Ceramic Substrate Structure for CTE-Matched Epitaxial Growth
Find Innovative SolutionsGenerate Solutions
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 thermal expansion mismatch.
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 with a barrier layer and a bonding layer to enhance epitaxial growth processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If heteroepitaxial growth is used to grow gallium nitride LED structures on sapphire substrates, then LED devices can be manufactured, but thermal expansion mismatch causes stress that reduces uniformity and degrades electronic and optical properties
Solution Approach 1:
The patent introduces an engineered substrate structure comprising a polycrystalline ceramic core encapsulated in barrier and bonding layers that serves as an intermediary between the sapphire substrate and epitaxial layers. This intermediate structure has a coefficient of thermal expansion substantially matched to the epitaxial layers, reducing thermal mismatch stress while enabling continued manufacturing of LED devices
Solution Approach 2:
The patent employs a composite substrate structure combining polycrystalline ceramic material with encapsulating barrier and bonding layers. This composite construction integrates materials with different properties: the ceramic core provides mechanical support and thermal management, while the encapsulating layers provide stress management and interface compatibility, collectively resolving the thermal expansion mismatch problem
2Productivity
If heteroepitaxial growth process is employed, then LED structures can be produced, but stress increases dislocation density which impairs electrical and optical properties
Solution Approach 1:
The engineered substrate structure acts as a mediator between the growth process and the epitaxial layers. By providing a CTE-matched interface, it reduces stress during epitaxial growth, thereby lowering dislocation density and improving the precision of electrical and optical properties while maintaining production capability
Solution Approach 2:
The patent changes the thermal expansion parameter of the substrate interface by using polycrystalline ceramic material with CTE substantially matched to the epitaxial layers. This parameter change reduces thermal stress during temperature variations in the growth process, leading to lower dislocation density and improved manufacturing precision
3Ease of manufacture
If conventional sapphire substrates are used, then manufacturing is simple, but thermal expansion mismatch causes stress cracking, dislocation glide, and device layer peeling
Solution Approach 1:
The patent creates a composite substrate system that maintains ease of manufacture through established ceramic fabrication processes while adding encapsulating layers that provide stress management. This composite structure prevents stress cracking and delamination by accommodating thermal expansion differences, thereby improving structural integrity without significantly complicating manufacturing
4Productivity
If epitaxial layers are grown on mismatched substrates, then device fabrication can proceed, but thermal stress reduces device performance lifetime
Solution Approach 1:
The CTE-matched engineered substrate serves as a protective intermediary that enables continued device fabrication while reducing thermal stress during operation. This stress reduction prevents stress relaxation, crack propagation, and lattice movement that lead to early failures, thereby extending device performance lifetime
Solution Approach 2:
The patent applies beforehand cushioning by pre-encapsulating the ceramic core in barrier and bonding layers with matched thermal properties before epitaxial growth. This pre-prepared stress-management structure cushions the epitaxial layers against thermal stress during subsequent fabrication and operation, preventing defects and extending device lifetime
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 electrical and optical properties, and extending the device performance lifetime by minimizing defects and thermal mismatch issues.
Implementation Method 1
a coefficient of thermal expansion (CTE) that is substantially matched to epitaxial layers grown thereon
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 voids, and a barrier layer encapsulating the ceramic substrate. The barrier layer defining a plurality of valleys corresponding to the plurality of voids. The engineered substrate structure further includes a first bonding layer comprising a bonding layer material and coupled to the barrier layer on the front surface of the ceramic substrate. The first bonding layer defines a plurality of fill regions filled with the bonding layer material in the plurality of valleys corresponding to the plurality of voids. The engineered substrate structure further includes a second bonding layer coupled to the first bonding layer, and a substantially single crystalline layer joined to the second bonding layer.