurement accuracy.
2Area of stationary object
If multiple devices share common test pads, then device density and space utilization are improved, but leakage current interference between devices increases
Solution Approach 1:
The patent introduces switching circuits as intermediary elements between the common test pad and individual transistors. These switching circuits act as mediators that control the connection between the shared test pad and each transistor based on address signals. When a specific transistor is being tested, its switch closes to establish a low-impedance path, while other switches remain open to isolate their leakage currents. This intermediary mechanism enables high device density while preventing leakage current interference.
3Measurement precision
If switching circuits are used to isolate untested devices, then test accuracy is improved, but circuit complexity increases
Solution Approach 1:
The patent designs the switching circuits with multi-functionality to reduce overall system complexity. Each switching circuit not only performs the isolation function but also participates in the addressing mechanism and test signal routing. The same switching infrastructure is used for both isolation and signal transmission, eliminating the need for separate isolation circuits. This universal approach improves test accuracy while minimizing the increase in circuit complexity.
Data Source
AI summary
A testkey includes two switching circuits and two compensation circuits. The first switching circuit transmits a test signal to a first DUT when the first DUT is being tested and functions as high impedance when the first DUT is not being tested. The second switching circuit transmits the test signal to a second DUT when the second DUT is being tested and functions as high impedance when the second DUT is not being tested. When the first DUT is not being tested and the second DUT is being tested, the first compensation circuit provides first compensation current for reducing the leakage current of the first switching circuit. When the first DUT is being tested and the second DUT is not being tested, the second compensation circuit provides second compensation current for reducing the leakage current of the second switching circuit.