Thermal Modeling of GaN HEMT Devices With Diamond Heat-Spreader
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-01-01 |
| Journal | IEEE Journal of the Electron Devices Society |
| Authors | Marzieh Mahrokh, Hongyu Yu, Yuejin Guo |
| Institutions | Shenzhen Third Peopleâs Hospital, Southern University of Science and Technology |
| Citations | 15 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study uses Finite Volume Method (FVM) thermal analysis (ANSYS Icepak) to model the thermal performance of GaN HEMT devices integrated with single-crystalline CVD-diamond heat spreaders, focusing on the impact of Thermal Boundary Resistance (TBR).
- Core Challenge: Efficient thermal management of high-power density GaN HEMTs is crucial for reliability and performance, requiring integration with ultra-high thermal conductivity materials like CVD-diamond (2000 W/mK).
- Integration Comparison: Two methods were modeled: GaN-on-Diamond (GoD, direct bonding to GaN layer) and GaN/SiC-on-Diamond (GSoD, bonding to the host SiC substrate).
- TBR Sensitivity (GoD vs. GSoD): The GaN-on-Diamond structure exhibits a much higher junction temperature sensitivity to TBR (1.28 °C per unit of TBR) compared to GaN/SiC-on-Diamond (0.43 °C per 10 units of TBR).
- Critical TBR Limit: For the GSoD structure with a 50 ”m SiC layer, the thermal advantage of the immediate proximity of diamond in the GoD structure is lost when the GaN/Diamond TBR exceeds 22 m2K/GW.
- Modeling Accuracy: Using a simplified constant thermal conductivity (K) model significantly overestimates device performance, predicting a junction temperature 17.4 °C lower than the temperature-dependent K model at 10 W/mm areal power density.
- Project Context: This modeling supports an ongoing project focused on in-house growth and bonding of CVD-diamond to GaN PAs for efficient thermal solutions.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Areal Power Density | 10 | W/mm | Standard analysis power dissipation. |
| Hotspot Geometry | 10 x 125 | ”m2 | Modeled GaN HEMT hotspot area. |
| GaN Thickness | 1 | ”m | Active layer thickness. |
| SiC Thickness (GSoD) | 100, 50 | ”m | Intact and thinned substrate versions. |
| CVD-Diamond Thickness | 100 | ”m | Heat-spreader thickness. |
| GaN Thermal Conductivity (300 K) | 125 | W/mK | Room temperature value. |
| SiC Thermal Conductivity (300 K) | 420 | W/mK | Host substrate thermal conductivity. |
| CVD-Diamond Thermal Conductivity (300 K) | 2000 | W/mK | Heat-spreader thermal conductivity. |
| GaN/SiC Interface TBR | 4.4 | m2K/GW | Fixed TBR value used in GSoD model. |
| SiC/Diamond TBR Range | 0 to 75 | m2K/GW | Range investigated for interface bonding quality. |
| GoD TBR Sensitivity | 1.28 | °C per unit of TBR | Junction temperature rise for GaN-on-Diamond (10 W/mm). |
| GSoD TBR Sensitivity | 0.43 | °C per 10 units of TBR | Junction temperature rise for GaN/SiC-on-Diamond (10 W/mm). |
| Critical TBR Limit (GoD vs. GSoD) | ~22 | m2K/GW | TBR threshold where GoD performance drops below GSoD (50 ”m SiC). |
| Modeling Error (Constant K) | 17.4 | °C | Overestimation of performance (lower Tjunction) at 10 W/mm when K(T) is ignored. |
| Base Temperature | 25 | °C | Thermal boundary condition at CuW carrier bottom. |
Key Methodologies
Section titled âKey MethodologiesâThe study utilized the Finite Volume Method (FVM) via ANSYS Icepak to conduct a comparative thermal analysis of two GaN HEMT integration structures:
- Simulation Tool: Finite Volume Method (FVM) implemented in ANSYS Icepak software.
- Device Structures Modeled:
- GaN/SiC-on-Diamond (GSoD): GaN (1 ”m) / SiC (100 ”m or 50 ”m) / AuSn Solder (25 ”m) / CVD-Diamond (100 ”m) / CuW Carrier (1.4 mm).
- GaN-on-Diamond (GoD): GaN (1 ”m) / AuSn Solder (25 ”m) / CVD-Diamond (100 ”m) / CuW Carrier (1.4 mm). (SiC and nucleation layers are etched away).
- Thermal Conductivity Models: Simulations were run using two distinct models to assess accuracy:
- Constant-K Model (using room-temperature K values).
- Temperature-Dependent K Model (K(T)) (using values derived from literature for GaN, SiC, and Diamond).
- Interface Resistance Variation: Thermal Boundary Resistance (TBR) was varied systematically from 0 m2K/GW (ideal) up to 75 m2K/GW at the SiC/Diamond and GaN/Diamond interfaces to simulate varying bonding quality.
- Boundary Conditions: A fixed temperature of 25 °C was applied to the bottom surface of the CuW carrier (base plate).
- Model Validation: Mesh convergence analysis was performed for the FVM model, verifying stability for velocity, continuity, and energy equations.
Commercial Applications
Section titled âCommercial ApplicationsâThe thermal modeling and integration techniques described are critical for advancing high-performance electronic systems where heat dissipation limits power density and reliability.
- 5G Telecommunications: Enabling the high areal power density required for next-generation RF power amplifiers (PAs) and base station infrastructure.
- High Power RF Systems: Essential for military and defense applications, including high-frequency radar, electronic warfare (jammers), and satellite communications.
- Miniaturization of Electronics: Facilitating the reduction in size and weight of GaN devices by allowing higher power dissipation per unit area.
- Reliability Enhancement: Directly improving the operational lifetime and stability of GaN HEMTs by maintaining lower junction temperatures (Tjunction).
- Advanced Packaging: Developing robust wafer bonding methods (Thermo-Compression Bonding, Surface Activated Bonding) for integrating dissimilar materials (GaN/SiC and CVD-Diamond).
View Original Abstract
Harvesting the potential performance of GaN-based devices in terms of the areal power density and reliability, relies on the efficiency of their thermal management. Integration of extremely high thermal conductivity Single-crystalline CVD-diamond serves as an efficient solution to their strict thermal requirements. However, the major challenge lies in the Thermal Boundary Resistance (TBR) at the interface of GaN/Diamond or SiC/Diamond. Junction temperature of the device shows a sensitivity of 1.28°C for every unit of TBR for GaN-on-Diamond compared to 0.43°C for every 10 units of TBR for GaN/SiC-on-Diamond. Finite Volume Thermal Analysis has shown a limit of around 22 m<sup>2</sup>K/GW beyond which the merit of proximity to the heat-source for GaN-on-Diamond can no more outperform GaN/SiC-on-Diamond. Besides, due to the temperature dependency of the thermal conductivity K, an increase in the temperature causes an increase in the thermal resistivity of the device which is more significant in high power operations. Simplified assumption of constant K overestimates the device performance by resulting in 17.4°C lower junction temperature for the areal power density of 10W/mm. Other part of the project regarding the in-house growth of CVD-diamond to be bonded to the GaN device has been simultaneously in progress.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2008 - 55% PAE and high power Ka-band GaN HEMTs with linearized transconductance via n+ GaN source contact ledge [Crossref]