Surface-Normal Optoelectronic Coupler for Inter-Chip Optical Communication
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Solution Overview
Problem
Current multi-chip module (MCM) technologies face challenges in achieving reliable, low-power, and low-bit error rate off-chip communication due to stringent alignment requirements and high costs associated with silicon-on-insulator (SOI) process technology, particularly in photonically interconnecting silicon chips for optical proximity communication (OPxC).
Innovation Solution
The MCM design incorporates substrates with optical waveguides and surface-normal optoelectronic devices, such as quantum-well devices, which redirect optical signals perpendicular to the surface, allowing for selective inter-chip communication without the need for precise lateral alignment and reducing the reliance on expensive SOI process technology by using standard CMOS chips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If grating-coupler based OPxC, reflecting-mirror based OPxC, or OPxC using ball lenses in etch pits is used, then optical signal transmission between chips is achieved, but very accurate vertical and lateral alignment is required
Solution Approach 1:
The patent transitions from lateral coupling (in-plane) to vertical coupling (out-of-plane) by using upward-facing waveguides on the first chip and downward-facing waveguides on the second chip. This dimensional change from lateral to vertical orientation eliminates the need for precise lateral alignment while maintaining optical coupling efficiency through the gap between chips.
Solution Approach 2:
The patent introduces an intermediary optical coupling mechanism through the use of vertically oriented waveguides that extend through the chip thickness. These waveguides act as intermediaries that guide optical signals from the input chip through the gap to the output chip, replacing the need for direct lateral alignment between facing surfaces.
2Reliability
If etch-pit and ball-lens techniques are used to provide accurate alignment, then reliable OPxC is achieved, but thermal expansion remains a concern
Solution Approach 1:
By orienting waveguides vertically rather than laterally, the patent reduces sensitivity to thermal expansion in the lateral direction. The vertical coupling geometry means that lateral thermal expansion of the chips does not significantly affect the optical coupling, as the coupling occurs through the gap in the vertical dimension rather than across laterally expanding surfaces.
3Reliability
If bridge chips are fabricated using silicon-on-insulator (SOI) process technology to accommodate waveguide-based optical modulators and photo-detectors, then optical communication functionality is achieved, but the cost of bridge chips increases
Solution Approach 1:
The patent divides the MCM into functional segments: routing chips that use standard CMOS with lateral waveguides for signal routing, and bridge chips that can use alternative processes for optoelectronic devices. This segmentation allows each type of chip to be optimized for its specific function while using the most cost-effective manufacturing process appropriate for that function.
Solution Approach 2:
The patent enables bridge chips to perform multiple functions (optical transmission, reception, and routing) using devices fabricated on silicon substrates without requiring full SOI process technology. The upward-facing and downward-facing waveguide configurations allow standard CMOS chips to function as effective bridge chips, reducing manufacturing costs while maintaining optical communication capability.
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 relaxes alignment tolerances, reduces costs, and facilitates efficient optical signal transmission between chips, enabling reliable and cost-effective inter-chip communication while maintaining low power consumption and bit error rates.
Implementation Method 1
an optical coupler, optically coupled to the first optical waveguide, which redirects an optical signal to and/or from the first optical waveguide and a direction normal to the first surface
Implementation Method 2
communication of optical signals (such as 'optical proximity communication' or OPxC)
Data Source
AI summary
A multi-chip module (MCM) is described. This MCM includes two substrates having facing surfaces. Disposed on a surface of a first of these substrates, there is an optical waveguide, having an eigenmode in the plane of the surface, and an optical coupler, which redirects optical signals to and/or from the optical waveguide and a direction normal to the surface. Furthermore, disposed on a surface of a second of the substrates, which faces the surface of the first substrate, and which overlaps the optical coupler, there is an optoelectronic device. This optoelectronic device, which has an eigenmode in a direction perpendicular to the surface of the second substrate, selectively receives or provides the optical signal to and/or from the optical coupler. For example, the selective receiving or providing may be controlled by selectively applying a potential to the quantum-well device, thereby changing the optical properties of the optoelectronic device.