Semiconductor Laser Pad Structure for Solder Diffusion Control
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Solution Overview
Problem
Existing semiconductor lasers face challenges in achieving high reliability due to solder diffusion issues during junction-down mounting, which can lead to heat-related output saturation and degradation, despite the use of barrier materials like molybdenum and titanium.
Innovation Solution
A semiconductor laser design that includes a substrate, first and second cladding layers, an active layer, and a pad metal structure where the upper and side portions of the pad metal are covered with an insulating film and barrier metal, with the barrier metal and bonding metal sequentially deposited on the pad metal, enhancing heat dissipation and preventing solder diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If junction-down mounting is used to improve heat dissipation, then heat dissipation performance is improved, but solder diffusion to the electrode occurs causing reliability degradation
Solution Approach 1:
The protective coating is segmented into multiple layers: a lower barrier metal layer (Ti, Mo, W) that provides solder diffusion barrier, and an upper insulating film layer (SiO2, Si3N4) that provides additional protection. This segmentation allows each layer to perform its specific function optimally while working together to prevent solder diffusion during junction-down mounting.
Solution Approach 2:
The barrier metal and insulating film act as intermediary protective layers between the electrode and the solder. These intermediary layers prevent direct contact between the solder and the electrode, thereby preventing solder diffusion while allowing the heat dissipation function to be maintained through proper thermal design.
2Reliability
If barrier metal layers are added to prevent solder diffusion, then reliability is improved, but device complexity increases
Solution Approach 1:
The harmful function of solder diffusion is extracted and isolated from the electrode by introducing dedicated barrier layers. The barrier metal and insulating film are specifically designed to take out the protective function from the overall device structure, allowing the electrode to maintain its original electrical and optical functions while the barrier layers handle the protective function.
3Reliability
If the pad metal surface is fully covered with protective layers, then solder diffusion is prevented, but heat dissipation efficiency decreases
Solution Approach 1:
The protective coating is applied with local quality consideration: the barrier metal layer is positioned at the lower portion of the pad metal where solder diffusion is most likely to occur, while the insulating film covers the upper portion. This localized protection approach prevents solder diffusion at critical areas while minimizing the impact on heat dissipation pathways.
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 proposed design significantly improves the reliability of semiconductor lasers by effectively preventing solder diffusion and heat-related degradation, maintaining high output performance and extending the lifespan of the device.
Implementation Method 1
an upper portion of the pad metal on a side of the pad metal opposite to a side closer to the substrate and a side portion of the pad metal are covered with an insulating film and barrier metal
Implementation Method 2
the barrier metal and a bonding metal are disposed in this order on the pad metal on the side of the pad metal opposite to the side closer to the substrate
Implementation Method 3
a substrate, a first cladding layer of a first conductivity type, an active layer, a second cladding layer of a second conductivity type, and a pad metal in this order
Data Source
AI summary
To provide a semiconductor laser capable of further improving reliability. Provided is a semiconductor laser including a substrate, a first cladding layer of a first conductivity type, an active layer, a second cladding layer of a second conductivity type, and a pad metal in this order, in which an upper portion of the pad metal on a side of the pad metal opposite to a side closer to the substrate and a side portion of the pad metal are covered with an insulating film and a barrier metal, and the barrier metal and a bonding metal are disposed in this order on the pad metal on the side of the pad metal opposite to the side closer to the substrate.