Patterned Sapphire Substrate Geometry for UV LED Light Extraction
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Solution Overview
Problem
Current patterned sapphire substrates for UV LEDs have design issues due to AlN's small lateral growth rate, leading to thick AlN layers that cause wafer bowing, making mass production difficult, and existing designs lack well-defined principles for light extraction efficiency enhancement.
Innovation Solution
A patterned substrate with nodes and links protruding from a base plane, featuring specific inclination angles and dimensions to enhance light extraction efficiency, allowing for improved epitaxial coalescence and light extraction, with a photolithography mask design that balances filling factor and perimeter ratio for optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If patterned sapphire substrates are used for UV LEDs, then light extraction efficiency is improved, but AlN layer thickness must be increased to achieve smooth epitaxial coalescence, which causes wafer bowing and makes mass production difficult
Solution Approach 1:
The patent changes the geometric parameters of the patterned substrate, specifically optimizing the pitch, depth, and shape of the protrusions and depressions. By adjusting these parameters, the patent achieves smooth AlN epitaxial coalescence at reduced thickness (avoiding the >5-10 μm thickness required by prior art), thereby reducing wafer bowing while maintaining light extraction efficiency improvement
Solution Approach 2:
The patent divides the substrate surface into periodic protrusions and depressions, creating a segmented structure that enhances light extraction through increased scattering. This segmentation also provides more surface area for epitaxial growth, facilitating smoother coalescence at reduced thickness compared to flat substrates
2Stability of the object's composition
If AlN layers are made thick to achieve smooth epitaxial coalescence on patterned substrates, then epitaxial quality is improved, but wafer bowing increases making mass production impossible
Solution Approach 1:
The patent optimizes the geometric parameters of the patterned substrate structure (pitch, depth, shape of protrusions) to achieve the dual benefit of smooth epitaxial coalescence and reduced wafer bowing. The optimized parameters allow AlN layers to coalesce properly at reduced thickness, enabling mass production while maintaining epitaxial quality
3Ease of manufacture
If intuitive design approaches are used for patterned substrates, then implementation is simple, but light extraction efficiency is not optimized for UV LEDs
Solution Approach 1:
The patent establishes specific parameter ranges for the patterned substrate structure (pitch: 2-10 μm, depth: 0.5-5 μm, shape ratios) that are optimized for UV LED light extraction. These quantified parameters replace intuitive designs with science-based optimization, achieving superior light extraction efficiency while maintaining manufacturability through clear design guidelines
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
The substrate design significantly enhances light extraction efficiency for UV LEDs by optimizing the inclination angle of protrusions and balancing the filling factor and perimeter ratio, facilitating smooth epitaxial growth and reducing wafer bowing, thus enabling more efficient mass production.
Implementation Method 1
U.S. Pat. No. 6,091,085 disclosed using surface/interface protrusions and/or depressions to scatter light out of LEDs
Implementation Method 2
AlN is the preferred growth template for UV LEDs in view of the opaqueness of GaN to most of the UV emissions
Data Source
AI summary
A patterned substrate for light emitting diode includes a plurality of nodes and links protruding from a base plane of the substrate and base areas on the substrate, each pair of adjacent nodes is connected by a corresponding link, respectively. The nodes and links also can be concave nodes and concave links cutting into a surface of the substrate, each pair of adjacent concave nodes is connected by a corresponding concave link, respectively.