GaN-on-diamond technology for next-generation power devices

At a Glance

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

GaN-on-Diamond Technology: Thermal Management Solutions for Next-Generation Power Devices

Executive Summary

This technical review confirms that diamond is the definitive substrate solution for mitigating severe Self-Heating Effects (SHEs) in Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs), driving performance gains necessary for 5G/6G and high-power RF applications.

Superior Thermal Performance: Diamond exhibits exceptional thermal conductivity (K) up to 2200 W/m/K, significantly exceeding SiC (490 W/m/K) and GaN (230 W/m/K), enabling rapid heat transfer from the active channel region.
Low Thermal Boundary Resistance (TBR): The theoretical minimum TBR for the GaN-on-diamond interface is 3 m²K/GW (Diffuse Mismatch Model), markedly superior to conventional substrates.
Integration Methods: Successful integration relies on two primary methods: advanced Surface-Activation Bonding (SAB) and Microwave Plasma Chemical Vapor Deposition (MPCVD) growth of diamond onto the GaN back-side.
Interface Engineering: Minimizing TBR requires precise control of dielectric interlayers (e.g., SiN_x, AlN, SiO₂) and achieving ultra-smooth surface roughness (Ra < 1 nm) for effective phonon coupling.
Achieved Metrics: GaN-on-diamond devices have demonstrated stable operation at high power densities (up to 11 W/mm at 10 GHz) and achieved experimental TBR values as low as 8.3 m²K/GW using optimized bonding techniques.
6CCVD Value Proposition: 6CCVD provides the necessary SCD and PCD substrates, custom dimensions (up to 125mm), and precision polishing required to meet the stringent material specifications for replicating and advancing this critical thermal management technology.

Technical Specifications

Extracted performance metrics and material properties critical for GaN-on-diamond device fabrication and thermal management.

Parameter	Value	Unit	Context
Thermal Conductivity (K)	2200	W/m/K	Single Crystal Diamond (SCD)
Bandgap Energy (E_g)	5.46	eV	Diamond
Critical Breakdown Field (E_v)	10 000	kV/cm	Diamond
Maximum Operating Temperature (T_max)	2100	°C	Diamond
Theoretical Minimum TBR	3	m²K/GW	GaN-on-Diamond (DMM Model)
Lowest Experimental TBR (Bonding)	8.3	m²K/GW	SAB with 2.5 nm SiO₂ interlayer (2024)
Lowest Experimental TBR (CVD)	9.5 ± 3.8/-1.7	m²K/GW	MPCVD with 5 nm AlN interlayer
Optimal Diamond Thickness	100	µm	Simulation for typical GaN HEMTs
Commercial GaN HEMT Power Density	3-8	W/mm	Normal operating conditions (on SiC/Si)
GaN-on-Diamond Power Density	> 40	W/mm	Potential for high-power operation

Key Methodologies

The research paper highlights two primary methods for integrating GaN epitaxial layers with diamond substrates, focusing heavily on minimizing the interfacial thermal boundary resistance (TBR).

Diamond Bonding Techniques:
- Surface-Activation Bonding (SAB): Achieves room-temperature (RT) bonding by activating surfaces using neutral atom irradiation (e.g., Ar ion beam) in a high vacuum, followed by pressure-assisted contact.
- Low-Temperature Bonding (LTB) / High-Temperature Bonding (HTB): Used with intermediate dielectric layers (SiN, AlN, SiO₂) to achieve robust mechanical and thermal junctions.
- Key Requirement: Requires extremely low surface roughness (Ra < 1 nm) on both the GaN and diamond surfaces to ensure close junction and effective phonon transmission.
Epitaxial Growth Techniques (Diamond on GaN Back-Side):
- Microwave Plasma Chemical Vapor Deposition (MPCVD): The preferred CVD method for growing polycrystalline diamond (PCD) films on the back of the GaN epitaxial layer.
- Hot Filament Chemical Vapor Deposition (HFCVD): Also utilized, but MPCVD is often favored for better control over film quality.
- Interlayer Function: A dielectric layer (typically SiN_x or AlN, 5 nm to 40 nm thick) is deposited prior to CVD to protect the GaN layer from the high hydrogen plasma environment and promote diamond nucleation.
- Challenge: CVD-grown diamond starts as nanocrystalline diamond (NCD) near the interface, which has low thermal conductivity, requiring optimization of the nucleation layer thickness and quality.
Thermal Measurement and Characterization:
- Time Domain Thermal Reflectance (TDTR): The standard experimental technique used to accurately measure the TBR at the nanoscale interface.
- Transient Thermal Reflectance (TTR): Used for measuring TBR, particularly in low-temperature bonding studies.
- Raman Thermography: Used to measure the localized junction temperature rise (hot spot) in operating HEMT devices.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials and customization services required to replicate and extend the research presented in this review, accelerating the commercialization of GaN-on-diamond devices.

Applicable Materials

To achieve the highest thermal performance and lowest TBR, researchers require high-quality, high-purity diamond materials.

Material Grade	Description	Application Focus
Optical Grade SCD	Highest purity, lowest defect density SCD.	Ideal for achieving the absolute minimum TBR and maximum thermal conductivity (2200 W/m/K) in critical high-power RF devices.
High-Quality PCD	Polycrystalline diamond wafers up to 125mm in diameter.	Cost-effective solution for large-area GaN-on-diamond integration via MPCVD growth or bonding, suitable for high-volume manufacturing.
BDD (Boron-Doped Diamond)	SCD or PCD doped with Boron.	Available for applications requiring conductive diamond substrates or specialized electrochemical properties (not primary focus of this paper, but available for related research).

Customization Potential

The paper emphasizes the need for precise thickness control (e.g., 100 µm optimal thickness) and interface engineering. 6CCVD’s capabilities directly address these requirements.

Research Requirement	6CCVD Capability	Sales Advantage
Custom Thickness	SCD and PCD wafers available from 0.1µm to 500µm (device layer) and substrates up to 10mm.	We supply the exact 100 µm thickness identified as optimal for GaN HEMT thermal management, ensuring rapid prototyping and optimization.
Ultra-Low Roughness	Precision Polishing achieving Ra < 1nm for SCD and Ra < 5nm for inch-size PCD.	Essential for successful Surface-Activation Bonding (SAB) and minimizing TBR, directly supporting the achievement of sub-10 m²K/GW interfaces.
Interface Metalization	In-house deposition of Au, Pt, Pd, Ti, W, and Cu films.	We provide custom metalization stacks required for electrode contacts, heat spreader layers, or seed layers necessary for subsequent bonding processes (e.g., Ti/Pt/Au stacks).
Large Area Integration	PCD wafers available up to 125mm diameter.	Enables scaling of GaN-on-diamond technology from R&D (3x3 mm chips) to commercial 4-inch and 6-inch wafer fabrication.

Engineering Support

6CCVD’s in-house PhD team specializes in MPCVD diamond growth and material characterization, offering critical support for complex integration challenges.

TBR Optimization: Our experts can assist researchers in selecting the optimal diamond grade (SCD vs. PCD) and surface preparation techniques (polishing grade, orientation) to minimize TBR for specific GaN HEMT designs.
CVD Recipe Consultation: We provide consultation on material specifications necessary for high-quality diamond nucleation layers (NCD) grown via MPCVD, addressing challenges related to hydrogen plasma etching and defect formation.
Application Specific Design: We offer material selection guidance for similar RF, Power Electronics, and Microwave projects requiring advanced thermal management solutions.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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.

Tech Support

Original Source

DOI: https://doi.org/10.1007/s44275-024-00022-z