Design optimization of the gallium nitride high electron mobility transistor with graphene and boron nitride heat-spreading elements
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2023-01-01 |
| Journal | Физика и техника полупроводников |
| Authors | V. S. Volcheck, Lovshenko I. Yu., V. R. Stempitsky |
| Institutions | Belarusian State University of Informatics and Radioelectronics |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Advanced Thermal Management for GaN HEMTs
Section titled “Technical Documentation & Analysis: Advanced Thermal Management for GaN HEMTs”This document analyzes the research paper “Design optimization of the gallium nitride high electron mobility transistor with graphene and boron nitride heat-spreading elements” and outlines how 6CCVD’s MPCVD diamond solutions provide superior, scalable alternatives for replicating and advancing this thermal management technology.
Executive Summary
Section titled “Executive Summary”This research demonstrates the critical role of high thermal conductivity materials in mitigating self-heating effects in Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs) through numerical simulation.
- Core Challenge: GaN HEMTs suffer from poor heat dissipation, leading to performance degradation and reliability issues due to localized self-heating.
- Proposed Solution: Integration of high thermal conductivity layers, specifically cubic Boron Nitride ($\beta$-BN) and Graphene, to act as heat-spreading elements.
- Optimization Achievement: A design optimization procedure (Plackett-Burman and full factorial experiments) focusing on geometric parameters (source-gate distance, p-AlGaN thickness, spacer thickness) resulted in an 11.35% increase in output power at 15 V drain-source voltage.
- Thermal Impact: Increasing the $\beta$-BN layer thickness (Y3) from 0.02 µm to 0.18 µm enhanced thermal efficiency by 22.95% and reduced the maximum active area temperature by 28.8 K.
- 6CCVD Value Proposition: While $\beta$-BN and Graphene offer improvements, the literature confirms that MPCVD Diamond offers the highest thermal conductivity, providing the ultimate solution for maximizing power density and reliability in next-generation GaN devices.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the simulation results and material models presented in the paper:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Optimized Output Power (Pout) | 3.63 | W | At VDS = 15 V, VGS = 6 V |
| Output Power Improvement | 11.35 | % | Achieved via geometric optimization |
| Maximum Temperature Reduction | 28.8 | K | Achieved by increasing $\beta$-BN thickness (Y3) |
| $\beta$-BN Thermal Conductivity ($\kappa$) | 8.368 | W/(cm $\cdot$ K) | At 300 K (Table 2) |
| Graphene Thermal Conductivity ($\kappa$) | 20 | W/(cm $\cdot$ K) | Assumed for 10+ atomic layers |
| Sapphire Substrate Thickness | 100 | µm | Default simulation parameter |
| Pyrolytic Graphite Heat Sink Thickness | 20 | µm | Default simulation parameter |
| Optimized Source-Gate Distance (X2) | 1.71 | µm | Critical geometric parameter |
| Optimized p-AlGaN Thickness (Y5) | 0.018 | µm | Critical geometric parameter |
| Optimized Spacer Thickness (Y7) | 0.0022 | µm | Critical geometric parameter |
| Initial Max Temperature (Tmax) | 449.6 | K | Before $\beta$-BN thickness optimization |
| Final Max Temperature (Tmax) | 420.8 | K | After $\beta$-BN thickness optimization |
Key Methodologies
Section titled “Key Methodologies”The research utilized numerical simulation based on coupled Poisson, carrier continuity, and lattice heat flow equations, incorporating temperature-dependent thermal conductivity models.
- Device Structure: A normally-off $\text{AlGaN/AlN/GaN}$ HEMT structure was modeled, featuring a 15 nm $\text{Al}{0.14}\text{Ga}{0.86}\text{N}$ barrier, 2 nm $\text{AlN}$ spacer, 50 nm $\text{GaN}$ channel, and 1.45 µm $\text{GaN}$ buffer layer on a sapphire substrate.
- Heat Spreading Integration: Graphene and cubic Boron Nitride ($\beta$-BN) layers were integrated locally beneath the active area to spread heat toward a pyrolytic graphite heat sink.
- Thermal Modeling: The simulation employed temperature-dependent thermal conductivity models for all materials, including a standard expression $\kappa(T) = \kappa(300\text{K}) (T/300)^{\tau}$.
- Screening Experiment: A Plackett-Burman design was used to screen 18 geometric parameters ($\text{X}1…\text{X}10, \text{Y}1…\text{Y}8$) to identify the three most critical factors influencing output power (X2, Y5, Y7).
- Optimization: A full two-level factorial experiment was performed on the three critical factors to determine the optimal geometric set, resulting in the maximum output power.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”The research confirms that local heat spreading is essential for high-power GaN HEMTs. While $\beta$-BN and Graphene were simulated, MPCVD Diamond is the established industry standard for achieving the highest thermal performance in GaN-on-Diamond architectures. 6CCVD is uniquely positioned to supply the materials necessary to replicate and significantly surpass the thermal performance demonstrated in this study.
Applicable Materials: Diamond for Ultimate Thermal Management
Section titled “Applicable Materials: Diamond for Ultimate Thermal Management”The thermal conductivity of high-quality Single Crystal Diamond (SCD) or Polycrystalline Diamond (PCD) far exceeds the values reported for $\beta$-BN (8.368 W/(cm $\cdot$ K)) and Graphene (20 W/(cm $\cdot$ K)).
| 6CCVD Material Recommendation | Thermal Conductivity ($\kappa$) | Application Context |
|---|---|---|
| Optical Grade SCD | > 20 W/(cm $\cdot$ K) | Ideal for small-area, high-power density devices where maximum thermal extraction is critical. Can be grown as thin films (0.1 µm) for direct integration. |
| High-Quality PCD | 18 - 20 W/(cm $\cdot$ K) | Necessary for scaling up to inch-size wafers (up to 125 mm diameter) for large-scale power electronics manufacturing. Provides excellent lateral heat spreading. |
| BDD (Boron-Doped Diamond) | 10 - 15 W/(cm $\cdot$ K) | If the research were extended to include electrically conductive heat spreaders or electrodes, BDD offers high conductivity with tunable electrical properties. |
Customization Potential for GaN HEMT Integration
Section titled “Customization Potential for GaN HEMT Integration”The paper highlights the need for precise dimensional control and specific material interfaces. 6CCVD provides the necessary engineering services to meet these requirements:
- Custom Dimensions: The simulated device is 1 mm wide. 6CCVD supplies PCD plates up to 125 mm in diameter, enabling the scaling of this optimized HEMT design for commercial production.
- Precise Thickness Control: The study involves thin layers (e.g., 0.002 µm spacer, 0.018 µm p-AlGaN). 6CCVD offers SCD and PCD films from 0.1 µm up to 500 µm thickness, allowing researchers to precisely control the thermal path length (analogous to the optimized Y3 and Y7 parameters).
- Surface Finish: The quality of the diamond/GaN interface is critical for minimizing thermal boundary resistance. 6CCVD guarantees ultra-smooth polishing (Ra < 1 nm for SCD, Ra < 5 nm for inch-size PCD), ensuring optimal thermal contact.
- Custom Metalization: The electrodes in the study were nominally Gold (Au). 6CCVD offers in-house metalization services including Au, Pt, Pd, Ti, W, and Cu deposition, crucial for creating low-resistance ohmic contacts and T-shaped gates directly on the diamond or GaN layers.
Engineering Support
Section titled “Engineering Support”6CCVD’s in-house PhD team specializes in the integration of MPCVD diamond into advanced semiconductor systems. We can assist researchers and engineers in:
- Material Selection: Determining the optimal diamond grade (SCD vs. PCD) and thickness for specific GaN-on-Diamond or GaN-on-SiC projects.
- Thermal Simulation Validation: Providing precise, measured thermal conductivity data for our diamond materials to enhance the accuracy of future numerical simulations, such as those utilizing the temperature-dependent models described in the paper.
- Interface Engineering: Consulting on best practices for minimizing Thermal Boundary Resistance (TBR) between the GaN buffer layer and the diamond heat spreader.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) is standard.
View Original Abstract
The self-heating effect has long been a persistent issue for high electron mobility transistors based on gallium nitride due to their inherently poor heat dissipation capability. Although a wide variety of thermal management solutions has to date been proposed, the problem of the extremely non-uniform heat dissipation at the micrometer scale is still challenging. It has recently been demonstrated, however, that the performance of gallium nitride high electron mobility transistors can be substantially improved by the introduction of various heat-spreading elements based on graphene, boron nitride or diamond. In this paper, using numerical simulation, we carried out a design optimization procedure for a normally-off gallium nitride high electron mobility transistor containing both graphene and cubic boron nitride layers. First, a screening experiment based on a very economical Plackett-Burman design was performed in order to find the most critical geometric parameters that influence the dc characteristics. After that, a full two-level factorial experiment consisting of three factors was implemented and an optimized parameter set was yielded. By applying this set, the output power was increased by 11.35%. The combination of the most significant parameters does not include any factors related to the heat-spreading layers. Keywords: gallium nitride, high electron mobility transistor, optimization, Plackett-Burman design, screening experiment, self-heating.