SiN Waveguide Edge Coupler for CMOS PIC Refractive Index Matching
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Solution Overview
Problem
The formation of waveguide edge couplers in photonics integrated circuits (PICs) is challenging due to the varying refractive index of back-end-of-line (BEOL) insulating layers, which affects optimal refractive index matching for efficient optical communication with fiber optic cables, and silicon waveguide edge couplers face power handling and fabrication tolerance issues.
Innovation Solution
A silicon nitride (SiN) waveguide edge coupler is integrated into the photonics region of a PIC, positioned over a buried insulator layer and at least partially under the BEOL insulator stack, with an oxide layer extending over the BEOL insulator stack, and a V-groove or squared groove is defined in the semiconductor substrate for optimal fiber optic cable mounting, enabling improved optical communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon waveguide edge couplers are used, then optical communication with fiber optic cables is enabled, but power handling and fabrication tolerance issues arise
Solution Approach 1:
The patent changes the material parameter from silicon to silicon nitride, which fundamentally alters the refractive index characteristics. This parameter change enables the waveguide to achieve optimal refractive index matching with BEOL insulating layers while providing superior fabrication tolerance and power handling capabilities, directly resolving the contradiction between optical communication performance and manufacturing precision
Solution Approach 2:
The patent employs silicon nitride as a composite material solution that combines the beneficial properties of having a可调 refractive index (comparable to BEOL insulators) with enhanced fabrication tolerance and power handling. This material selection creates a composite structure that simultaneously addresses multiple performance requirements that silicon alone cannot satisfy
2Adaptability or versatility
If BEOL insulator stack is present in photonics region, then CMOS integration is achieved, but refractive index matching for waveguide edge coupler becomes challenging
Solution Approach 1:
The patent changes the waveguide material parameter to silicon nitride, which has a refractive index that can be optimally matched to BEOL insulating layers. This parameter change enables the system to maintain CMOS integration capability while achieving the refractive index matching necessary for efficient waveguide edge coupler operation
Solution Approach 2:
The silicon nitride waveguide acts as an intermediary structure between the CMOS region with BEOL insulators and the optical fiber. By positioning the silicon nitride waveguide edge coupler at the interface and using its specific refractive index properties, it mediates the optical coupling while being compatible with the overlying BEOL insulator stack, thus enabling both CMOS integration and optimal optical performance
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 SiN waveguide edge coupler provides enhanced optical communication with fiber optic cables, overcoming the limitations of silicon waveguide edge couplers by ensuring better refractive index matching and improved fabrication tolerance, thus enhancing the optical performance of the PIC.
Implementation Method 1
a silicon nitride (SiN) waveguide edge coupler positioned in a first region over the buried insulator layer and at least partially under the BEOL insulator stack
Implementation Method 2
Due to their varying refractive index, the BEOL insulating layers in the photonics region can make it a challenge to form a waveguide edge coupler
Data Source
AI summary
A photonics integrated circuit includes a semiconductor substrate; a buried insulator layer positioned over the semiconductor substrate; and a back-end-of-line (BEOL) insulator stack over a first portion of the buried insulator layer. In addition, the PIC includes a silicon nitride (SiN) waveguide edge coupler positioned in a first region over the buried insulator layer and at least partially under the BEOL insulator stack. An oxide layer extends over a side of the BEOL insulator stack. The SiN waveguide edge coupler provides better power handling and fabrication tolerance than silicon waveguide edge couplers, despite the location under various BEOL layers. The PIC can also include silicon waveguide edger coupler(s).