Sawtooth Grating Couplers with BEOL Stack Integration
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Solution Overview
Problem
Grating couplers in integrated optics suffer from limited bandwidth and coupling efficiency due to dispersive operating principles and additional reflections caused by non-optimized top cladding materials like nitride, which reduces the overall performance of photonic devices.
Innovation Solution
The implementation of a sawtooth configuration for grating couplers with a polysilicon material lined with SiN, integrated with a back end of line (BEOL) stack and a cladding layer to minimize reflections and enhance coupling efficiency, utilizing photolithographic processes for fabrication at the micrometer and nanometer scale.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-layer SiN top cladding is used for grating couplers, then the structure is simple and easy to manufacture, but the coupling efficiency is reduced due to additional reflection induced by the nitride cladding
Solution Approach 1:
The patent removes the problematic SiN top cladding layer from the grating coupler structure. By extracting this reflective layer, the design eliminates the source of additional reflections that reduce coupling efficiency, while maintaining manufacturing simplicity through the use of existing BEOL stack processes
Solution Approach 2:
The patent introduces an engineered BEOL stack with specific dielectric layers and metal reflections as an intermediary structure between the grating coupler and the external environment. This mediator controls light reflections through its layered composition, replacing the simple SiN cladding with a sophisticated but manufacturable stack that manages optical reflections without requiring additional cladding deposition
2Reliability
If grating couplers are designed with optimized configurations for high coupling efficiency, then light coupling improves, but the bandwidth remains limited due to the dispersive operating principle
Solution Approach 1:
The patent modifies key geometric parameters of the grating coupler including tooth height, tooth pitch, and sawtooth angle to optimize performance. By carefully tuning these parameters, the design achieves high coupling efficiency across a broader wavelength range, effectively expanding bandwidth while maintaining strong coupling through parameter optimization rather than structural complexity
3Reliability
If a polysilicon material with SiN liner and BEOL stack is integrated into the grating coupler, then coupling efficiency and tunability are enhanced, but the device complexity increases
Solution Approach 1:
The patent merges the grating coupler structure with the existing BEOL stack and polysilicon layers used in CMOS manufacturing. By combining these functional layers into a single integrated structure, the design achieves enhanced coupling efficiency and tunability without adding separate components, as the BEOL stack serves dual purposes of electrical interconnection and optical management
Solution Approach 2:
The patent designs the BEOL stack and polysilicon layers to serve multiple functions: electrical interconnection, optical reflection control, and structural support for the grating coupler. This multi-functionality allows the same layers to enhance coupling efficiency and provide tunability while avoiding the need for additional dedicated components, thereby managing complexity
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 configuration enhances light coupling and reflection into waveguide structures, achieving high-efficiency tunable grating couplers suitable for Si photonics and other photonics technologies, improving coupling efficiency and integrating seamlessly with CMOS technology.
Implementation Method 1
Grating couplers are commonly used in integrated optics for coupling light between integrated on-chip photonic waveguide structures and optical fibers. The grating couplers can couple light to and from the chip at any location
Implementation Method 2
Grating couplers with nitride top cladding suffer from limited coupling efficiency due to the additional reflection induced by the nitride cladding
Data Source
AI summary
The present disclosure relates to semiconductor structures and, more particularly, to grating couplers with multiple configurations and methods of manufacture. A structure includes: a grating coupler having a sawtooth configuration provided over a semiconductor slab; and a back end of line (BEOL) stack over the sawtooth configuration of the grating coupler.