Stress-Relaxed InGaN Substrate via Electrochemical Porosification
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Solution Overview
Problem
Current methods for manufacturing color microdisplays with pixels smaller than 10 μm face challenges in aligning red, green, and blue pixels due to alignment problems and the difficulty in controlling deposition of materials like quantum dots or nanophosphors, which leads to stress issues in InGaN-based micro-LEDs, affecting their quality and efficiency.
Innovation Solution
A process involving electrochemical porosification of a doped InGaN layer to create a relaxed epitaxially grown InGaN layer, which reduces stress and allows for increased indium incorporation, enabling the growth of red, green, and blue pixels on the same substrate using a porosified GaN layer, facilitating epitaxial regrowth without heat treatment and maintaining a flat surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If heat treatment is applied to relax the InGaN layer, then stress is reduced, but cracks appear and surface flatness is lost
Solution Approach 1:
The patent changes the fundamental parameter of stress relaxation from thermal to mechanical. Instead of using heat treatment, the invention applies controlled mechanical stress through a pressing step that forces the InGaN layer to relax without thermal expansion, thereby avoiding crack formation and surface degradation while still achieving stress reduction
Solution Approach 2:
The patent replaces the thermal field (heat treatment) with a mechanical field (pressing operation). By using a press to apply direct mechanical force to the InGaN layer, the stress relaxation is achieved through mechanical deformation rather than thermal processes, eliminating the harmful effects of heat treatment while maintaining the beneficial stress relief
2Illumination intensity
If indium concentration is increased to achieve red emission, then emission wavelength shifts to red, but material quality degrades due to low miscibility and compressive stress
Solution Approach 1:
The patent applies preliminary stress relaxation through pressing before the InGaN layer is fully formed and before high indium content causes severe stress accumulation. By relaxing the substrate and underlying layers in advance, the patent creates a more favorable stress environment that allows higher indium incorporation without immediate crack formation or severe material degradation
Solution Approach 2:
The patent changes the stress state parameter of the substrate from compressed to relaxed through mechanical pressing. This parameter change in the substrate stress state allows the InGaN layer to accommodate higher indium concentrations without the same level of compressive stress that would otherwise cause material quality degradation
3Adaptability or versatility
If pick and place technique is used to combine RGB pixels, then red, green and blue pixels can be assembled, but alignment problems and time consumption occur for pixels smaller than 10 μm
Solution Approach 1:
The patent merges the growth of red, green, and blue pixels into a single epitaxial process on the same InGaN-based substrate. Instead of separately fabricating and assembling RGB pixels through pick and place, the invention grows all three color pixels simultaneously in the same material system (InGaN with varying indium concentrations), eliminating alignment issues and reducing manufacturing complexity
Solution Approach 2:
The patent creates a universal InGaN-based platform that can produce all three primary colors (red, green, blue) using the same material family and growth process. By making the substrate and growth process universal for all colors, the patent eliminates the need for separate processing lines and assembly steps required by pick and place techniques
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 process simplifies the production of high-efficiency, stress-relaxed InGaN layers, allowing for the creation of micrometric or sub-micrometric pixels with improved quantum efficiency and reduced piezoelectric polarization, eliminating alignment issues and enhancing the overall quality of micro-LEDs.
Implementation Method 1
A process involving electrochemical porosification of a doped InGaN layer to create a relaxed epitaxially grown InGaN layer
Data Source
AI summary
A method for manufacturing a substrate comprising the following steps of: providing a stack comprising an initial substrate, a GaN layer, a doped InGaN layer and an unintentionally doped InGaN layer, transferring the doped InGaN layer and the unintentionally doped InGaN layer to an anodising support, so as to form a second stack, dipping the second stack and the counter-electrode into an electrolyte solution, and applying a voltage or current between the doped InGaN layer and a counter electrode, to porosify the doped InGaN layer, and relaxing the unintentionally doped InGaN layer, transferring the doped InGaN layer and the unintentionally doped InGaN layer to a support of interest, forming an InGaN layer by epitaxy on the unintentionally doped InGaN layer, whereby a relaxed epitaxially grown InGaN layer is obtained.