Optical Device Ground Wire Silicon Intermediary Impedance
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Solution Overview
Problem
The reduction in size of optical devices leads to longer metal wire connections, increasing the characteristic impedance and causing signal reflection due to impedance mismatch, which deteriorates the quality of the optical signal.
Innovation Solution
The implementation of silicon wires connected to the pads of both signal and ground wires, reducing the distance between the silicon wires and the signal wires, thereby reducing the characteristic impedance and minimizing signal reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the size of the optical device is reduced, then the integration density increases, but the distance between pads increases causing longer metal wires and higher characteristic impedance
Solution Approach 1:
Silicon wires are introduced as intermediary structures connecting to the ground wire end portion. These silicon wires act as mediators that provide additional grounding paths and reduce the characteristic impedance of the signal wire, thereby minimizing signal reflection without requiring changes to the overall device layout or pad positions
Solution Approach 2:
The ground wire structure is made non-uniform by adding silicon wires only at specific locations (end portions where signal reflection occurs). This local modification optimizes the grounding capability precisely where needed, rather than uniformly increasing ground wire cross-section throughout the entire device
2Ease of manufacture
If the distance between pad and optical device end portion is increased to allow laser dicing, then metal wire length increases causing impedance mismatch and signal reflection
Solution Approach 1:
Silicon wires serve as intermediary grounding elements that compensate for the increased metal wire length caused by larger pad-to-end-portion distances. By providing additional local grounding paths, they maintain signal integrity even when pads must be positioned farther from the optical device for laser dicing accessibility
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 suppresses the increase in characteristic impedance and reduces signal reflection, thereby improving the quality of the optical signal transmission.
Implementation Method 1
When the metal wire is long, the characteristic impedance of a wire increases. Reflection of an electric signal due to impedance mismatch occurs.
Implementation Method 2
Reflection of an electric signal due to impedance mismatch occurs. When the reflection of the electric signal occurs, the intensity of a signal having a part of frequencies corresponding to a reflected wave in a signal band fluctuates and the quality of the signal is deteriorated.
Data Source
AI summary
An optical transmission device includes a substrate, a waveguide, a signal wire, a ground wire, and a first stub wire. The waveguide is provided on the substrate and transmits an optical signal. The signal wire and the ground wire are disposed on the substrate along the waveguide and include, at end portions, bonding portions electrically connected to an external substrate by wires. The first stub wires are connected to the end portions of the ground wires. The distance between the signal wire and the first stub wire is shorter than the distance between the signal wire and the ground wire.