Optical Semiconductor Chip RF Line Layout for Bandwidth Extension
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Solution Overview
Problem
Existing optical semiconductor chips face limitations in achieving higher speed and wider bandwidth due to the dominant influence of depletion layer capacitance in the optical waveguide, which restricts frequency response characteristics.
Innovation Solution
Incorporating a high frequency line between the electrode pad and the modulation electrode on the optical waveguide, providing inductance in series with the depletion layer capacitance, and embedding a low-dielectric-constant material or creating a hollow portion to reduce parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a direct modulation laser chip is formed with conventional electrode pad structure, then the chip can be manufactured with standard processes, but the frequency response characteristics deteriorate in high frequency range exceeding 10 GHz due to parasitic capacitance
Solution Approach 1:
The patent applies local quality by embedding a low dielectric constant material (such as air, vacuum, or low-k polymer) specifically in the region directly below the electrode pad, while leaving other regions with conventional insulation materials. This localized modification reduces parasitic capacitance at the critical electrode pad area without requiring complete restructuring of the entire device, thereby improving frequency response characteristics while maintaining manageable device complexity.
2Reliability
If the electrode pad size is reduced to minimize parasitic capacitance, then frequency response improves, but the area for signal input and connection becomes insufficient
Solution Approach 1:
The patent embeds low dielectric constant material specifically in the region directly below the electrode pad, which reduces parasitic capacitance without requiring reduction of the electrode pad's top surface area. This allows the electrode pad to maintain sufficient area for signal input and connection while achieving improved frequency response characteristics through the localized dielectric modification.
Solution Approach 2:
The low dielectric constant material acts as an intermediary between the electrode pad and the substrate, reducing the parasitic capacitance effect without requiring direct modification of the electrode pad's conductive structure or its connection interfaces. This intermediary approach allows the electrode pad to maintain its functional area while achieving capacitance reduction.
3Productivity
If a high frequency line providing inductance is added between the electrode pad and modulation electrode, then the inductance cancels the depletion layer capacitance effect and bandwidth increases, but the device structure becomes more complex
Solution Approach 1:
The patent merges the high frequency line function with the existing electrical connection structure between the electrode pad and modulation electrode. By integrating the inductance-providing trace into the existing signal path rather than adding a separate component, the patent achieves bandwidth extension through inductance-capacitance cancellation while minimizing the increase in device complexity.
Solution Approach 2:
The patent utilizes parameter changes by carefully designing the high frequency line's geometric parameters (length, width, trace pattern) to provide a specific inductance value that cancels the depletion layer capacitance effect at the target operating frequency. This parameter optimization allows bandwidth extension while keeping the structural addition minimal and manageable.
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 enhances the optical modulator's performance by improving frequency response characteristics, achieving higher speed and wider bandwidth.
Implementation Method 1
a high frequency line connecting the electrode pad and the modulation electrode and providing inductance in series with respect to a depletion layer capacitance of the optical waveguide
Implementation Method 2
A portion under the electrode pad 11 is embedded with a material 17 having a lower dielectric constant than that of the semiconductor insulation layer 13, and thereby the parasitic capacitance of the electrode pad 11 is reduced
Data Source
AI summary
An optical semiconductor chip of the present disclosure includes a high frequency line between an electrode pad receiving a modulation signal and a modulation electrode on the optical waveguide constituting a laser. The depletion layer capacitance generated in an active layer of the optical waveguide is cancelled by an inductance component of the high frequency line. When a portion directly below the high frequency line is embedded with a low-dielectric-constant material or is made hollow, the parasitic capacitance is further reduced. The high frequency line may have a zigzag shape as well as a linear shape. The electrode pad on the optical semiconductor chip can be connected to other substrates including RF lines for modulation signal input by bumps or wire bonding.