Optical Semiconductor Pad Layout for Low Parasitic Capacitance

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Solution Overview

Problem

Optical semiconductor devices face challenges in reducing parasitic capacitance and maintaining high-speed operation due to issues with impurity diffusion and electrode design, particularly in buried hetero structures, which can lead to increased capacitance and optical interference.

Innovation Solution

The device incorporates a high resistance region in the semiconductor layer that electrically isolates electrode regions, avoiding the optical functional layer and minimizing parasitic capacitance by using impurity diffusion or re-growth methods to create distinct electrical domains.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If impurities are diffused from the upper surface of the semiconductor multilayer to reduce parasitic capacitance, then the parasitic capacitance of the electrode pad is reduced, but the controllability of the diffusion process decreases and impurities cannot be arranged in the desired region

Engineering Contradiction:

Improveparasitic capacitanceVSAvoidcontrollability of diffusion process

Core Design Contradiction:

Loss of energyVSManufacturing precision

Solution Approach 1:

A groove is formed in the semiconductor multilayer structure before the impurity diffusion process. This preliminary structural preparation guides the diffusion of impurities into the groove, ensuring they reach the semi-insulating substrate while maintaining precise spatial control. The groove acts as a pre-defined pathway that solves both the parasitic capacitance reduction need and the diffusion control requirement

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The groove serves as an intermediary structure between the electrode pad and the semi-insulating substrate. It provides a controlled channel for impurity diffusion, mediating between the need to reduce parasitic capacitance (by reaching the substrate) and the need for manufacturing precision (by controlling where impurities go). The groove geometry controls the diffusion process outcome

Inventive Principle:

Principle #24Intermediary (Mediator)

2Loss of energy

If the diffusion region is arranged next to the optical functional layer to reduce parasitic capacitance, then the parasitic capacitance is reduced, but optical influence such as increased light absorption occurs

Engineering Contradiction:

Improveparasitic capacitanceVSAvoidoptical influence

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

The groove is designed with specific local geometric properties (depth, width, shape) that are optimized to allow impurity diffusion to the substrate while maintaining a controlled distance from the optical functional layer. This local structural quality ensures that the diffusion region achieves low parasitic capacitance without causing harmful optical effects, creating different functional zones with appropriate properties

Inventive Principle:

Principle #3Local quality

3Loss of energy

If a groove is used to surround the electrode pad to reduce parasitic capacitance, then the parasitic capacitance is reduced, but the wiring length from the electrode pad to the mesa structure is increased

Engineering Contradiction:

Improveparasitic capacitanceVSAvoidwiring length

Core Design Contradiction:

Loss of energyVSLength of moving object

Solution Approach 1:

Instead of forming a complete surrounding groove around the entire electrode pad, the groove is formed only in the necessary regions to achieve parasitic capacitance reduction. This partial action approach reduces parasitic capacitance where it matters most (near the pad edges) while avoiding the excessive wiring length increase that would result from a complete surrounding groove structure

Inventive Principle:

Principle #16Partial or excessive action

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 design effectively reduces parasitic capacitance, enhancing high-speed operation by minimizing electrical interference and maintaining the integrity of the optical functional layer.

Implementation Method 1

a diffusion region is formed, in which p-type or insulating impurities are diffused from an upper surface of the semiconductor multilayer to the semi-insulating substrate

Methodology Applied

Scientific EffectImpurity diffusion: Diffusion

Data Source

PatentUS20250306406A1Optical semiconductor device

Publication Date: 2025.10.02 WELLS FARGO BANK NA

AI summary

Provided is an optical semiconductor device that has an excellent characteristic. The optical semiconductor device includes: first and second conductivity type semiconductor layers; an optical functional layer; a first electrode including a first pad electrode, the first electrode being connected to the first conductivity type semiconductor layer; and a second electrode including a second pad electrode configured to receive an electric signal as input, the second electrode being connected to the second conductivity type semiconductor layer. The first conductivity type semiconductor layer includes first and second regions, and a high resistance region overlapping the second region. The first region overlaps, an entire region of the first pad electrode. The second region overlaps, an entire region of the second pad electrode. The high resistance region is arranged to avoid the optical functional layer. The high resistance region has an outer edge which divides the first region and the second region.