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 |
Executive Summary
Section titled âExecutive SummaryâThis research details the numerical simulation and performance analysis of a Gallium Nitride (GaN) Heterostructure Field-Effect Transistor (HEMT) featuring a novel, enhanced heat-removal system designed to suppress self-heating effects.
- Core Innovation: The proposed device (Variant C) integrates a graphene heat-spreading element on the top surface with a trench in the Si3N4 passivation layer filled with high-thermal-conductivity Chemical Vapor Deposition (CVD) diamond.
- Self-Heating Mitigation: The trench-based system provides a direct heat-escape channel, removing heat immediately from the maximum temperature area (hot spot) near the conductive channel.
- DC Performance Improvement: Variant C demonstrated a 10.4% increase in drain current and a 17.9% improvement in transconductance compared to the standard HEMT without heat removal (Variant A).
- RF Performance Gains (2 GHz): Maximum Power-Added Efficiency (PAE) increased from 17.7% (Variant A) to 18.4% (Variant C). Output power increased by 1.1% and power gain by 2.6% at PIN = 14 dBm.
- RF Performance Gains (4 GHz): Variant C achieved a 5.6% improvement in power gain and a 2.3% increase in output power compared to Variant A, confirming effectiveness at higher frequencies.
- Methodology: The results were obtained via numerical simulation using the classical drift-diffusion model coupled with a lattice heat flow equation that incorporates temperature-dependent thermal conductivity for all material layers.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Substrate Material | Sapphire (Al2O3) | - | Base layer |
| Buffer Layer Material | GaN | - | Thickness: 1.5 ”m |
| Barrier Layer Material | Al0.2Ga0.8N | - | Thickness: 20 nm |
| Passivation Layer Material | Si3N4 | - | Thickness: 0.2 ”m |
| Heat Spreader Material | Graphene | - | Modeled as a conductor |
| Trench Filler Material | CVD-diamond | - | Located between gate and drain |
| Gate Length (LG) | 0.5 | ”m | - |
| Transistor Width | 0.5 | mm | - |
| Drain-Source Voltage (VDS) | 15 | V | Large signal operating point |
| Gate-Source Voltage (VGS) | -2 | V | Large signal operating point |
| Peak Temperature (Variant A) | 340.7 | K | Without heat removal (at VDS = 15 V) |
| CVD-Diamond Thermal Conductivity (K300) | 21.74 | W/(cm·K) | At 300 K |
| Si3N4 Thermal Conductivity | 0.021 | W/(cm·K) | Amorphous layer [13] |
| Max PAE (Variant C, 2 GHz) | 18.4 | % | 0.7% absolute improvement over Variant A |
| Power Gain Improvement (Variant C vs. A, 4 GHz) | 5.6 | % | At PIN = 14 dBm |
Key Methodologies
Section titled âKey MethodologiesâThe device performance was analyzed using numerical simulation based on electro-thermal models:
- Charge Transport Modeling: Simulation was performed using the classical drift-diffusion theory, incorporating doping density and temperature-dependent low- and high-field mobility models.
- Thermal Modeling Integration: A lattice heat flow equation (Equation 1) was added to the semiconductor device equations to accurately model the self-heating effect. Joule heating was considered the dominant heat generation mechanism.
- Temperature-Dependent Thermal Conductivity: The thermal conductivity (Îș) for key materials (AlN, GaN, Al2O3, CVD-diamond) was modeled as a function of temperature (Equation 2), using specific K300 values and temperature dependence coefficients (α).
- AlGaN Modeling: The thermal conductivity of the AlGaN barrier layer was calculated using a composition-dependent formula (Equation 3).
- Graphene Approximation: Since graphene parameters were unavailable in the simulator database, the heat-spreading element was treated as a conductor (part of the drain electrode) with a fixed thermal conductivity of 50 W/(cm·K).
- Boundary Conditions: The temperature at the lower surface of the substrate and the right edge of the heat-spreading element (connected to the heat sink) was rigidly fixed at 300 K.
- Large Signal Analysis: Sinusoidal waveforms (1 V to 4 V amplitude) at 2 GHz and 4 GHz were applied to the gate electrode to calculate output power, power gain, and power-added efficiency (PAE) under heavy distortion conditions.
Commercial Applications
Section titled âCommercial ApplicationsâThe enhanced thermal management provided by the CVD-diamond trench and graphene heat spreader significantly improves the reliability and power density of GaN HEMTs, making them suitable for demanding applications in:
- High-Power RF Electronics: Used in base stations, radar systems, and high-frequency transmitters requiring high power gain and efficiency (e.g., 5G/6G infrastructure).
- Wireless and Satellite Communications: Enabling low-noise operation and high-frequency performance up to the millimeter wave band.
- Power Conversion and Management: Used in high-density power electronics where thermal stability is critical for long-term reliability.
- Defense and Aerospace: Applications requiring robust, high-breakdown voltage transistors capable of operating at high power densities (tens of watts per millimeter).
- High-Speed Networking: Components for Internet and computer networking access systems.
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.