Composite Passivation Layer for High-Speed Laser Diodes
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Solution Overview
Problem
High-speed semiconductor lasers face mechanical stress issues due to thick passivation layers, which can lead to cracking and damage, compromising their integrity and performance in high data rate applications.
Innovation Solution
A composite passivation layer with a silicon nitride bottom and top layer and a silicon dioxide middle layer is used, with differing stress components that cancel out overall mechanical stress, allowing for thicker layers without increasing the risk of cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the passivation layer thickness is increased to reduce parasitic capacitance for high-speed operation, then the laser's electrical performance is improved, but mechanical stress increases causing cracking and device failure
Solution Approach 1:
The passivation layer is divided into multiple sub-layers (first passivation layer, second passivation layer, third passivation layer) with different stress characteristics. This segmentation allows each layer to contribute differently to the overall stress profile, enabling the total thickness to be sufficient for reducing parasitic capacitance while the combined stress remains controlled and prevents cracking.
Solution Approach 2:
The invention changes the stress parameter distribution within the passivation layer by using materials with different stress properties for each sub-layer. By controlling the thickness and material composition of each layer, the overall stress state is optimized to prevent mechanical failure while maintaining the necessary total thickness for high-speed electrical performance.
2Object-affected harmful factors
If a thick passivation layer is used to adequately protect against parasitic capacitance, then electrical isolation is improved, but mechanical stress causes layer rupture and contamination
Solution Approach 1:
The passivation structure is segmented into multiple layers with different stress characteristics. This allows the total thickness to be increased for better electrical isolation and parasitic capacitance reduction, while the distributed stress across layers prevents any single layer from experiencing stress concentrations that would cause rupture.
Solution Approach 2:
The invention uses composite material structure with different passivation layer materials that have complementary properties. The combination of materials with different stress characteristics creates a composite structure that achieves both the necessary thickness for electrical protection and the stress distribution needed to prevent mechanical failure.
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 composite passivation layer effectively reduces parasitic capacitance and mechanical stress, enabling high-speed laser operation without layer stress cracking, thus preserving the integrity and structure of the laser device.
Implementation Method 1
The passivation layers possess differing stress components that, when combined, cancel out the overall mechanical stress of the passivation layer
Data Source
AI summary
A laser diode having a composite passivation layer configured to control parasitic capacitance, especially in high speed laser applications, is disclosed. In one embodiment, a ridge waveguide laser is disclosed and includes: a substrate, an active layer disposed on the substrate, a ridge structure disposed on the active layer, and a contact layer disposed on the ridge structure. A composite passivation layer is disposed substantially laterally to the ridge structure. The composite passivation layer includes a silicon nitride bottom layer, a silicon nitride top layer, and a silicon dioxide middle layer interposed between the bottom and top layers. The passivation layers possess differing stress components that, when combined, cancel out the overall mechanical stress of the passivation layer. This enables relatively thick passivation layers to be employed in high speed laser diodes without increasing the risk of layer stress cracking and laser damage.