Substrate-Coupled Grating Couplers for Shorter PIC-to-PCB Contacts
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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 bond wires due to the substrate thickness, as conventional grating couplers require wirebonds that exceed the PIC thickness, limiting the frequency response.
Innovation Solution
A flip-chip arrangement is used where the PIC is oriented with the wafer side facing the PCB, allowing for shorter electrical contacts and a novel grating coupler design that redirects light paths through the substrate, using waveguide, cladding, or insulator side grating features to minimize contact length and inductance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the PIC is placed substrate side down on the PCB with conventional grating couplers, then the structural integrity is maintained, but the wirebond length increases and frequency response is limited
Solution Approach 1:
The patent inverts the conventional mounting orientation by placing the PIC wafer side down on the PCB instead of substrate side down. This inversion allows the grating coupler to be positioned on the substrate side, enabling wirebonds to connect to contact pads on the same side as the grating coupler, thereby reducing wirebond length and improving frequency response while maintaining structural integrity through the substrate.
2Reliability
If the wirebonds extend to the PCB from the opposite side of the PIC, then electrical contact is established, but the contact length increases and inductance increases
Solution Approach 1:
The patent changes the spatial dimension of electrical contact by moving the contact pads from the wafer side to the substrate side, where they are positioned adjacent to the grating coupler. This dimensional repositioning allows wirebonds to make electrical contact much closer to the grating coupler, significantly reducing wirebond length and associated inductance while maintaining reliable electrical connection.
3Speed
If the minimum total thickness of the PIC is reduced, then the wirebond length decreases and frequency response improves, but the substrate may lose structural integrity
Solution Approach 1:
The patent extracts the grating coupler function from the wafer side and positions it on the substrate side, allowing the substrate to serve dual purposes: maintaining structural integrity and providing a platform for the grating coupler. This extraction enables the substrate to support the grating coupler structures while wirebonds connect to contact pads on the same side, reducing wirebond length without compromising substrate strength.
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 enables faster frequency response by reducing contact inductance and optimizing signal communication between PICs and PCBs, enhancing communication efficiency.
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
Implementation Method 2
A reflector is disposed over the grating coupler to reflect light emitted from the grating coupler through the substrate
Implementation Method 3
A reflector is disposed over the grating coupler to reflect light emitted from the grating coupler through the substrate to emit from the backside of the PIC chip or to reflect light collected from the backside of the PIC chip through the substrate and to the grating coupler
Data Source
Figure 1A
Figure 1B~1C
Figure 1D~1E
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.