GaN-on-diamond technology for next-generation power devices
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-03-26 |
| Journal | Moore and More |
| Authors | Kangkai Fan, Jiachang Guo, Zihao Huang, Yu Xu, Zengli Huang |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThe integration of Gallium Nitride (GaN) devices with diamond substrates offers a revolutionary solution to the critical Self-Heating Effect (SHE) that limits high-power density applications.
- Core Problem Mitigation: Conventional substrates (Si, SiC) have low thermal conductivity, leading to localized hot spots and exponential device lifetime reduction (Mean Time To Failure, MTTF).
- Diamond Advantage: Diamond possesses the highest known thermal conductivity (up to 2200 W/mK), enabling rapid heat transfer from the GaN channel to the heat sink, significantly lowering junction temperature.
- Performance Gain: GaN-on-diamond HEMTs have demonstrated output power densities up to 11 W/mm at 10 GHz, and simulations suggest potential for 40 W/mm or greater, far exceeding GaN-on-SiC performance.
- Interfacial Thermal Resistance (TBR): The primary challenge is minimizing TBR at the GaN/Diamond interface, caused by lattice mismatch, defects, and amorphous interlayers. Theoretical minimum TBR is 3 m2K/GW.
- Key Integration Methods: Two main approaches are utilized:
- Bonding: Techniques like Surface Activation Bonding (SAB) achieve low TBR (down to 8.3 m2K/GW) by using ultra-thin dielectric layers (e.g., SiO2) or direct bonding.
- Epitaxial Growth: Chemical Vapor Deposition (CVD) of diamond directly onto the back of the GaN layer, often employing SiNx dielectric layers to protect the GaN and promote diamond nucleation.
- Dielectric Layer Optimization: SiNx is identified as the superior dielectric layer compared to AlN, forming a thin Si-C-N layer that enhances adhesion and lowers TBR (achieved 9.5 m2K/GW).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Thermal Conductivity (K) | 2200 | W/mK | Highest known material K (Table 1) |
| GaN Thermal Conductivity (K) | 230 | W/mK | Conventional substrate comparison (Table 1) |
| SiC Thermal Conductivity (K) | 490 | W/mK | Conventional substrate comparison (Table 1) |
| Diamond Critical Breakdown Field (Ev) | 10,000 | kV/cm | Superior electrical property (Table 1) |
| GaN-on-Diamond TBR (Theoretical Minimum) | 3 | m2K/GW | Diffuse Mismatch Model (DMM) prediction (Table 1, Page 5) |
| GaN-on-Diamond TBR (Achieved, SAB, SiO2) | 8.3 | m2K/GW | Room Temperature SAB with 2.5 nm SiO2 (Table 3) |
| GaN-on-Diamond TBR (Achieved, Epitaxial, AlN) | 9.5 ± 3.8/-1.7 | m2K/GW | MPCVD growth with 5 nm AlN buffer (Table 4) |
| GaN-on-Diamond TBR (Achieved, Epitaxial, SiNx) | 18.2 ± 1.5/-3.6 | m2K/GW | MPCVD growth with 5 nm SiNx buffer (Table 4) |
| GaN HEMT Output Power Density (Achieved) | 11 | W/mm | GaN-on-diamond device at 10 GHz (Page 12) |
| GaN HEMT Output Power Density (Goal) | 40 | W/mm | Target for high-reliability GaN-on-diamond devices (Page 5) |
| GaN HEMT Channel Temperature (Limit) | 200 | °C | Temperature limit at 6 W/mm power density (Page 4) |
| Diamond Debye Characteristic Temperature (Î) | 2220 | K | High vibrational frequency, minimizing phonon scattering (Page 5) |
| Optimal Diamond Substrate Thickness | 100 | ”m | Identified for typical GaN HEMTs (Page 14) |
| CVD Diamond Growth Temperature (High K) | greater than 780 | °C | Required for achieving 900 W/mK thermal conductivity (Page 14) |
Key Methodologies
Section titled âKey MethodologiesâThe integration of GaN and diamond relies on two primary technical approaches, each with specific process parameters and challenges related to minimizing Interfacial Thermal Resistance (TBR).
1. Diamond Bonding Techniques
Section titled â1. Diamond Bonding TechniquesâBonding involves removing the original SiC or Si substrate and directly attaching the GaN epitaxial layer to a pre-prepared diamond substrate.
- Surface Activation Bonding (SAB):
- Process: Surfaces are activated using neutral atom irradiation (e.g., Ar, He, Ne beams) in an ultra-high vacuum (UHV) environment.
- Temperature: Low-temperature (LTB, less than 150 °C) or Room Temperature (RT) bonding is preferred to maintain device quality and minimize thermal stress.
- Interlayers: Dielectric layers (SiNx, AlN, SiO2) are often used to facilitate bonding and control the interface.
- Optimization: Achieving ultra-low TBR (8.3 m2K/GW) requires precise control over the interlayer thickness (e.g., 2.5 nm SiO2) and surface roughness (Root Mean Square, RMS, less than 0.5 nm).
- Van der Waals (VdW) Bonding:
- Process: Transferring AlGaN/GaN RF devices to diamond substrates using VdW forces, followed by thermal annealing to create a robust interface.
- Advantage: Avoids the need for complex dielectric layers, simplifying the process.
2. Epitaxial Growth Techniques (CVD)
Section titled â2. Epitaxial Growth Techniques (CVD)âThis method involves growing diamond directly onto the back of the GaN epitaxial layer, typically using Chemical Vapor Deposition (CVD).
- CVD Methodologies: Hot Filament CVD (HFCVD) or Microwave Plasma CVD (MPCVD) are commonly used.
- Dielectric Layer Function: A dielectric layer is essential for three reasons:
- GaN Protection: Shields the GaN layer from the high-hydrogen plasma environment (95-99% H2 atmosphere) during diamond nucleation, which can otherwise etch the GaN surface.
- Nucleation Aid: Facilitates the nucleation of diamond seed crystals.
- Interface Control: Manages the chemical state and adhesion at the GaN/diamond heterojunction.
- Preferred Dielectric (SiNx): SiNx is preferred over AlN because it forms a thin Si-C-N layer at the interface, which promotes strong chemical bonds with the diamond film, leading to lower TBR.
- Growth Conditions (MPCVD Example):
- Gas Source: CH4 (less than 5%), H2, Ar.
- Temperature: Growth temperatures greater than 780 °C are necessary to achieve high thermal conductivity in the resulting polycrystalline diamond film.
- Alternative Growth: Patterned growth techniques are explored to increase the interface contact area and enhance diamond nucleation density, improving phonon transport efficiency.
Commercial Applications
Section titled âCommercial ApplicationsâGaN-on-diamond technology is positioned to enable next-generation high-performance electronic systems where thermal management is the primary limiting factor.
- High-Power Radio Frequency (RF) Devices:
- Products: High Electron Mobility Transistors (HEMTs) and power amplifiers.
- Context: Used in radar systems and cellular base stations requiring high output power and stable operation under continuous load.
- 5G and Future 6G Communication Networks:
- Products: High-frequency, high-power density components for base stations and network infrastructure.
- Context: Diamond substrates enable the necessary power density and reliability for advanced wireless communication systems (Fig. 12).
- Power Electronics:
- Products: High-voltage, high-temperature power switching devices.
- Context: GaN-on-diamond enhances energy conversion efficiency and extends device lifespan in demanding industrial and automotive applications.
- Microwave Devices and Satellites:
- Products: Components for weather satellites and aerospace applications.
- Context: The mechanical stability and high thermal stability of diamond allow reliable operation under harsh, high-temperature conditions.
- Integrated Circuits (ICs):
- Products: Three-dimensional integrated circuit architectures and miniaturized chips.
- Context: Addresses cooling challenges arising from increased transistor density and miniaturization (Mooreâs Law limits).
View Original Abstract
Abstract Gallium nitride (GaN)-based power devices have attracted significant attention due to their superior performance in high-frequency and high-power applications. However, the high-power density in these devices often induces severe self-heating effects (SHEs), which degrade their performance and reliability. Traditional thermal management solutions have struggled to efficiently dissipate heat, thereby leading to suboptimal real-world performance compared with theoretical predictions. To address this challenge, diamond has emerged as a highly promising substrate material for GaN devices, primarily due to its exceptional thermal conductivity and mechanical stability. GaN-on-diamond technology has a thermal conductivity of 2 200 W/m/K and it significantly enhances heat dissipation at the chip level. In this review, we provide a systematic overview of the two main integration methods for GaN and diamond: bonding and epitaxial growth techniques. Moreover, we elaborate on the impact of thermal boundary resistance (TBR) at the interface. According to the diffuse mismatch model, the TBR of GaN-on-diamond interfaces can be as low as 3 m 2 K/GW, which is markedly superior to silicon carbide substrates. In addition, novel techniques such as patterned growth, nanocrystalline diamond (NCD) capping films, and diamond passivation layers have been explored to further enhance thermal management capabilities. We also consider the roles of intermediate dielectric layers in reducing TBR, promoting diamond nucleation, and protecting the GaN layer. Thus, in this review, we summarize the current state of research into GaN-on-diamond technology, highlighting its revolutionary impact on thermal management for power devices and providing new pathways for the development of high-power GaN devices in the future.