GaN-on-Diamond Wafer Thermal Management via Composite Substrate
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Solution Overview
Problem
Conventional GaN-based high-electron mobility transistors and similar high-power electronic and optoelectronic devices face thermal performance limitations due to the low thermal conductivity of their substrates, which restricts their efficiency and reliability, especially in high-power applications.
Innovation Solution
The integration of GaN with highly thermally conductive synthetic diamond substrates through methods like chemical vapor deposition, where a diamond layer is grown on a dielectric layer disposed on top of wide-gap compound-semiconductor layers, forming GaN-on-diamond engineered wafers to enhance thermal management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional substrates (silicon, GaAs, InP, sapphire) are used for GaN device growth, then device manufacturing is feasible with standard processes, but thermal resistance is high which limits power handling and reliability
Solution Approach 1:
The patent employs a composite substrate structure consisting of a diamond layer grown on a GaN buffer layer, which itself is grown on a conventional substrate (silicon, sapphire, or SiC). This composite structure combines the manufacturing advantages of conventional substrates with the superior thermal conductivity of diamond, achieving low thermal resistance while maintaining device manufacturability. The diamond layer thickness is optimized at 1-100 micrometers to balance thermal performance with mechanical stability and manufacturing feasibility.
2Temperature
If diamond substrates are used directly for GaN growth, then thermal conductivity is maximized, but lattice mismatch causes high dislocation density and poor crystal quality
Solution Approach 1:
The patent segments the substrate structure into multiple functional layers: a conventional substrate providing mechanical support and ease of manufacturing, a GaN buffer layer that serves as an intermediate transition layer, and a diamond layer providing thermal management. This segmentation allows each layer to fulfill its specific function optimally - the buffer layer accommodates lattice mismatch through controlled dislocation filtering, while the diamond layer provides thermal conductivity without directly contacting the GaN active layers.
Solution Approach 2:
The GaN buffer layer acts as an intermediary between the conventional substrate and the diamond layer. It provides a lattice-matched foundation for growing high-quality GaN active layers while allowing the diamond layer to be grown on top for thermal management. The buffer layer thickness is optimized at 1-10 micrometers to filter dislocations while maintaining structural integrity, effectively mediating between the thermal requirements and crystal quality requirements.
3Temperature
If thin diamond layers are used to reduce thermal resistance, then thermal performance improves, but mechanical strength and structural stability decrease
Solution Approach 1:
The patent optimizes the diamond layer thickness parameter within the range of 1-100 micrometers to achieve the desired balance between thermal performance and mechanical strength. This parameter optimization allows sufficient diamond thickness to provide effective thermal management while maintaining adequate mechanical strength for device fabrication and operation. The exact thickness is selected based on the specific application requirements for power handling versus mechanical robustness.
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 significantly reduces thermal resistance, thereby improving the performance and reliability of GaN-based devices by leveraging diamond's high thermal conductivity, enabling better heat dissipation and maintaining device performance over temperature.
Implementation Method 1
Diamond wafers are manufactured by chemical vapor deposition (CVD) by one of three methods: plasma enhanced diamond CVD where the energy to dissociate the reactants comes from a microwave source, hot-filament enhanced diamond CVD where the energy for dissociating gases comes from a hot tungsten filament, and high voltage torch where ions are accelerated using a high DC voltage
Implementation Method 2
plasma enhanced diamond CVD where the energy to dissociate the reactants comes from a microwave source
Data Source
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AI summary
A method for integrating wide-gap semiconductors, and specifically, gallium nitride epilayers, with synthetic diamond substrates is disclosed. Diamond substrates are created by depositing synthetic diamond onto a nucleating layer deposited or formed on a layered structure that comprises at least one layer of gallium nitride. Methods for manufacturing GaN-on-diamond wafers with low bow and high crystalline quality are disclosed along with preferred choices for manufacturing GaN-on-diamond wafers and chips tailored to specific applications.