Glass-Ceramic Substrates for GaN LED Epitaxy
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Solution Overview
Problem
Current LED substrate materials like sapphire and silicon have limited availability and mismatched thermal expansion coefficients with Gallium Nitride (GaN), leading to substrate bow and high crystal defects during GaN growth.
Innovation Solution
Development of glass-ceramic substrates with a coefficient of thermal expansion matching GaN, which are thermally stable up to 1100°C and can be polished to low surface roughness, allowing for scalable GaN thin film growth and epitaxy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sapphire or silicon substrates are used for LED manufacturing, then chemical and thermal durability is achieved, but coefficient of thermal expansion mismatch causes substrate bow and high crystal defects
Solution Approach 1:
The patent changes the thermal expansion parameter by developing glass-ceramic compositions with tailored CTE values (6-14 × 10^-7 /K) that match GaN, while maintaining thermal stability through high processing temperatures (1100-1400°C) and controlled crystallization processes
Solution Approach 2:
The patent uses composite glass-ceramic materials combining crystalline phases (anorthite, cordierite, enstatite, rutile) with residual glassy matrix to achieve both mechanical durability and matched thermal expansion coefficients, eliminating the trade-off between reliability and precision
2Reliability
If sapphire substrates are used, then good chemical and thermal durability is achieved, but availability is limited to sizes smaller than 100 mm diameter
Solution Approach 1:
The patent changes the material composition parameters by formulating glass-ceramics with specific oxide ratios (SiO2: 30-70 wt%, Al2O3: 10-40 wt%, MgO: 5-20 wt%, CaO: 5-15 wt%, TiO2: 1-10 wt%) that enable both durability and scalability to larger substrate sizes
Solution Approach 2:
The patent segments the glass-ceramic into controllable crystalline phases and glassy matrix, allowing independent optimization of each component's properties to achieve both small-grain surface quality and large-substrate manufacturability
3Area of stationary object
If silicon substrates are used, then availability in sizes up to 300 mm diameter is achieved, but coefficient of thermal expansion mismatch causes substrate bow and high crystal defects
Solution Approach 1:
The patent changes the thermal expansion parameter by developing glass-ceramic compositions with tailored CTE values (6-14 × 10^-7 /K) that match GaN, while maintaining thermal stability through high processing temperatures (1100-1400°C) and controlled crystallization processes
Solution Approach 2:
The patent uses composite glass-ceramic materials combining crystalline phases (anorthite, cordierite, enstatite, rutile) with residual glassy matrix to achieve both mechanical durability and matched thermal expansion coefficients, eliminating the trade-off between reliability and precision
4Manufacturing precision
If glass substrates are used to match CTE of GaN, then thermal expansion mismatch is reduced, but thermal stability below 1100°C is insufficient
Solution Approach 1:
The patent utilizes phase transition from glassy to crystalline state through controlled heating (1100-1400°C) and cooling, transforming the material into a thermally stable glass-ceramic that retains CTE matching while gaining high-temperature durability
Solution Approach 2:
The patent changes the material's thermal properties by controlling crystallization temperature and holding time, adjusting the crystalline phase composition to achieve both CTE match and thermal stability simultaneously
5Area of stationary object
If glass-ceramic substrates are prepared in glassy state and cerammed, then scalability to larger wafer sizes is achieved, but additional processing steps are required
Solution Approach 1:
The patent performs preliminary glassy state forming of large substrates before ceramming, allowing easy fabrication of large-area substrates in the flexible glassy state, followed by in-situ crystallization that integrates multiple functions (CTE matching, thermal stability, surface preparation) into a unified process
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 glass-ceramic substrates provide improved thermal stability and reduced defects in GaN crystal quality, enabling larger wafer sizes and volumes with enhanced manufacturing capabilities for LEDs.
Implementation Method 1
The substrate is prepared in the glassy state, formed to the desired shape, and then cerammed to crystallize
Implementation Method 2
After crystallization the substrate is polished to the desired surface roughness
Implementation Method 3
The seed layer provides a template for epitaxial growth of thicker layers at elevated temperatures such as by chemical vapor deposition
Implementation Method 4
both materials differ significantly from GaN in their coefficient of thermal expansion (CTE). This mismatch results in substrate bow during growth
Data Source
AI summary
Embodiments are directed to glass-ceramic substrates with a III-V semiconductor layer, for example, a GaN layer that can be used in LED lighting devices. The glass-ceramics material is in the anorthite-rutile (CaAl2Si2O8+TiO2) family or in the cordierite-enstatite (SiO2—Al2O3—MgO—TiO2) family.