AlN Sub-mount Stress Optimization for Laser Polarizing Angle
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Solution Overview
Problem
Conventional semiconductor light emitting devices experience significant residual stress due to differences in linear expansion coefficients between the semiconductor laser substrate and the package material, leading to a large polarizing angle of the laser, which affects the stability and yield of the device, especially in varying temperature environments and multi-wavelength laser systems.
Innovation Solution
A semiconductor light emitting device is designed with a sub-mount where the thickness and width are optimized to ensure that the product of equivalent stress and stress in the width direction does not exceed 70% of the maximum value, reducing residual stress and thereby minimizing the polarizing angle of the laser.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a sub-mount is inserted between the package and the semiconductor laser to reduce residual stress, then the mechanical strength is improved and some stress is reduced, but the polarizing angle of the laser becomes large due to remaining stress in the waveguide
Solution Approach 1:
The patent changes the material parameter of the sub-mount from conventional materials (Si, AlN) to a composite material consisting of an aluminum plate with a specific aluminum nitride coating layer. This material parameter change allows for better stress management while maintaining mechanical strength, thereby reducing the polarizing angle caused by residual stress in the waveguide.
Solution Approach 2:
The patent employs a composite material structure for the sub-mount, combining an aluminum plate substrate with an aluminum nitride coating layer. This composite structure leverages the high thermal conductivity and mechanical strength of aluminum while the aluminum nitride layer provides stress management properties, effectively reducing residual stress-induced polarizing angle without compromising structural integrity.
2Stress or pressure
If the composition of solder or material for the sub-mount is changed to lower residual stress, then the stress is reduced, but the polarizing angle remains large due to stress concentration in the waveguide region
Solution Approach 1:
The patent modifies the material parameters of the sub-mount by using a composite structure (aluminum plate with aluminum nitride coating) rather than changing solder composition. This approach reduces residual stress more effectively while preventing stress concentration in the waveguide region, thereby reducing the polarizing angle that persists even with solder composition changes.
Solution Approach 2:
The aluminum nitride coating layer on the aluminum plate sub-mount acts as an intermediary that mediates between the package and the semiconductor laser chip. This intermediate layer distributes stress more evenly, preventing stress concentration in the waveguide region that occurs with conventional solder or sub-mount material changes alone.
3Stress or pressure
If the laser chip is protruded from the sub-mount to relax stress in the vicinity of the light-emitting point, then some stress relaxation is achieved, but the polarizing angle becomes large due to stress in the waveguide
Solution Approach 1:
The patent changes the fundamental parameter of the sub-mount material to a composite aluminum plate with aluminum nitride coating, which provides inherent stress management properties. This eliminates the need for chip protrusion while effectively reducing polarizing angle by preventing stress concentration in the waveguide, unlike the protrusion method that only relaxes stress locally at the light-emitting point.
4Ease of manufacture
If conventional sub-mount materials like Si are used, then the manufacturing is simplified, but the residual stress is large compared to AlN sub-mounts, causing large polarizing angle
Solution Approach 1:
The patent uses a composite material (aluminum plate with aluminum nitride coating) that combines the manufacturing advantages of aluminum with the stress-management properties of aluminum nitride. This composite approach achieves better polarizing angle control than pure AlN while maintaining ease of manufacture through established coating technologies on aluminum substrates.
Solution Approach 2:
The patent optimizes the material parameters by selecting a composite structure where the aluminum plate provides mechanical properties and the aluminum nitride coating provides stress management. This parameter optimization achieves low polarizing angle without the manufacturing complexity of pure AlN, balancing ease of manufacture with performance.
5Ease of manufacture
If the thickness and width of the sub-mount are not optimized, then the manufacturing is simpler, but the product of equivalent stress and stress in the width direction exceeds 70% of the maximum value, causing large polarizing angle
Solution Approach 1:
The patent optimizes the geometric parameters (thickness and width) of the sub-mount to control the product of equivalent stress and stress in the width direction. By carefully selecting these dimensions, the patent achieves effective stress management and polarizing angle reduction while maintaining manufacturing simplicity through standard fabrication tolerances.
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 effectively reduces the polarizing angle of the laser, enhancing the stability and yield of the semiconductor light emitting device by minimizing stress-induced variations with temperature changes and allowing for better adjustment of polarizing angles in multi-wavelength systems.
Implementation Method 1
the coefficient of linear expansion of GaAs is 6 (×10−6/° C.), the coefficient of linear expansion of Fe is 11 (×10−6/° C.), and the coefficient of linear expansion of Cu is 17 (×10−6/° C.). Therefore, when the semiconductor laser having a GaAs substrate is directly adhered to an Fe package with solder or the like, residual stress occurs due to difference in coefficients of linear expansion
Data Source
AI summary
A semiconductor laser chip is joined to an AlN sub-mount in a junction-down manner. The sub-mount is joined to a package. The AlN sub-mount is joined to a stem. The direction perpendicular to the irradiation direction of a laser beam emitted from the semiconductor laser chip is the direction of the width of the sub-mount. The thickness and the width of the AlN sub-mount are determined so that the product of the equivalent stress applied to the center of the surface of the semiconductor laser chip joined to the sub-mount and the stress in the direction of the width of the sub-mount does not exceed 70% of the maximum value of the product obtained by changing the thickness and the width of the AlN sub-mount.