Composite Cathode Contact Layout for Laser Lift-Off LED Arrays

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Solution Overview

Problem

The interaction of metallic layers with laser beams during the laser lift-off process in monolithic LED arrays leads to metal-rich droplets and impaired sidewall contacts, affecting light output and electrical performance, posing reliability concerns.

Innovation Solution

Incorporating an optically transparent and electrically conductive layer, such as zinc oxide, at the bottom of the epitaxial structure to absorb laser beams and protect metallic layers during substrate removal, thereby preventing interaction and ensuring uniformity and improved electrical performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If laser lift-off process is used to remove substrate, then substrate removal is achieved, but metallic layers interact with laser beam creating metal-rich droplets and impairing sidewall contacts

Engineering Contradiction:

Improvesidewall contact qualityVSAvoidlaser-metal interaction effects

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

A sacrificial layer is introduced as an intermediary between the laser beam and the metallic cathode contact layers. This sacrificial layer absorbs the laser energy and prevents direct interaction between the laser and the metallic layers, thereby eliminating metal-rich droplet formation and sidewall contact impairment while still enabling substrate removal through laser lift-off.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The harmful interaction between laser and metallic layers is converted into a beneficial process by using the laser energy to selectively remove a sacrificial layer that has been specifically designed to absorb laser energy. This converts the potentially damaging laser-metal interaction into a controlled material removal process that protects the cathode contacts.

Inventive Principle:

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

2Reliability

If cathodes are entrenched down to substrate surface, then electrical contact is improved, but laser interaction creates metal-rich droplets that decrease light output

Engineering Contradiction:

Improveelectrical contact stabilityVSAvoidlight output

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The sacrificial layer serves as a protective intermediary that prevents laser energy from reaching the entrenched cathode layers. This allows the cathodes to maintain their entrenched configuration for reliable electrical contact while the sacrificial layer absorbs the laser energy that would otherwise create light-absorbing metal droplets.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If standard laser lift-off is used, then substrate removal is achieved, but metal-containing by-products are created that affect long-term reliability

Engineering Contradiction:

Improvesubstrate removal processVSAvoidlong-term device reliability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The laser energy that would create harmful metal by-products is instead directed at the sacrificial layer, converting a potentially damaging interaction into a beneficial material removal process. The sacrificial layer is designed to be completely removed or transformed, leaving no harmful metal-containing residues that would compromise long-term reliability.

Inventive Principle:

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

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

Enhances light output, improves electrical performance, and increases reliability by preventing laser interaction with metallic layers, resulting in more uniform and reproducible fabrication processes for monolithic LED arrays.

Implementation Method 1

Incorporating an optically transparent and electrically conductive layer, such as zinc oxide, at the bottom of the epitaxial structure to absorb laser beams

Methodology Applied

Scientific EffectAbsorption (EM radiation): Absorption (EM radiation)

Data Source

PatentUS12588326B2Composite cathode contact for monolithically integrated micro-LEDs, mini-LEDs and LED arrays

Publication Date: 2026.03.24 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.