Stress-Relieving Layer for Semiconductor Emitter Thermal Management
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Solution Overview
Problem
Heterojunction bipolar transistors in semiconductor devices experience thermal stress due to differences in thermal expansion coefficients between redistribution lines and semiconductor layers, leading to degraded transistor characteristics and reduced reliability.
Innovation Solution
Incorporating a stress-relieving layer made of high-melting-point metals like tungsten or molybdenum between the emitter redistribution layer and the emitter layer, which reduces thermal stress by matching the thermal expansion coefficient of the semiconductor layers, thereby alleviating the strain caused by temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a redistribution line (e.g., copper) is disposed over an emitter electrode to improve electrical connection, then electrical conductivity is improved, but thermal stress increases due to difference in thermal expansion coefficient between the redistribution line and semiconductor layer
Solution Approach 1:
A stress-relieving layer is introduced as an intermediary between the emitter redistribution layer and the emitter layer. This intermediate layer has a thermal expansion coefficient that matches the semiconductor layer, thereby mediating the thermal stress caused by the copper redistribution line and preventing degradation of the emitter layer.
Solution Approach 2:
The patent employs a composite structure consisting of multiple layers with different material properties. The stress-relieving layer is made of a material specifically selected to have thermal expansion properties compatible with the semiconductor layer, creating a composite system that balances electrical conductivity requirements with thermal stress management.
2Stress or pressure
If a stress-relieving layer is added between the emitter redistribution layer and the emitter layer to reduce thermal stress, then thermal stress on the emitter layer is reduced, but device structure becomes more complex
Solution Approach 1:
The patent addresses the contradiction by changing the material parameter (thermal expansion coefficient) of the stress-relieving layer to match that of the semiconductor layer. This parameter matching approach effectively reduces thermal stress while maintaining a relatively simple structural configuration, as the added layer integrates seamlessly with the existing stack.
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
The stress-relieving layer effectively decreases thermal stress on the emitter layers, enhancing the reliability and radio-frequency performance of the bipolar transistors by preventing premature degradation and maintaining current amplification factors.
Implementation Method 1
the difference in thermal expansion coefficient between the redistribution line and a semiconductor layer such as an emitter layer would result in a thermal stress on the emitter layer
Data Source
AI summary
A semiconductor device includes a semiconductor element including a bipolar transistor disposed on a compound semiconductor substrate, a collector electrode, a base electrode, and an emitter electrode, the bipolar transistor including a collector layer, a base layer, and an emitter layer, the collector electrode being in contact with the collector layer, the base electrode being in contact with the base layer, the emitter electrode being in contact with the emitter layer; a protective layer disposed on one surface of the semiconductor element; an emitter redistribution layer electrically connected to the emitter electrode via a contact hole in the protective layer; and a stress-relieving layer disposed between the emitter redistribution layer and the emitter layer in a direction perpendicular to a surface of the compound semiconductor substrate.