Large Signal Performance of the Gallium Nitride Heterostructure Field-Effect Transistor With a Graphene Heat-Removal System
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-03-01 |
| Journal | Doklady BGUIR |
| Authors | V. S. Volcheck, V. R. Stempitsky |
| Institutions | Belarusian State University of Informatics and Radioelectronics |
| Citations | 3 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: CVD Diamond for GaN HEMT Thermal Management
Section titled âTechnical Documentation & Analysis: CVD Diamond for GaN HEMT Thermal ManagementâThis document analyzes the research on integrating Chemical Vapor Deposition (CVD) diamond into Gallium Nitride (GaN) Heterostructure Field-Effect Transistors (HEMTs) for enhanced thermal management. The findings directly support the use of 6CCVDâs high-quality Polycrystalline Diamond (PCD) films as critical components in next-generation high-power electronics.
Executive Summary
Section titled âExecutive SummaryâThe research validates the use of high thermal conductivity CVD-diamond integrated into the passivation layer of GaN HEMTs to mitigate self-heating effects and improve large signal performance.
- Core Value Proposition: CVD-diamond, deposited in a trench within the Si3N4 passivation layer, acts as a localized, high-efficiency heat-escape channel directly beneath the hot spot.
- Thermal Performance: The diamond-filled trench system (Variant C) significantly suppresses the self-heating effect, leading to improved device reliability and reduced peak operating temperature.
- Electrical Performance Gains (DC): Integration of the CVD-diamond trench resulted in a 10.4% increase in drain current and a 17.9% improvement in transconductance compared to the baseline HEMT (Variant A).
- RF Performance Gains (2 GHz): Maximum Power-Added Efficiency (PAE) improved from 17.7% (no heat sink) to 18.4% (Variant C), demonstrating superior large signal performance.
- Material Requirement: The success hinges on utilizing high thermal conductivity synthetic diamond (Îș300 = 21.74 W/(cm·K)), a core product line of 6CCVD.
- Methodology: The study utilized rigorous numerical simulation (drift-diffusion theory with lattice heat flow) to accurately model temperature-dependent thermal conductivity (Îș(T)) across all material layers.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the simulation results and material parameters, highlighting the performance impact of the CVD-diamond integration.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| CVD-Diamond Thermal Conductivity (Îș300) | 21.74 | W/(cm·K) | Thermal conductivity at 300 K (Reference [12]). |
| Amorphous Si3N4 Thermal Conductivity | 0.021 | W/(cm·K) | Low conductivity of the passivation layer, necessitating the diamond trench. |
| Maximum Peak Temperature (Variant A) | 340.7 | K | HEMT without heat-removal system (high self-heating). |
| Drain Current Increase (Variant C vs. A) | 10.4 | % | Improvement achieved by adding the diamond trench. |
| Transconductance Improvement (Variant C vs. A) | 17.9 | % | Improvement achieved by adding the diamond trench. |
| Maximum PAE (Variant C) @ 2 GHz | 18.4 | % | Highest Power-Added Efficiency achieved. |
| Maximum PAE (Variant C) @ 4 GHz | 16.5 | % | Highest Power-Added Efficiency achieved. |
| Trench Depth (CVD-Diamond Fill) | 0.19 | ”m | Depth of the trench in the passivation layer. |
| Passivation Layer Thickness (Si3N4) | 0.2 | ”m | Total thickness of the Si3N4 layer. |
| Drain-Source Voltage (VDS) | 15 | V | Operating voltage for large signal simulation. |
Key Methodologies
Section titled âKey MethodologiesâThe experiment modeled a GaN HEMT structure (Variant C) optimized for thermal management. The key steps and material parameters used in the simulation are summarized below:
- Base Structure: GaN HEMT formed on a 50 ”m Sapphire (Al2O3) substrate, featuring a 1.5 ”m GaN buffer layer, 2 nm AlN spacer, and 20 nm Al0.2Ga0.8N barrier layer.
- Passivation: The device was passivated with a 0.2 ”m thick amorphous Silicon Nitride (Si3N4) layer.
- Trench Etching: A 0.19 ”m deep trench was simulated in the Si3N4 passivation layer, located between the gate (0.5 ”m length) and the drain, spanning 4.8 ”m.
- Diamond Deposition: The trench was filled with high thermal conductivity CVD-diamond (synthetic diamond) via simulated Chemical Vapor Deposition (CVD).
- Heat Spreader Integration: A 10 nm Graphene heat-spreading element was placed on the top surface, structurally connected to a heat sink (simulated with Îș = 50 W/(cm·K)).
- Thermal Modeling: Device simulation incorporated the lattice heat flow equation, accounting for temperature-dependent thermal conductivity (Îș(T)) for all materials, including the highly temperature-sensitive CVD-diamond (α = -1.17).
- Simulation Conditions: DC and large signal transient characteristics were calculated at VDS = 15 V and VGS = -2 V, with RF frequencies of 2 GHz and 4 GHz.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the high-performance MPCVD diamond materials required to replicate and advance the thermal management techniques demonstrated in this research. Our capabilities ensure seamless integration into complex GaN HEMT fabrication processes.
Applicable Materials for Thermal Management
Section titled âApplicable Materials for Thermal Managementâ| Application Requirement | 6CCVD Material Recommendation | Technical Rationale |
|---|---|---|
| Trench Filler (0.19 ”m) | Polycrystalline Diamond (PCD) Films | We provide high-quality MPCVD PCD films with thickness control from 0.1 ”m up to 500 ”m, perfectly matching the sub-micron trench depth requirement. Our PCD offers the high thermal conductivity necessary for effective heat extraction. |
| GaN-on-Diamond Substrate | Optical Grade SCD or High-Purity PCD Plates | For maximum thermal performance (Variant C extension), 6CCVD offers diamond substrates up to 125mm diameter, enabling direct GaN growth or wafer bonding for superior heat spreading beneath the entire device structure. |
| High-Purity Heat Spreader | Single Crystal Diamond (SCD) Plates | SCD offers the highest intrinsic thermal conductivity (up to 22 W/(cm·K) at 300 K). We supply SCD plates up to 500 ”m thick for demanding thermal applications requiring maximum heat flux management. |
Customization Potential for HEMT Integration
Section titled âCustomization Potential for HEMT IntegrationâThe successful implementation of this heat-removal system requires precise material engineering and post-processing capabilities, all available in-house at 6CCVD:
- Precision Thickness Control: The research highlights the need for precise deposition thickness (0.19 ”m). 6CCVD guarantees tight tolerance control for both SCD and PCD films, essential for filling trenches or creating thin heat-spreading layers.
- Advanced Polishing: To minimize the critical interfacial thermal resistance (Rth) between the diamond filler/substrate and the GaN layers, 6CCVD offers industry-leading polishing:
- SCD: Surface roughness Ra < 1 nm.
- Inch-size PCD: Surface roughness Ra < 5 nm.
- Custom Metalization Services: The graphene heat-spreading element requires connection to a heat sink. 6CCVD offers internal metalization capabilities, including deposition of standard stacks (Ti/Pt/Au) or custom layers (Au, Pt, Pd, Ti, W, Cu) for ohmic contacts, bonding, or protective layers on the diamond surface.
- Custom Dimensions and Shaping: We provide custom laser cutting and shaping services for diamond plates up to 125mm, ensuring the diamond heat spreader fits specific device geometries and integration requirements.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house team of PhD material scientists specializes in optimizing diamond properties for high-power applications. We offer consultation services to assist engineers and researchers in:
- Selecting the optimal diamond grade (SCD vs. PCD) based on required thermal conductivity and cost constraints.
- Designing integration strategies (e.g., direct CVD growth, wafer bonding, or trench filling) for GaN HEMT thermal management projects.
- Specifying surface preparation and metalization schemes to minimize thermal boundary resistance.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
The self-heating effect exerts a considerable influence on the characteristics of high-power electronic and optoelectronic devices based on gallium nitride. An extremely non-uniform distribution of the dissipated power and a rise in the average temperature in the gallium nitride heterostructure field-effect transistor lead to the formation of a hot spot near the conductive channel and result in the degradation of the drain current, power gain and device reliability. The purpose of this work is to design a gallium nitride heterostructure field-effect transistor with an effective graphene heat-removal system and to study using numerical simulation the thermal phenomena specific to it. The object of the research is the device structure formed on sapphire with a grapheme heat-spreading element placed on its top surface and a trench in the passivation layer filled with diamond grown by chemical vapor deposition. The subject of the research is the large signal performance quantities. The simulation results confirm the effectiveness of the heat-removal system integrated into the heterostructure field-effect transistor and leading to the suppression of the self-heating effect and to the improvement of the device performance. The advantage of our concept is that the heat-spreading element is structurally connected with a heat sink and is designed to remove the heat immediately from the maximum temperature area through the trench in which a high thermal conductivity material is deposited. The results of this work can be used by the electronics industry of the Republic of Belarus for developing the hardware components of gallium nitride power electronics.