Native Emission RGB Matrix Using Relaxed InGaN Mesa Structures
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Solution Overview
Problem
Current methods for manufacturing color microdisplays with pixels smaller than 10 µm face challenges in aligning blue, green, and red pixels due to alignment problems and time constraints, and struggle with the deposition and robustness of quantum dots or nanophosphors, necessitating the use of a single family of materials like InGaN for native emission.
Innovation Solution
A method involving a patterned substrate with mesas of different relaxation rates for selective porosification and epitaxy, allowing for the growth of LEDs with varying indium concentrations to achieve blue, red, and green emissions, using a basic structure with GaN, In(x)GaN doped layers, and non-intentionally doped In(x)GaN epitaxy recovery layers, enabling the formation of a native emission RGB matrix.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the pick and place technique is used to combine blue, green, and red pixels on the same substrate, then color microdisplays can be manufactured, but alignment problems and time constraints occur for pixels smaller than 10 μm
Solution Approach 1:
The patent merges the manufacturing of blue, green, and red pixels into a single integrated process using a patterned substrate with mesas of different relaxation rates. All three color pixels are grown simultaneously on the same substrate through selective epitaxy, eliminating the need for separate pick-and-place operations and achieving precise alignment at the micrometer scale.
Solution Approach 2:
The substrate is segmented into mesas with different relaxation rates, where each mesa type (first, second, third) corresponds to a specific color pixel (blue, red, green). This segmentation allows selective epitaxial growth on specific mesa regions, enabling precise spatial control of different color pixels without alignment issues.
2Adaptability or versatility
If quantum dots or nanophosphors are used for color conversion, then color microdisplays can be manufactured, but controlling deposition on small pixels is difficult and resistance to flux is insufficient
Solution Approach 1:
The patent replaces the mechanical deposition process of quantum dots or nanophosphors with a chemical epitaxial growth process. Selective epitaxy allows precise control of material deposition at the atomic level on specific mesa regions, achieving superior deposition control and flux resistance compared to conventional quantum dot approaches.
3Ease of operation
If InGaN material is used to achieve native emission for all RGB pixels, then material consistency is improved, but stress and piezoelectric polarization increase due to high indium concentration requirements
Solution Approach 1:
The patent applies local quality by creating mesas with different relaxation rates in specific locations on the substrate. Each mesa type has tailored stress characteristics that enable high indium concentration InGaN growth for the desired color emission without excessive stress accumulation. The patterned arrangement of different mesa types distributes and manages stress locally across the substrate.
Solution Approach 2:
The patent changes the relaxation rate parameter of the substrate mesas to enable high indium concentration growth. By adjusting the relaxation rate of different mesa types, the patent optimizes the stress state to accommodate the high indium content required for red and green emission while maintaining material quality and reducing piezoelectric polarization effects.
4Illumination intensity
If high indium concentration is used in InGaN quantum wells for red and green emission, then the desired wavelength is achieved, but material quality degrades due to low miscibility of InN in GaN and high compressive stress
Solution Approach 1:
The patent changes the relaxation rate parameter of the substrate mesas to enable high indium concentration growth. By optimizing the relaxation rate, the patent creates a stress environment that accommodates high indium content (35% for red, 25% for green) while maintaining material quality and reducing defects caused by low InN miscibility in GaN.
Solution Approach 2:
Different mesa types are designed with specific relaxation rates optimized for different indium concentrations. mesas for red emission have relaxation rates optimized for 35% In, while mesas for green emission have rates optimized for 25% In, allowing each region to achieve the desired wavelength without material quality degradation.
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 simplifies the manufacturing process, reduces stress and piezoelectric polarization, allows for 'bottom-up' growth of micro-LEDs, and maximizes efficiency by using a single epitaxy step for multiple colors, overcoming alignment issues and enhancing the quality of micro-LEDs.
Implementation Method 1
c) porosifying by electrochemically the doped In(x)GaN layer of the second mesa
Implementation Method 2
InGaN-based blue micro-LEDs already show high luminance... To emit at wavelengths in the green, the quantum wells (QWs) of the LED must contain at least 25% indium and for emission in the red, it is necessary to have at least 35% indium
Implementation Method 3
deposit a first stack on the unintentionally doped In(x)GaN epitaxial recovery layer of the first mesa, whereby a first LED structure is obtained emitting at a first wavelength
Data Source
Figure 1A~1D
Figure 1E~1G
Figure 1H~1J
AI summary
A method for fabricating a native emission matrix comprising the following steps: a) providing a basic structure (10) comprising a substrate (11), a GaN layer (12), a doped ln(x)GaN layer (13) and a nested ln(x)GaN epitaxial recovery layer (14), b) structuring first (S1) and second (S2) mesas in the basic structure (10), the first mesa (S1) comprising a portion of the GaN layer (12), the doped ln(x)GaN layer (13) and the unintentionally doped ln(x)GaN epitaxial recovery layer (14), the second mesa (S2) comprising a portion of the doped ln(x)GaN layer (13) and the unintentionally doped ln(x)GaN epitaxial recovery layer (14), c) porosify the second mesa (S2) by electrochemical means, d) create stacks on the mesas to form LED structures emitting at different wavelengths.