SiC Substrate Wafer Transfer for LED Thermal Management
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Solution Overview
Problem
Conventional semiconductor processing methods for III-nitride electronic devices face challenges such as high substrate costs, thermal management issues, and reduced light extraction efficiency due to the use of non-reusable substrates like sapphire, which lead to current crowding and increased junction temperatures.
Innovation Solution
The use of a SiC substrate with a spreading layer and wafer transfer methods allows for the formation of vertical thin film stacks with thermally conductive SiC contact layers, enabling better current injection and thermal management, and the removal of the substrate for improved light extraction and device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sapphire substrates are used for LED fabrication, then the substrate provides a stable platform for device formation, but the high substrate cost and non-reusability increase device price and waste
Solution Approach 1:
The device structure is segmented into a reusable substrate and a transferable thin film stack. The III-nitride layers are grown as a separate stack on the substrate, then transferred to the final device structure, allowing the substrate to be reused for multiple devices while maintaining stable growth conditions.
Solution Approach 2:
The substrate is discarded after one use and recovered for reuse. By growing the active layers as a transferable stack, the expensive sapphire substrate can be reused multiple times after the thin film stack is transferred to the final device structure, significantly reducing per-device substrate cost.
2Strength
If sapphire substrates are used for LED fabrication, then the substrate provides mechanical support, but the marginal thermal conductivity (42 W/m-k) leads to higher junction temperatures and device degradation
Solution Approach 1:
The thermal management function is extracted from the sapphire substrate by using a separate, highly thermally conductive heat sink structure. The III-nitride active layers are transferred to a structure that incorporates dedicated thermal pathways and heat dissipation mechanisms independent of the substrate material.
Solution Approach 2:
The device structure uses composite materials with superior thermal properties. Instead of relying on sapphire's marginal thermal conductivity, the structure incorporates layers and materials specifically selected for high thermal conductivity to create efficient heat dissipation pathways away from the junction.
3Ease of manufacture
If conventional substrate structures are used with side-to-side contact allocation, then the nonconductive substrate allows contact formation, but current crowding effects occur that degrade carrier injection
Solution Approach 1:
The contact arrangement transitions from a lateral (2D) configuration to a vertical (3D) configuration. By stacking the contacts vertically through the thin film structure rather than placing them side-by-side laterally, current crowding is eliminated and carrier injection is improved while maintaining manufacturing feasibility.
4Use of energy by moving object
If InGaN active layers with high refractive index (nGaN=2.5) are used, then the material provides desired optoelectronic properties, but light extraction efficiency is reduced to only 4% due to total internal reflection
Solution Approach 1:
The planar interfaces are replaced with curved or textured surfaces that reduce total internal reflection. By introducing surface curvature, roughness, or photonic crystal structures, light extraction efficiency is dramatically improved while maintaining the optoelectronic properties of the InGaN active layers.
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 results in enhanced carrier injection, improved light extraction, and reduced junction temperatures, leading to increased device efficiency and longevity, while also allowing for the reuse of substrates and cost reduction.
Implementation Method 1
the spreading layer includes a material having strong bonds in two dimensions and weak bonds in a third dimension
Implementation Method 2
The first contact layer is formed from a thermally conductive crystalline material having a thermal conductivity greater than or equal to that of an active layer material
Implementation Method 3
improved thermal management and produce higher junction temperatures
Data Source
AI summary
A method for wafer transfer includes forming a spreading layer, including graphene, on a single crystalline SiC substrate. A semiconductor layer including one or more layers is formed on and is lattice matched to the crystalline SiC layer. The semiconductor layer is transferred to a handle substrate, and the spreading layer is split to remove the single crystalline SiC substrate.