AlN/SiC Submount for Semiconductor Lasers
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Solution Overview
Problem
The thermal expansion coefficient mismatch between silicon carbide (SiC) and indium phosphide (InP) materials in semiconductor lasers leads to mechanical stress and reduced reliability, especially during thermal cycles, limiting the use of SiC as a submount material despite its superior thermal conductivity.
Innovation Solution
A submount comprising a layer of silicon carbide (SiC) with a thin layer of aluminum nitride (AlN) deposited on top, acting as a buffer to absorb mechanical stress, and bonded with gold-tin (AuSn) eutectic solder to minimize strain transmission to the laser, while maintaining high thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If diamond is used as submount material to achieve high thermal conductivity, then heat removal efficiency is improved, but CTE mismatch causes mechanical stress and reduced reliability
Solution Approach 1:
The patent introduces an intermediate AlN layer between the diamond submount and the InP-based laser chip. This AlN layer acts as a CTE-matched intermediary material that absorbs thermal expansion differences, preventing mechanical stress from being transmitted to the laser facets while maintaining the high thermal conductivity pathway provided by the diamond substrate.
Solution Approach 2:
The patent creates a composite submount structure combining diamond and AlN layers. The diamond layer provides superior thermal conductivity for heat removal, while the AlN layer provides CTE matching to the InP-based laser material. This composite structure integrates the beneficial properties of both materials to simultaneously achieve high heat removal efficiency and mechanical stress-free operation.
2Temperature
If SiC is used as submount material to achieve high thermal conductivity, then heat removal efficiency is improved, but CTE mismatch still causes mechanical stress during thermal cycles
Solution Approach 1:
The patent introduces an intermediate AlN layer between the SiC submount and the InP-based laser chip. This AlN layer acts as a CTE-matched intermediary material that absorbs thermal expansion differences, preventing mechanical stress from being transmitted to the laser facets while maintaining the high thermal conductivity pathway provided by the SiC substrate.
Solution Approach 2:
The patent creates a composite submount structure combining SiC and AlN layers. The SiC layer provides superior thermal conductivity for heat removal, while the AlN layer provides CTE matching to the InP-based laser material. This composite structure integrates the beneficial properties of both materials to simultaneously achieve high heat removal efficiency and mechanical stress-free operation.
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 AlN/SiC submount configuration reduces the average active region temperature of semiconductor lasers by approximately 4-10 K, enhancing laser performance and reliability by suppressing thermal-induced mechanical stress and maintaining low thermal resistance.
Implementation Method 1
The CTE mismatch between InP and diamond is very large... the CTE mismatch between SiC and InP can be less than 1.0×10−6... The AlN layer serves as a buffer that absorbs mechanical stress caused by the residual CTE mismatch
Implementation Method 2
SiC has a thermal conductivity of up to 600 W/mK, three times that for AlN... Diamond has the highest known thermal conductivity (>1800 W/mK)... the presence of this AlN buffer layer will not significantly increase the overall thermal resistance
Implementation Method 3
for laser bonding, we used an AuSn eutectic solder system... bonded with gold-tin (AuSn) eutectic solder
Data Source
AI summary
A submount for a semiconductor laser. The submount has a layer of silicon carbide (SiC) and a layer of aluminum nitride (AlN) deposited on the layer of SiC. The submount is bonded to the InP-based laser by a hard solder applied to the AlN layer. Preferably, the thickness of the AlN layer is ten to twenty microns, the thickness of the SiC layer is two hundred fifty microns, and the solder is a gold-tin (AuSn) eutectic. The semiconductor laser may be a quantum cascade laser (QCL). Similar combinations of submount materials can be found for other semiconductor laser material systems and types.