Erasable Ion-Implanted Optical Coupler for Wafer Testing
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Solution Overview
Problem
Current photonic integrated circuits (PICs) face high failure rates and increased costs due to limited wafer-scale testing capabilities, as conventional directional couplers are permanent and cause signal loss, restricting the number of testing points and optical power available.
Innovation Solution
The development of erasable ion-implanted optical couplers that can be spatially efficiently fabricated and removed after testing, allowing for minimal signal loss and enabling early detection of defective chips without permanent modification to the PIC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional directional couplers are used for wafer-scale testing, then testing capability is provided, but signal loss occurs and the number of testing points is limited
Solution Approach 1:
The patent applies the dynamics principle by making the coupler erasable rather than permanent. The coupler can be dynamically created when needed for testing and then erased/removed afterward. This is achieved through ion implantation that can be reversed by thermal annealing, allowing the coupler structure to transition between coupled and uncoupled states, thereby eliminating permanent signal loss while maintaining testing capability.
Solution Approach 2:
The patent utilizes parameter changes by modifying the refractive index of the waveguide material through ion implantation to create the coupler, and then reversing this parameter change through thermal annealing to erase the coupler. The ion implantation alters the physical and chemical properties of the silicon material, changing its refractive index to enable coupling, and subsequent annealing restores the original properties, allowing the coupler to be removed without permanent signal loss.
2Reliability
If conventional directional couplers are permanently fabricated, then testing is enabled, but real estate on the PIC is consumed and optical power is limited
Solution Approach 1:
The erasable coupler allows the same physical space to be reused for multiple testing operations. After testing is complete, the coupler is erased and the space becomes available for other purposes or additional testing points. This dynamic creation and removal capability significantly increases the effective number of testing points that can be implemented on a given PIC without permanently consuming waveguide real estate.
Solution Approach 2:
The patent implements discarding and recovering by temporarily creating the coupler structure for testing purposes, using it to extract optical power for measurement, and then erasing/removing the coupler afterward. The waveguide real estate and optical power are recovered for normal circuit operation or additional testing, maximizing the utilization of limited PIC resources.
3Adaptability or versatility
If ion implantation is used to create erasable couplers, then couplers can be removed after testing, but additional processing steps are required
Solution Approach 1:
The patent merges the coupler creation and erasure processes into a single ion implantation followed by thermal annealing sequence. The ion implantation step creates the coupler, and the subsequent annealing step erases it. By combining these functions into a integrated fabrication flow that leverages existing semiconductor processing capabilities, the added complexity is minimized while achieving the erasable functionality.
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 solution reduces processing wastage and fabrication costs by allowing for effective wafer-scale autonomous testing, maintaining high coupling efficiency and preserving photonic circuit real estate, while enabling the identification of defective components during fabrication.
Implementation Method 1
an ion-implanted waveguide optical coupler which couples light between waveguides
Implementation Method 2
adjacent to and spaced apart from the conventional waveguide, such that evanescent coupling of light
Implementation Method 3
The annealing process may be a whole wafer process across the photonic circuit wafer, or a localised process
Data Source
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AI summary
The disclosure provides a method of forming an erasable optical coupler in a photonic device comprising a conventional optical waveguide formed in a crystalline wafer. The method comprises selectively implanting ions in a localised region of the wafer material adjacent to the conventional waveguide of the photonic device, to cause modification of the crystal lattice structure of, and a change in refractive index in, the ion implanted region of the wafer material to thereby form an ion implanted waveguide optically coupled to the adjacent conventional waveguide to couple light out therefrom, or in thereto. The crystalline wafer material and ion implanted waveguide are such that the crystal lattice structure or composition can be modified to adjust or remove the optical coupling with the conventional waveguide by further modification of the refractive index in the ion implanted region, in particular by heating. The disclosure also includes an apparatus for carrying out the method, devices fabricated by means of the method, an apparatus for testing an erasable coupler in a waveguide device, and an apparatus for erasing an optical coupler comprising means for localised annealing of a material of the waveguide device, in particular by means of heat or light, as well as a system for sequentially producing a photonic device comprising the fabrication, testing and erasing apparatuses.