Transparent Conductive Spacer Layer for Laser Lift-Off LED Arrays

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Solution Overview

Problem

The existing methods for manufacturing monolithic LED arrays face challenges during the laser lift-off process, as metal side-contacts interact with the laser beam, leading to metal-rich droplets, reduced light output, and potential electrical instability and reliability issues.

Innovation Solution

The implementation of a transparent conductive layer with a bandgap close to that of the epitaxial layer, such as zinc oxide, is used to absorb the laser beam during the lift-off process, protecting the metallic layers and preventing interaction, thereby enhancing light output and electrical performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If metal side-contacts are used as cathode contacts during laser lift-off process, then electrical cathode function is achieved, but metal-rich droplets are formed and light output is reduced

Engineering Contradiction:

Improveelectrical cathode functionVSAvoidmetal-rich droplets

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

A transparent conductive oxide layer (such as ITO, ZnO, or Al-doped ZnO) is introduced as an intermediary layer between the metal cathode contact and the laser beam during the lift-off process. This intermediate layer absorbs the laser energy and prevents direct interaction between the laser and metal layers, eliminating metal-rich droplet formation while maintaining electrical conductivity and cathode function.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent converts the potentially harmful laser-metal interaction into a beneficial process by using the transparent conductive oxide layer to absorb laser energy. The layer that could be considered a barrier actually protects the metal layers from laser damage, transforming the laser lift-off process from harmful to beneficial by preventing droplet formation and improving light output.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Reliability

If metal side-contacts are used as cathode contacts, then electrical conductivity is provided, but electrical instability and leakage occur

Engineering Contradiction:

Improveelectrical stabilityVSAvoidelectrical leakage

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The transparent conductive oxide layer serves as a protective intermediary between the metal cathode contact and the semiconductor structure. This intermediate layer provides electrical conductivity while preventing direct contact between metal and semiconductor, thereby eliminating electrical leakage paths and stabilizing the cathode's electrical performance.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Illumination intensity

If substrate is removed by laser lift-off process, then light extraction is enhanced, but metal layers interact with laser beam

Engineering Contradiction:

Improvelight extractionVSAvoidlaser-metal interaction

Core Design Contradiction:

Illumination intensityVSObject-generated harmful factors

Solution Approach 1:

The transparent conductive oxide layer acts as a mediator that allows the laser beam to pass through during lift-off while protecting the metal layers from direct laser interaction. The layer is transparent to the laser wavelength used, enabling substrate removal and light extraction enhancement without causing metal droplet formation or other harmful laser-metal interactions.

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

This approach results in improved light output, electrical performance, and increased reliability of the LED arrays by preventing laser interaction with metallic layers, ensuring uniform and reproducible fabrication processes.

Implementation Method 1

a transparent conductive layer with a bandgap close to that of the epitaxial layer, such as zinc oxide, is used to absorb the laser beam during the lift-off process

Methodology Applied

Scientific EffectLaser absorption: Absorption (EM radiation)

Data Source

PatentUS20230155066A1Composite cathode contact with spacer layer for monolithically integrated micro-leds, mini-leds, and LED arrays

Publication Date: 2023.05.18 LUMILEDS SINGAPORE PTE LTD

AI summary

An LED device comprises a mesa comprising semiconductor layers, the semiconductor layers including an N-type layer, an active layer, and a P-type layer, the mesa having a top surface and at least one side wall, the at least one side wall defining a trench have a bottom surface. A transparent conductive layer is on at least one side wall and in the trench. A cathode layer is in the trench on the transparent conductive layer. A p-type contact is on the top surface of the mesa. In some embodiments, a spacer layer is formed between the transparent conductive layer and the cathode layer. In other embodiments, a distributed Bragg reflector is formed between the transparent conductive layer and the cathode layer.