Substrate-Coupled Grating Couplers for Shorter PIC-to-PCB Links
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Solution Overview
Problem
The frequency response of communication between photonic integrated circuits (PICs) and electrical printed circuit boards (PCBs) is limited by the length of wirebonds, which exceeds the thickness of the PIC chip due to the conventional substrate-side-down mounting, restricting the miniaturization and efficiency of signal conversion.
Innovation Solution
A PIC chip is mounted to a PCB with the wafer side facing the PCB, featuring a grating coupler with taper and grating features extending toward the substrate, allowing for shorter electrical contacts and improved frequency response by redirecting optical signals through the waveguide layer and substrate, enabling the use of two distinct grating layers and insulator layers for efficient signal transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the PIC is mounted substrate side down on the PCB with conventional wirebonding, then the chip provides sufficient structural integrity through the substrate layer, but the wirebond length exceeds the chip thickness and limits frequency response
Solution Approach 1:
The patent inverts the conventional mounting orientation by placing the wafer side (containing the grating coupler) facing the PCB instead of the substrate side. This inversion allows electrical contacts to be made at the wafer level rather than requiring wirebonds to span the entire chip thickness, thereby reducing contact length and improving frequency response while maintaining structural integrity through the substrate.
2Ease of manufacture
If wirebonds extend from the opposite side of the PIC to the PCB, then electrical connection is established, but the bond wire length must exceed the thickness of the entire PIC including substrate
Solution Approach 1:
By inverting the mounting orientation so the wafer side faces the PCB, the patent enables electrical contacts to be established at the wafer level where the grating coupler is located. This eliminates the need for wirebonds to span the entire chip thickness, significantly reducing bond wire length while maintaining ease of manufacturing through standard bonding processes.
Solution Approach 2:
The patent transitions from three-dimensional wirebonding through the chip thickness to a more planar contact arrangement at the wafer level. By utilizing the wafer surface dimension rather than penetrating through the substrate thickness, the solution reduces the effective path length for electrical connections.
3Productivity
If the grating features extend toward the substrate from the taper portion, then optical signals are redirected through the waveguide layer, but the mounting orientation must be changed to wafer side down
Solution Approach 1:
The patent inverts the conventional mounting orientation to place the wafer side with the grating coupler facing the PCB. This orientation change enables the grating features to effectively redirect optical signals through the waveguide layer while simultaneously allowing short electrical contacts to reach the PCB, thereby improving signal transmission efficiency without compromising ease of operation.
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 reduces the length of electrical contacts, lowering inductance and enhancing the frequency response, allowing for faster communication between the PIC and PCB while maintaining structural integrity and optical signal redirection.
Implementation Method 1
Grating in the form of uneven features on a side of the taper portion facing a cladding layer of the chip direct a photonic signal either into or out of the plane of the taper portion
Data Source
AI summary
A photonic integrated circuit chip includes a substrate and a wafer on the substrate. The wafer itself includes a photonic grating coupler with a taper portion and grating features. The grating features extend from the taper portion toward the substrate.