Silicon Waveguide on Bulk Substrate with Air Gaps
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Solution Overview
Problem
Conventional silicon-on-insulator (SOI) substrates used in IC photonic devices are expensive, making them less practical due to their high cost and complexity, despite providing efficient optical properties through a thick buried oxide layer.
Innovation Solution
The development of silicon-based optical devices formed on bulk silicon substrates using a method that involves forming trenches, undercut etching, and partially filling cavities with a dielectric to create air gaps, reducing material costs and complexity while maintaining low-loss optical light transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional SOI substrates with thick buried oxide layers are used, then low-loss optical light transmission is achieved, but manufacturing cost and device complexity increase significantly
Solution Approach 1:
The patent divides the substrate structure into distinct functional layers: a simplified bulk silicon substrate base, selective cavity regions etched into the substrate, and dielectric filling material. This segmentation allows the optical waveguide function to be achieved through localized structural modifications rather than requiring a complex thick buried oxide layer throughout the entire substrate, thereby reducing manufacturing cost while maintaining optical performance.
Solution Approach 2:
The patent applies local quality by creating cavities only in specific regions where optical waveguides are needed, rather than using a uniform thick buried oxide layer across the entire substrate. The cavities are selectively filled with dielectric material to provide the necessary optical confinement only where required. This localized approach maintains low-loss optical transmission in critical areas while simplifying the overall substrate structure and reducing manufacturing complexity in non-critical areas.
2Loss of energy
If conventional SOI substrates are used, then efficient optical properties are maintained, but material costs increase
Solution Approach 1:
The patent replaces the expensive conventional SOI substrate with a cheaper bulk silicon substrate. The simplified substrate structure uses readily available bulk silicon material rather than costly processed SOI wafers with thick buried oxide layers. This substitution significantly reduces material costs while the selective cavity and dielectric filling structures provide the necessary optical functionality at a fraction of the material cost.
3Device complexity
If bulk silicon substrates are used instead of SOI substrates, then manufacturing cost is reduced, but optical confinement capability must be maintained through alternative structures
Solution Approach 1:
The patent transitions from relying on vertical thickness (the thick buried oxide layer in conventional SOI) to achieving optical confinement through lateral dimensional control. The cavities are etched to specific depths and widths, and the dielectric filling material provides optical confinement through lateral boundaries rather than relying solely on vertical layer thickness. This dimensional shift allows optical functionality to be achieved on a simplified bulk silicon substrate without requiring complex thick oxide layers.
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 reduces the material costs and complexity of manufacturing IC optical devices while maintaining efficient optical properties, offering a cost-effective alternative to conventional SOI substrates by utilizing bulk silicon substrates and creating silicon waveguide structures with air gaps surrounded by dielectric, enhancing flexibility in integrating CMOS FETs.
Implementation Method 1
undercut etching the silicon substrate in a direction perpendicular to the crystal direction of the silicon substrate to form a cavity corresponding with each of the first set of trenches
Data Source
AI summary
Various methods include: forming a first set of trenches in a precursor structure having: a silicon substrate having a crystal direction, the silicon substrate substantially abutted by a first oxide; a silicon germanium (SiGe) layer overlying the silicon substrate; a silicon layer overlying the SiGe layer; a second oxide overlying the silicon layer; and a sacrificial layer overlying the second oxide, wherein the first set of trenches each expose the silicon substrate and internal sidewalls of the first oxide; undercut etching the silicon substrate in a direction perpendicular to the crystal direction of the silicon substrate to form a cavity corresponding with each of the first set of trenches; and partially filling each cavity with a dielectric, leaving an air gap within each cavity connected with an air gap in an adjacent cavity.