GaN Film Structure with Air Cavity for Substrate Deformation
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Solution Overview
Problem
Current methods face challenges in growing high-quality gallium nitride (GaN) crystals on large-area substrates due to differences in lattice constant and thermal expansion coefficients, leading to crystal defects and substrate deformation, especially when using inexpensive glass substrates.
Innovation Solution
A GaN film structure is fabricated using a method that includes a substrate, support members, buffer layers, and an electrode layer, with air cavities formed between the substrate and buffer layers to reduce thermal stress, allowing for the growth of high-quality GaN thin layers on large-area substrates like glass using MOCVD, MBE, or HVPE methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If GaN crystals are grown on large-area substrates, then the production quantity and cost reduction are improved, but substrate deformation occurs due to thermal expansion differences
Solution Approach 1:
The patent divides the continuous buffer layer into multiple discrete support members (pillars) that are distributed across the substrate. This segmentation allows the buffer layer to be supported at multiple points, preventing overall substrate deformation while maintaining structural integrity. The support members are spaced apart to provide localized support without constraining the entire substrate, thus enabling large-area growth without deformation.
Solution Approach 2:
The patent introduces support members as preliminary cushioning structures before GaN crystal growth begins. These support members pre-compensate for the thermal expansion differences that will occur during high-temperature growth, preventing substrate deformation before it happens. The support members absorb and distribute the thermal stress, cushioning the substrate against deformation during the growth process.
2Ease of manufacture
If GaN crystals are grown on glass substrates, then fabrication cost is reduced, but crystal defects increase due to lattice constant differences
Solution Approach 1:
The patent introduces a buffer layer as an intermediary between the glass substrate and the GaN crystals. This buffer layer serves as a transition medium that accommodates the lattice constant mismatch between the glass substrate and GaN. The buffer layer absorbs the lattice mismatch stress, preventing direct transmission of defects to the GaN crystals, thus enabling high-quality crystal growth on inexpensive glass substrates.
Solution Approach 2:
The patent changes the physical and chemical parameters of the interface between substrate and GaN by introducing the buffer layer. The buffer layer has intermediate properties between glass and GaN, creating a gradient transition in lattice constant and thermal expansion coefficient. This parameter transition reduces the abrupt mismatch, thereby reducing crystal defect density while maintaining the use of low-cost glass substrates.
3Ease of manufacture
If GaN crystals are grown on silicon substrates, then substrate cost is reduced, but cracks occur frequently due to thermal expansion coefficient differences
Solution Approach 1:
The patent introduces a buffer layer as an intermediary between the silicon substrate and GaN crystals. This buffer layer mediates the thermal expansion coefficient mismatch between silicon and GaN during high-temperature growth. By absorbing and distributing the thermal stress, the buffer layer prevents crack formation, thereby improving the reliability of GaN crystals grown on cost-effective silicon substrates.
4Manufacturing precision
If sapphire or silicon carbide substrates are used, then crystal quality is improved, but substrate cost increases
Solution Approach 1:
The patent creates a functional copy of the beneficial interface properties found in sapphire or silicon carbide substrates using a buffer layer on inexpensive glass or silicon substrates. The buffer layer replicates the crystallographic and thermal properties needed for high-quality GaN growth, copying the essential characteristics of expensive substrates without requiring the expensive substrate material itself. This allows achievement of similar crystal quality at lower cost.
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 enables the growth of high-quality GaN thin layers on large-area substrates with reduced crystal defects and substrate deformation, facilitating the production of GaN-based semiconductor devices at lower costs.
Implementation Method 1
an electrode layer, which may function as a microheater, are disposed on the first buffer layer
Data Source
AI summary
A method of fabricating a gallium nitride (GaN) thin layer, by which a high-quality GaN layer may be grown on a large-area substrate using an electrode layer suspended above a substrate, a GaN film structure fabricated using the method, and a semiconductor device including the GaN film structure. The method includes forming a sacrificial layer on a substrate, forming a first buffer layer on the sacrificial layer, forming an electrode layer on the first buffer layer, forming a second buffer layer on the electrode layer, partially etching the sacrificial layer to form at least two support members configured to support the first buffer layer and form at least one air cavity between the substrate and the first buffer layer, and forming a GaN thin layer on the second buffer layer.