Chamfered Mesa VCSEL for Moisture Resistance
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Solution Overview
Problem
Surface-emitting lasers face challenges in moisture resistance due to defects in the insulating films covering the VCSEL chips, which can lead to corrosion.
Innovation Solution
A surface-emitting laser design featuring a mesa with a polygonal shape and chamfered vertices, covered by multiple insulating films, including a denser silicon nitride passivation film, to enhance moisture resistance and reduce defects in the film coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single insulating film is used to cover the VCSEL chip, then the manufacturing process is simple, but moisture can enter through defects in the insulating film causing corrosion
Solution Approach 1:
The patent applies composite materials by using multiple insulating films with different properties (silicon oxide film and silicon nitride film) stacked together. The silicon oxide film provides good interface characteristics with the semiconductor layer, while the silicon nitride film provides high density and excellent moisture barrier properties. This composite structure resolves the contradiction by achieving superior moisture resistance without requiring a single complex material.
Solution Approach 2:
The patent segments the insulating film into multiple distinct layers, each performing a specific function. The first insulating film (silicon oxide) covers the semiconductor layers and provides a good interface, while the second insulating film (silicon nitride) covers the first film and provides the primary moisture barrier. This segmentation allows each layer to be optimized for its specific role, resolving the contradiction between simplicity and reliability.
2Manufacturing precision
If the mesa has sharp vertices, then the manufacturing process is simpler, but the insulating film coverage is poor leading to defects
Solution Approach 1:
The patent applies preliminary action by forming chamfered portions at the vertices of the mesa before depositing the insulating films. This pre-processing step creates a favorable surface geometry that ensures proper insulating film coverage at the vertices, preventing defects without complicating the overall manufacturing process. The chamfering is performed as a preliminary step that facilitates subsequent film deposition.
Solution Approach 2:
The patent changes the geometric parameter of the mesa vertices from sharp corners to chamfered surfaces. This parameter change (creating an inclined surface at the vertices) improves the coverage of insulating films by providing a surface that allows proper film adhesion and continuity, eliminating the coverage defects that would occur with sharp vertices.
3Ease of operation
If the insulating film is removed outside the mesa, then the substrate is exposed for further processing, but moisture can enter through the exposed areas
Solution Approach 1:
The patent applies dimensionality change by extending the insulating films not only in the planar dimension but also in the vertical dimension beyond the mesa boundaries. The insulating films cover the side surfaces of the mesa and extend onto the substrate, creating a three-dimensional protective barrier. This allows the substrate to be accessible for processing while simultaneously preventing moisture intrusion through the exposed areas.
Solution Approach 2:
The patent uses thin insulating films to create a flexible protective barrier that conforms to the mesa structure and extends onto the substrate. These thin films provide effective moisture protection while allowing the substrate to remain accessible for further processing operations. The films act as a protective shell that can be configured to meet both accessibility and protection requirements.
Data Source
AI summary
A surface-emitting laser includes a substrate; semiconductor layers provided on the substrate, the semiconductor layers including a lower reflector layer, an active layer, and an upper reflector layer, the semiconductor layers forming a mesa; a first insulating film covering the mesa; and a second insulating film covering the first insulating film, wherein the mesa has a polygonal shape in a direction in which the substrate extends, and a vertex of the mesa in the direction in which the substrate extends has a chamfered portion.