Waveguides with Multiple-Level Airgaps for Mid-Infrared Signal Loss
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Solution Overview
Problem
Silicon waveguides in photonic chips experience signal loss due to strong absorption of electromagnetic radiation by the silicon dioxide cladding layer in the mid-infrared wavelength range, particularly starting at 3.5 μm, which affects on-chip communication and sensing applications.
Innovation Solution
A waveguide structure is fabricated using a bulk semiconductor substrate with epitaxial semiconductor layers and trench isolation regions, incorporating airgaps in both the substrate and dielectric layers to reduce signal loss, with the airgaps arranged under and over the waveguide core region to minimize absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon dioxide cladding is used to surround the waveguide core, then the waveguide structure is complete and mechanically stable, but signal loss increases due to strong absorption of electromagnetic radiation at wavelengths above 3.5 μm
Solution Approach 1:
The patent removes the silicon dioxide cladding material from direct contact with the waveguide core in the mid-infrared wavelength range by introducing airgaps. The airgap acts as an extraction of the harmful absorbing material, replacing it with air that has minimal absorption in the 3-8 μm range, thereby reducing signal loss while maintaining structural integrity through the trench isolation regions.
Solution Approach 2:
The patent applies different material properties to different regions: the waveguide core region has airgaps on both sides to minimize absorption for light propagation, while the trench isolation regions provide mechanical support and electrical isolation. This local differentiation allows the waveguide to have low loss in the optical path while maintaining overall structural stability.
2Loss of energy
If airgaps are introduced to reduce signal loss, then transparency in the mid-infrared range improves, but device complexity increases due to multiple fabrication steps
Solution Approach 1:
The patent divides the airgap formation into two separate segments: a first airgap formed in the substrate beneath the waveguide core, and a second airgap formed in the dielectric layer above the waveguide core. This segmentation allows each airgap to be formed using optimized fabrication processes independent of each other, making the overall complex structure achievable through modular fabrication steps.
Solution Approach 2:
The patent performs preliminary actions by forming the first airgap in the substrate before epitaxial growth of the semiconductor layer, and forming the second airgap in the dielectric layer after waveguide formation. These preliminary airgap structures are prepared in advance to guide subsequent fabrication steps and ensure proper positioning, reducing overall process complexity despite the multiple steps involved.
3Loss of energy
If the volume of silicon dioxide surrounding the waveguide core is reduced, then absorption is minimized and transparency enhances, but manufacturing precision requirements increase
Solution Approach 1:
The patent introduces intermediary structures to facilitate airgap formation: the trench isolation regions serve as intermediaries that define the boundaries of the waveguide core and guide the formation of airgaps on either side. These intermediary structures provide reference features that simplify the positioning process and reduce the precision requirements compared to direct airgap formation without guides.
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 airgap structure reduces signal loss by minimizing the volume of silicon dioxide surrounding the waveguide core, thereby reducing absorption and enhancing the transparency of the waveguide in the mid-infrared range, improving the performance of photonic chips in data communication and sensing systems.
Implementation Method 1
silicon waveguides may experience signal loss because the silicon dioxide layer cladding the waveguide strongly absorbs electromagnetic radiation starting at a wavelength of 3.5 μm
Data Source
AI summary
Waveguide structures and methods of fabricating waveguide structures. A first airgap is formed in a bulk semiconductor substrate, and a semiconductor layer is epitaxially grown over the bulk semiconductor substrate and the first airgap. First and second trench isolation regions extend through the semiconductor layer and into the bulk semiconductor substrate, and are spaced to define a waveguide core region including a section of the bulk semiconductor substrate and a section of the semiconductor layer that are arranged between the first and second trench isolation regions. A dielectric layer is formed over the waveguide core region, and a second airgap is formed in the dielectric layer. The first airgap is arranged in the bulk semiconductor substrate between the first trench isolation region and the second trench isolation region and under the waveguide core region. The second airgap in the dielectric layer is arranged over the waveguide core region.