Curved Reflective Layer in Flip-Chip Light-Emitting Devices

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Solution Overview

Problem

Conventional flip-chip light-emitting devices face challenges with low cohesive force between the p-type nitride semiconductor layer and the reflective layer, leading to unstable contact resistance and low reflection efficiency, which affects light extraction and heat emission efficiency.

Innovation Solution

A light-emitting device with a reflective layer formed on a transparent electrode layer having a curved surface, where the reflective layer is deposited on the transparent electrode layer with a curved surface to enhance light reflection and heat emission, using materials like Al and employing techniques such as wet etching and spherical particle arrangement to create the curved surface.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If Ag is used as the reflective layer material, then reflection efficiency is improved, but cohesive force with the p-type nitride semiconductor layer becomes very low

Engineering Contradiction:

Improvereflection efficiencyVSAvoidcohesive force

Core Design Contradiction:

Illumination intensityVSStrength

Solution Approach 1:

The patent uses a composite reflective layer structure consisting of Ag and Al materials. The Ag layer provides high reflection efficiency while the Al layer provides strong cohesive force with the p-type nitride semiconductor layer. This composite structure resolves the contradiction by combining the advantages of both materials to achieve both high reflection efficiency and strong adhesion.

Inventive Principle:

Principle #40Composite materials

2Strength

If Al is used as the reflective layer material, then cohesive force is improved, but reflection efficiency becomes relatively low compared to Ag

Engineering Contradiction:

Improvecohesive forceVSAvoidreflection efficiency

Core Design Contradiction:

StrengthVSIllumination intensity

Solution Approach 1:

Inventive Principle:

Principle #40Composite materials

3Ease of manufacture

If a flat reflective layer is used, then manufacturing is simpler, but light extraction efficiency is reduced

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidlight extraction efficiency

Core Design Contradiction:

Ease of manufactureVSIllumination intensity

Solution Approach 1:

The patent forms the reflective layer on a curved surface of the transparent electrode layer instead of a flat surface. The curved surface structure improves light extraction efficiency by enabling light to be reflected in a vertical direction, while the curvature is formed through standard manufacturing processes such as wet etching, maintaining ease of manufacture.

Inventive Principle:

Principle #14Spheroidality (Curvature)

4Device complexity

If the reflective layer is formed directly on the p-type nitride semiconductor layer, then manufacturing steps are reduced, but contact resistance becomes unstable

Engineering Contradiction:

Improvenumber of manufacturing stepsVSAvoidcontact resistance stability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent introduces a transparent electrode layer as an intermediary between the p-type nitride semiconductor layer and the reflective layer. This transparent electrode layer serves as a buffer that ensures stable electrical contact and low contact resistance, while also providing a suitable surface for forming the reflective layer. The intermediary layer resolves the contradiction by providing both electrical stability and manufacturing feasibility.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 solution improves light extraction efficiency by reflecting light in a vertical direction and enhances heat emission efficiency through the use of a high heat conductivity reflective layer, addressing the issues of low cohesive force and reflection efficiency in conventional devices.

Implementation Method 1

a reflective layer formed on the transparent electrode layer in such a fashion that the curved surface formed on the transparent electrode layer is transferred so as to reflect the light generated from the light-emitting layer toward the light-emitting layer

Methodology Applied

Scientific EffectLight reflection: Reflection

Implementation Method 2

forming a reflective layer on the transparent electrode layer in such a fashion that the curved surface formed on the transparent electrode layer is transferred

Methodology Applied

Scientific EffectPhysical vapor deposition: Physical Vapour Deposition

Implementation Method 3

reflect the light generated from the light-emitting layer toward the light-emitting layer

Methodology Applied

Scientific EffectOptical directionality: Reflection

Implementation Method 4

enhances heat emission efficiency through the use of a high heat conductivity reflective layer

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentUS8674594B2Flip-chip type light-emitting device with curved reflective layer

Publication Date: 2014.03.18 KOREA UNIV IND & ACADEMIC CALLABORATION FOUND

AI summary

A light-emitting device comprises a substrate; a light-emitting layer formed on the substrate; a transparent electrode layer formed on the light-emitting layer, the transparent electrode layer having a curved surface; and a reflective layer formed on and along the curved surface of the transparent electrode layer such that the curved surface of the transparent electrode layer is transferred so as to reflect the light generated from the light-emitting layer toward the light-emitting layer.