Embedded RF Shield Layout for Silicon Optical Modulator Crosstalk
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Solution Overview
Problem
High-speed silicon photonics face undesired absorption loss and RF crosstalk due to electromagnetic fields from RF signals extending into partially conducting silicon substrates, which is exacerbated by the limitations of using high-resistivity substrates that restrict wafer availability and degrade long-range RF crosstalk performance.
Innovation Solution
A metal shield is placed between the optical modulator and the silicon substrate to block electromagnetic fields, allowing the use of low resistivity substrates while reducing RF absorption loss and crosstalk, with the shield being either a solid layer or patterned into discrete bars to optimize modulator characteristics and minimize additional RF loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If high-resistivity silicon substrates are used to reduce RF absorption loss, then RF absorption loss is reduced, but wafer availability is restricted and long-range RF crosstalk performance is degraded
Solution Approach 1:
A metal shield layer is introduced as an intermediary component between the optical modulator and the silicon substrate. This shield acts as a mediator that blocks electromagnetic fields from penetrating into the substrate, thereby reducing RF absorption loss while allowing the use of low-resistivity substrates that offer better wafer availability and long-range crosstalk performance
2Loss of energy
If high-resistivity silicon substrates are used to reduce RF absorption loss, then RF absorption loss is reduced, but long-range RF crosstalk performance is degraded
Solution Approach 1:
The metal shield serves as a protective intermediary that selectively blocks harmful electromagnetic fields from reaching the substrate, reducing RF absorption loss while preserving long-range RF crosstalk performance by allowing the use of low-resistivity substrates
3Loss of energy
If metal shield is added to block electromagnetic fields, then RF absorption loss is reduced, but device complexity increases
Solution Approach 1:
The shield's geometric parameters (pattern, size, spacing) are optimized to achieve effective electromagnetic field blocking with minimal additional structure. By carefully controlling the shield's physical parameters, the patent reduces RF absorption loss while keeping the added complexity manageable
Solution Approach 2:
The metal shield can be implemented as discrete patterned bars or segments rather than a continuous layer, which reduces the amount of material required and simplifies fabrication while maintaining effective field blocking performance
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
The metal shield effectively suppresses long-range RF crosstalk by more than 10 decibels compared to high-resistivity substrates, enabling the use of low resistivity substrates without degrading modulator performance and reducing RF absorption loss across a wide range of substrate resistivities.
Implementation Method 1
a metal shield formed in the dielectric material between the optical modulator and the silicon substrate, the metal shield blocking an electromagnetic field of a driving signal of the optical modulator from extending into the silicon substrate
Data Source
Figure 1
Figure 2A
Figure 2B~2C
AI summary
A device and a method of fabricating the device are provided. The device includes an optical modulator formed in a dielectric material, a silicon substrate adjacent the dielectric material, and a metal shield formed in the dielectric material between the optical modulator and the silicon substrate. The metal shield blocks an electromagnetic field of a driving signal of the optical modulator from extending into the silicon substrate.