GaN HEMT Backside Electrode Layout for Heat and Inductance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional GaN HEMTs face challenges with high production costs, limited breakdown voltage, overheating due to low thermal conductivity of sapphire substrates, and parasitic inductance issues, making them unsuitable for commercial applications in power sources and RF devices.
Innovation Solution
A GaN HEMT design incorporating a heat dissipation structure with a molybdenum substrate and conductive channels to dissipate heat efficiently, while guiding electrodes to the backside for traditional packaging, reducing parasitic inductance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a single-crystal sapphire substrate is used for GaN HEMT, then the breakdown voltage can reach close to 650 V with thin epitaxial layer (2.5 μm), but the thermal conductivity is too low (0.47 W/cmK) causing overheating
Solution Approach 1:
The patent uses a composite substrate structure combining sapphire and silicon carbide (SiC) layers. The sapphire layer provides high breakdown voltage performance, while the SiC layer provides high thermal conductivity for effective heat dissipation. This composite structure resolves the contradiction between achieving high breakdown voltage and maintaining effective heat dissipation.
2Temperature
If a single-crystal SiC substrate is used for GaN HEMT, then the thermal conductivity is high (4.5 W/cmK) for good heat dissipation, but the cost is too high limiting commercial application
Solution Approach 1:
The patent creates a cost-effective composite substrate using cheaper sapphire as the base material with a thinner SiC layer (0.5-2.0 μm) only where needed for heat dissipation. This reduces the overall SiC material cost compared to using full-thickness SiC substrates, while still achieving adequate thermal management performance.
Solution Approach 2:
The SiC layer is applied locally rather than uniformly throughout the entire substrate structure. The SiC is concentrated in regions where heat dissipation is most critical, while other areas use the cheaper sapphire material, optimizing the cost-performance balance.
3Ease of manufacture
If a single-crystal Si substrate is used for GaN HEMT, then the cost is lower than SiC substrate, but the epitaxial thickness must be at least 5.0 μm to achieve breakdown voltage close to 650 V, and thermal expansion coefficient difference is 50% requiring superlattice structure
Solution Approach 1:
The sapphire-SiC composite substrate provides a better lattice match for GaN epitaxy compared to Si substrates, reducing the need for thick epitaxial layers and complex superlattice structures. This achieves high breakdown voltage with thinner, more cost-effective GaN layers.
Solution Approach 2:
The patent changes the substrate material parameters (thermal conductivity, thermal expansion coefficient, lattice constant) by using sapphire-SiC composite instead of pure Si, which improves both the breakdown voltage performance and reduces the complexity of the epitaxial growth process.
4Device complexity
If electrode structures are formed on front side only, then the device structure is simple, but parasitic inductance is high affecting RF performance
Solution Approach 1:
The patent extends the electrode structures into the vertical dimension by creating conductive channels that penetrate through the substrate thickness. This allows electrodes to be positioned on both front and back sides of the device, forming three-dimensional current paths that reduce parasitic inductance while maintaining manageable 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
Enhances breakdown voltage, improves heat dissipation, and reduces parasitic inductance, enabling cost-effective commercial application in power sources and RF devices.
Implementation Method 1
a heat dissipation structure for dissipating heat generated by the transistor structure
Implementation Method 2
The at least one conductive structure is disposed in the at least one channel, and has two opposite ends respectively electrically connected to the heat dissipation metal unit and the electrode unit
Implementation Method 3
the single-crystal GaN is usually crystallized on a single-crystal silicon carbide (SiC) substrate, a single-crystal Si substrate, or a single-crystal sapphire substrate in the heteroepitaxial manner
Data Source
AI summary
A gallium nitride high electron mobility transistor includes a transistor structure, a heat dissipation structure for dissipating heat generated by the transistor structure, and at least one conductive structure. The transistor structure includes a composite semiconductor unit and an electrode unit. The composite semiconductor unit includes a gallium nitride layer. The heat dissipation structure includes a heat dissipation insulating layer and a heat dissipation metal unit. The heat dissipation metal unit includes a molybdenum substrate. The heat dissipation structure and the transistor structure cooperatively define at least one channel penetrating from a side of the heat dissipation insulating layer to the electrode unit. The conductive structure is disposed in the channel, and has two opposite ends respectively electrically connected to the heat dissipation metal unit and the electrode unit. A method for manufacturing a gallium nitride high electron mobility transistor is also provided.