Light-Emitting Device Fabrication Using Silicon Substrate and Protective Layer
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Solution Overview
Problem
The high cost of sapphire substrates and the resulting tensile stress due to mismatched coefficients of thermal expansion between sapphire and semiconductor layers in light-emitting devices lead to chipping and cracking issues.
Innovation Solution
A fabrication method involving a growth substrate with a protective layer and a semiconductor layer, where the coefficient of thermal expansion of the substrate is smaller than that of the protective layer and the semiconductor layer, reducing stress and enhancing device stability, using materials like silicon and dielectric materials like SiO2, and forming layers using methods such as MOCVD or MBE.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sapphire substrate is used as growth substrate, then light-emitting device can be fabricated, but cost increases significantly
Solution Approach 1:
The patent replaces expensive sapphire substrates with cheaper silicon substrates that can be discarded after transferring the semiconductor layers. The silicon substrate serves as a temporary growth platform rather than a permanent component, eliminating the need for costly sapphire while maintaining device fabrication capability
Solution Approach 2:
The patent creates a copy of the semiconductor structure on a temporary substrate (silicon), then transfers this copied structure to the final device. The silicon substrate with grown layers becomes a replica that can be separated and used for device assembly, avoiding direct use of expensive sapphire in the final product
2Ease of manufacture
If silicon substrate is used as growth substrate, then manufacturing cost decreases, but tensile stress causes chipping and cracking
Solution Approach 1:
The patent applies preliminary counter-actions by forming protective layers (buffer layer, cladding layer, cap layer) on the silicon substrate before growing semiconductor layers. These protective layers are designed with specific material properties and thicknesses to counteract the tensile stress that would otherwise cause chipping and cracking during device operation
Solution Approach 2:
The patent uses composite material structures consisting of multiple layers (silicon substrate, buffer layer, cladding layer, cap layer, semiconductor layers) with different mechanical and thermal properties. This composite structure balances the thermal expansion coefficients and distributes stress, preventing chipping and cracking while maintaining cost-effectiveness of silicon substrate
3Reliability
If protective layer with higher CTE than substrate is formed, then stress is balanced, but device structure complexity increases
Solution Approach 1:
The patent applies local quality by forming protective layers with specific properties only in certain regions or at specific interfaces where stress concentration occurs. The buffer layer, cladding layer, and cap layer are strategically positioned to provide stress balancing exactly where needed, rather than uniformly throughout the entire device structure
Solution Approach 2:
The patent changes material parameters (thermal expansion coefficient, thickness, composition) of the protective layers to achieve stress balance. By carefully selecting materials with higher CTE than silicon and optimizing their thickness, the patent balances tensile stress without requiring excessive structural complexity
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 method effectively reduces chipping and cracking in light-emitting devices by balancing thermal expansion stresses, improving surface flatness and device reliability.
Implementation Method 1
The coefficient of thermal expansion (CTE) of the silicon substrate 10 is 3.59×10−6 K−1 and the CTE of the semiconductor layer 11 such as gallium nitride (GaN) is 5.59×10−6 K−1. The difference of the coefficient of thermal expansion (CTE) between the silicon substrate 10 and the semiconductor layer 11 is over 50%. The difference of CTE between the semiconductor layer 11 and the silicon substrate 10 provides a tensile stress
Data Source
AI summary
A fabrication method of a light-emitting device comprises providing a growth substrate; forming a protective layer on a first surface of the growth substrate; and forming a first semiconductor layer on a second surface of the growth substrate opposite to the first surface, wherein the coefficient of thermal expansion of the growth substrate is smaller than that of the protective layer and the first semiconductor layer.