Dual DBR Reflection Layers for LED Thermal Protection

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Solution Overview

Problem

The traditional LED flip-chip technique faces challenges with heat dissipation and light efficiency due to the sapphire substrate's properties, and the selective laser lift-off process can damage LED dies, reducing yield and performance.

Innovation Solution

A light-emitting device with a first reflection layer to enhance external quantum efficiency and a second reflection layer to protect against laser-induced thermal damage during the selective LLO process, using distributed Bragg reflector layers to reflect light and laser wavelengths effectively.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a single reflection layer is used to enhance light emission, then external quantum efficiency is improved, but the LED dies become vulnerable to laser-induced thermal damage during selective LLO process

Engineering Contradiction:

Improveexternal quantum efficiencyVSAvoidlaser-induced thermal damage

Core Design Contradiction:

Use of energy by moving objectVSObject-affected harmful factors

Solution Approach 1:

The reflection layer is segmented into two distinct functional layers: a first reflection layer (DBR) optimized for reflecting LED emission wavelengths to enhance light extraction efficiency, and a second reflection layer optimized for reflecting laser wavelengths used in selective LLO to prevent thermal damage. This segmentation allows each layer to specialize in one function without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the reflection system are assigned different optical properties: the first reflection layer has high reflectivity at LED emission wavelengths (e.g., 450-530 nm) while the second reflection layer has high reflectivity at laser wavelengths (e.g., 355 nm). This local quality differentiation enables simultaneous optimization for both light emission and laser protection.

Inventive Principle:

Principle #3Local quality

2Ease of operation

If traditional pick-up head method is used for transferring LED chips, then individual chip placement is achieved, but the process becomes inefficient when die size is smaller than the pick-up head minimum size

Engineering Contradiction:

Improveindividual chip placement precisionVSAvoidtransfer efficiency

Core Design Contradiction:

Ease of operationVSProductivity

Solution Approach 1:

The mechanical pick-up head system is replaced with a selective laser lift-off system that uses optical fields (laser) to selectively release and transfer LED dies. This substitution enables handling of sub-100-micron dies that are too small for mechanical grippers, dramatically increasing productivity while maintaining precision through laser selectivity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The transfer mechanism transitions from mechanical contact-based pickup to laser-based selective release. By changing the physical parameter from mechanical force to optical energy, the system can handle much smaller die sizes and achieve higher throughput through parallel processing capabilities of laser arrays.

Inventive Principle:

Principle #35Parameter changes

3Stability of the object's composition

If sapphire substrate is used for LED growth, then lattice matching is achieved, but heat dissipation and static electricity problems occur

Engineering Contradiction:

Improvelattice matchingVSAvoidheat dissipation

Core Design Contradiction:

Stability of the object's compositionVSTemperature

Solution Approach 1:

The sapphire substrate is extracted and removed from the final LED structure after serving its purpose during epitaxial growth. The LED dies are transferred to a new substrate or mounting structure with superior thermal conductivity, eliminating the heat dissipation and electrostatic problems of sapphire while retaining the lattice-matching benefits achieved during the growth phase.

Inventive Principle:

Principle #2Taking out (Extraction)

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

Improves external quantum efficiency and increases the yield of LED dies by preventing thermal damage during the mass transfer process, enhancing both light emission and production efficiency.

Implementation Method 1

The first reflection layer is configured to reflect a waveband of light emitted from the LED dies

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

The second reflection layer is configured to reflect a laser waveband, wherein the wavelength of the laser waveband is less than 420 nm

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 3

using distributed Bragg reflector layers to reflect light and laser wavelengths effectively

Methodology Applied

Scientific EffectBragg Diffraction: Bragg Diffraction

Data Source

PatentUS20230197905A1Light-emitting device and forming method thereof

Publication Date: 2023.06.22 ENNOSTAR CORP

AI summary

A light-emitting device includes a substrate, a plurality of light-emitting diode (LED) dies, a first reflection layer, and a second reflection layer. The LED dies are on the substrate. The first reflection layer is on the LED dies. The second reflection layer is on the first reflection layer. The first reflection layer is configured to reflect a waveband of light emitted from the LED dies. The second reflection layer is configured to reflect a laser waveband, wherein the wavelength of the laser waveband is less than 420 nm.