Polycrystalline Ceramic Substrate for CTE-Matched LED Epitaxy
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Solution Overview
Problem
The heteroepitaxial growth of gallium nitride based LED structures on sapphire substrates leads to reduced uniformity and adverse effects on the electronic and optical properties of the epitaxial layers due to mismatched thermal expansion coefficients.
Innovation Solution
A method and system for providing a substrate structure with a coefficient of thermal expansion (CTE) matched to epitaxial layers, involving the fabrication of a ceramic substrate structure with a barrier layer and a bonding layer to facilitate epitaxial growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If heteroepitaxial growth is used to grow gallium nitride LED structures on sapphire substrates, then LED devices can be manufactured, but the mismatched thermal expansion coefficients cause reduced uniformity and adverse effects on electronic and optical properties
Solution Approach 1:
The patent introduces an engineered substrate structure comprising a polycrystalline ceramic core encapsulated in barrier layers and bonding layers that serve as intermediary components between the sapphire substrate and the gallium nitride epitaxial layers. This intermediary structure is designed with a coefficient of thermal expansion substantially matched to the epitaxial layers, thereby reducing thermal mismatch stress and improving uniformity while still enabling LED device manufacturing
Solution Approach 2:
The engineered substrate structure is a composite material system consisting of a polycrystalline ceramic core (such as aluminum nitride or aluminum oxide) encapsulated in multiple layers including barrier layers (e.g., silicon nitride) and bonding layers (e.g., silicon oxide). This composite structure combines materials with different properties to achieve both mechanical integrity and thermal expansion matching, resolving the contradiction between manufacturability and precision
2Productivity
If heteroepitaxial growth is used on sapphire substrates, then LED structures can be produced, but stress increases dislocation density and impairs electrical and optical properties
Solution Approach 1:
The engineered substrate structure acts as a mediator that reduces thermal mismatch stress between the sapphire substrate and the gallium nitride epitaxial layers. By providing a buffer layer with matched thermal expansion properties, the structure prevents stress-induced dislocation formation and maintains high reliability of electrical and optical properties while still enabling efficient LED structure production
Solution Approach 2:
The patent changes the thermal expansion parameter of the substrate system by introducing an engineered substrate with a coefficient of thermal expansion substantially matched to the epitaxial layers. This parameter change reduces thermal stress during temperature cycling, thereby maintaining dislocation density at acceptable levels and preserving electrical and optical properties during manufacturing
3Device complexity
If conventional sapphire substrates are used, then the substrate structure is simple, but thermal expansion mismatch causes stress cracking and device failures
Solution Approach 1:
The patent replaces the simple sapphire substrate with a composite engineered substrate structure consisting of a polycrystalline ceramic core encapsulated in barrier layers and bonding layers. This composite structure provides both mechanical support and thermal expansion matching, preventing stress cracking and improving device lifetime despite the increased structural complexity
Solution Approach 2:
The substrate system is segmented into distinct functional layers: the sapphire substrate, the engineered substrate structure (with ceramic core, barrier layers, and bonding layers), and the epitaxial layers. This segmentation allows each layer to be optimized for its specific function while working together to prevent stress-related failures and improve overall device reliability
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 reduces stress in the epitaxial layers and the substrate, improving the uniformity and performance of the LED structures by matching thermal expansion properties, thereby enhancing electrical and optical properties and reducing defects.
Implementation Method 1
encapsulating the ceramic substrate in a barrier layer
Implementation Method 2
depositing a second bonding layer on the at least a portion of the exposed barrier layer and the fill regions
Implementation Method 3
performing a chemical-mechanical polishing (CMP) process to remove a portion of the bonding layer and to expose at least a portion of the front surface of the ceramic substrate
Data Source
AI summary
An engineered substrate structure includes a ceramic substrate having a front surface characterized by a plurality of peaks. The ceramic substrate includes a polycrystalline material. The engineered substrate structure also includes a planarization layer comprising a planarization layer material and coupled to the front surface of the ceramic substrate. The planarization layer defines fill regions filled with the planarization layer material between adjacent peaks of the plurality of peaks on the front surface of the ceramic substrate. The engineered substrate structure further includes a barrier shell encapsulating the ceramic substrate and the planarization layer, wherein the barrier shell has a front side and a back side, a bonding layer coupled to the front side of the barrier shell, a single crystal layer coupled to the bonding layer, and a conductive layer coupled to the back side of the barrier shell.