Thick GaN LED Stacks for Thermal and Mechanical Integrity
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Solution Overview
Problem
Conventional solid-state light sources face issues with the fragility and cost of GaN-based LEDs due to their thin semiconductor layers, inefficient wavelength conversion using phosphor powders, and the need for substrates that hinder thermal conductivity and light extraction.
Innovation Solution
Development of a solid-state light source comprising a stack of substrate-free inorganic LED chips and wavelength conversion chips, where the LED chips have thick epitaxial layers for structural support and the wavelength conversion chips include electrical interconnections, allowing for improved thermal conductivity and light extraction without the need for growth or transfer substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional thin GaN-based LED layers are used, then manufacturing cost is reduced and fabrication is simpler, but the LED chips become fragile and break easily
Solution Approach 1:
The patent applies preliminary action by growing thick semiconductor layers (10-50 micrometers) directly on the sapphire substrate during the epitaxial growth process itself, rather than attempting to transfer thin layers later. This preliminary thick-layer growth ensures structural integrity is established before any potential handling or processing steps, resolving the fragility issue while maintaining manufacturing simplicity.
Solution Approach 2:
The patent changes the critical parameter of layer thickness from the conventional 3 micrometers to 10-50 micrometers. This parameter change fundamentally alters the mechanical properties of the LED structure, providing sufficient thickness to prevent breakage during handling and processing while still maintaining the electrical and optical functionality of the device.
2Manufacturing precision
If sapphire substrates are used for GaN-based LEDs, then crystallographic matching is improved, but thermal conductivity deteriorates
Solution Approach 1:
The patent applies segmentation by dividing the LED structure into distinct functional layers grown on the sapphire substrate. The thick active semiconductor layers (10-50 micrometers) are grown directly on the substrate, creating a segmented structure where the substrate provides crystallographic support while the thick semiconductor layers provide the light-emitting function and improved thermal pathways.
Solution Approach 2:
The patent changes the thickness parameter of the semiconductor layers to 10-50 micrometers, which is sufficiently thick to provide alternative thermal conduction pathways through the semiconductor material itself, partially compensating for the poor thermal conductivity of the sapphire substrate while maintaining the crystallographic benefits of the substrate.
3Ease of manufacture
If wafer bonding techniques are used to attach LED layers to transfer substrates, then substrate removal is enabled, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies the taking out principle by completely eliminating the substrate removal step and the transfer substrate concept. Instead of growing thin layers on a substrate and then removing the substrate, the patent grows thick layers directly on the final sapphire substrate, which is retained as part of the final device structure. This extracts the unnecessary complexity of wafer bonding and substrate removal from the manufacturing process.
Solution Approach 2:
The patent applies preliminary action by establishing the thick-layer structure directly on the sapphire substrate during the initial epitaxial growth process, before any device fabrication steps. This preliminary structuring eliminates the need for subsequent substrate manipulation, bonding, or removal operations, simplifying the overall manufacturing process.
4Illumination intensity
If conventional packaged LEDs with phosphor particles in polymer are used, then wavelength conversion is achieved, but the package becomes bulky and light extraction efficiency is reduced
Solution Approach 1:
The patent applies composite materials by integrating the phosphor wavelength conversion layer directly with the LED chip structure in a monolithic configuration. The phosphor particles are embedded in a transparent matrix that is deposited directly on the LED chip, creating a composite structure that eliminates the need for separate polymer encapsulation and reduces overall package volume while maintaining wavelength conversion functionality.
Solution Approach 2:
The patent merges the wavelength conversion function with the LED chip structure itself by depositing the phosphor layer directly on the chip surface. This merging eliminates the separate packaging step and reduces the distance light must travel through packaging materials, thereby reducing package size and improving light extraction efficiency while maintaining the wavelength conversion capability.
5Illumination intensity
If standard LED/phosphor packages are used, then complete light conversion is achieved, but production cost increases
Solution Approach 1:
The patent merges the LED chip fabrication and phosphor deposition into a single integrated manufacturing process. The phosphor layer is deposited directly on the LED chip in the same fabrication environment, eliminating separate packaging operations and reducing production costs while achieving complete wavelength conversion in a single integrated structure.
Solution Approach 2:
The patent uses composite materials by integrating the phosphor wavelength conversion layer directly with the LED chip structure. This composite approach allows both components to be manufactured together in a single process flow, reducing the number of manufacturing steps and associated costs while achieving complete light conversion functionality.
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 solution enhances the thermal conductivity and light extraction efficiency of the LED chips, reducing production costs and improving the durability and performance of the light source, enabling the creation of distributed light sources that meet safety standards and operate efficiently at lower current densities.
Implementation Method 1
The inorganic LED chip emits internally generated light of a first wavelength range
Implementation Method 2
The wavelength conversion chip converts at least a portion of the light of a first wavelength range into light of a second wavelength range
Data Source
AI summary
A solid-state light source includes at least one stack of light emitting elements. The elements are an inorganic light emitting diode chip and at least one wavelength conversion chip or the elements are a plurality of light emitting diode chips and one or more optional wavelength conversion chips. The wavelength conversion chip may include an electrical interconnection means. The light emitting diode chip may include at least one GaN-based semiconductor layer that is at least ten microns thick and that is fabricated by hydride vapor phase epitaxy. A method is described for fabricating the solid-state light source.