Reduction of self-heating effects in GaN HEMT via h-BN passivation and lift-off transfer to diamond substrate - A simulation study
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-01-14 |
| Journal | Materials Science and Engineering B |
| Authors | Fatima Zahrae Tijent, Mustapha Faqir, Paul L. Voss, JeanâPaul Salvestrini, A. Ougazzaden |
| Institutions | International University of Rabat, Georgia Institute of Technology |
| Citations | 7 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis simulation study investigates the use of hexagonal Boron Nitride (h-BN) and diamond substrates to drastically reduce Self-Heating Effects (SHEs) in GaN High Electron Mobility Transistors (HEMTs) for high-power applications.
- Core Value Proposition: The integration of h-BN as a passivation layer and a release layer for transfer onto a high thermal conductivity diamond substrate significantly improves the electrothermal performance of GaN HEMTs.
- Thermal Management Achievement: The maximum lattice temperature (TL,max) was reduced from 507 K (standard SiO2/GaN/sapphire) to 372 K (h-BN/GaN/diamond HEMT).
- Performance Gain: The drain current (IDS) and transconductance (Gm) showed a corresponding 47% improvement due to reduced phonon scattering.
- Thermal Resistance Reduction: The total thermal resistance (Rth) was reduced by a factor of 5, dropping from 27 K.mm/W to 5.5 K.mm/W.
- Reliability Enhancement: The drain current collapse at high bias (VDS = 40 V) was lowered from 46% to 18%.
- Dynamic Response: Transient simulations demonstrated a significantly reduced thermal falling time (790 ns vs. 3.3 ”s), indicating faster thermal recovery and improved reliability for high-frequency switching.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Maximum Lattice Temperature (TL,max) | 507 | K | SiO2/GaN/sapphire HEMT (Device 1) |
| Maximum Lattice Temperature (TL,max) | 372 | K | h-BN/GaN/diamond HEMT (Device 3) |
| Thermal Resistance (Rth) | 27 | K.mm/W | GaN/sapphire HEMT |
| Thermal Resistance (Rth) | 5.5 | K.mm/W | h-BN/GaN/diamond HEMT (5x reduction) |
| DC Performance Improvement | 47 | % | Increase in IDS and Gm after transfer |
| Maximum Drain Current (IDS,max) | 900 | mA/mm | h-BN/GaN/diamond HEMT (VGS = 0 V) |
| Maximum Transconductance (Gm,max) | 250 | mS/mm | h-BN/GaN/diamond HEMT |
| Drain Current Drop (VDS=40 V) | 18 | % | h-BN/GaN/diamond HEMT |
| Transient Falling Time | 790 | ns | h-BN/GaN/diamond HEMT |
| GaN Buffer Layer Thickness | 2 | ”m | Undoped GaN |
| Al0.3Ga0.7N Barrier Thickness | 20 | nm | Active layer |
| AlN Spacer Layer Thickness | 1 | nm | Between GaN and AlGaN |
| Gate Length (LG) | 1.5 | ”m | Device geometry |
| Diamond Thermal Conductivity | ~2000 | W/mK | Ultra-band gap semiconductor |
| TBR (GaN/Diamond Interface) | 10-8 | m2K W-1 | Thermal Boundary Resistance (TBR) used in simulation |
| h-BN In-Plane Thermal Conductivity | 390 - 750 | W/mK | Used for heat spreading layer |
Key Methodologies
Section titled âKey MethodologiesâThe study relied on numerical simulations using Atlas Silvaco TCAD software to model the electrothermal behavior of the GaN HEMT structures.
- Device Structure Definition:
- The simulated structure was GaN/AlN/Al0.3Ga0.7N/GaN.
- Layer thicknesses included a 2 ”m GaN buffer, 1 nm AlN spacer, 20 nm AlGaN barrier, and 2 nm cap layer.
- Gate length was 1.5 ”m, and source-drain spacing was 6 ”m.
- Mobility Modeling: Two low-field mobility models were used: the constant low-field mobility (dependent on TL) and the Farahmand Modified Caughey-Thomas model, fitted to Monte Carlo data. A high-field mobility model was also implemented.
- Thermal Modeling:
- Temperature-dependent thermal conductivity (k(TL)) and heat capacity (C(TL)) models were applied to all materials (GaN, AlN, AlGaN, Sapphire, Diamond, h-BN).
- Thermal Boundary Resistance (TBR) was applied at the substrate interface: 10-7 to 5x10-7 m2K W-1 for sapphire and 10-8 m2K W-1 for diamond.
- h-BN Lift-Off Simulation (Conceptual Transfer):
- Growth: GaN epilayers are conceptually grown on an h-BN/sapphire template.
- Processing: Source, Gate, and Drain electrodes are deposited.
- Release: A water-dissolvable tape is applied, and mechanical force is used to lift the device off the sapphire substrate via the h-BN release layer.
- Bonding: The released GaN HEMT is bonded to the diamond substrate, potentially using a benzo-cyclobutene (BCB) polymer interfacial layer to manage diamond roughness and enhance adhesion.
- Performance Extraction: DC characteristics (IDS, Gm) were extracted at VDS up to 15 V (and 40 V for collapse analysis). Transient simulations were performed by switching VDS from 0 V to 15 V at VGS = 0 V.
Commercial Applications
Section titled âCommercial ApplicationsâThe successful mitigation of SHEs and the resulting performance boost make this h-BN/GaN-on-diamond technology highly relevant for demanding power and RF applications.
- High-Power Switching: Ideal for DC-DC and DC-AC converters, where high efficiency and rapid thermal cycling capability (demonstrated by reduced transient times) are critical.
- RF Power Amplifiers: Enables operation at higher power densities and frequencies (Ka-band and above) by maintaining a low channel temperature, improving output power and reliability.
- Automotive and Electric Vehicle (EV) Systems: GaN HEMTs are crucial for high-efficiency power conversion in EVs; the enhanced thermal stability ensures long device lifetime under harsh operating conditions.
- Aerospace and Defense: Applications requiring robust, high-power-density electronics where weight and volume must be minimized, and thermal stability is paramount.
- 5G/6G Infrastructure: Base station power amplifiers benefit from the improved thermal management, allowing for higher throughput and reduced cooling requirements.
- Advanced Thermal Management: The methodology validates h-BN as an effective top heat spreader, a concept applicable to other semiconductor platforms (SiC, Si) suffering from localized hot spots.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2005 - High-power AlGaN/GaN HEMTs for Ka-band applications [Crossref]
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- 2008 - GaN-based RF power devices and amplifiers [Crossref]
- 2022 - Active thermal management of GaN-on-SiC HEMT with embedded microfluidic cooling [Crossref]
- 2006 - Improved thermal performance of AlGaN/GaN HEMTs by an optimized flip-chip design [Crossref]
- 2003 - Thermal management of AlGaN-GaN HFETs on sapphire using flip-chip bonding with epoxy underfill [Crossref]
- 1987 - The intrinsic thermal conductivity of AIN [Crossref]
- 2010 - AlN passivation over AlGaN/GaN HFETs for surface heat spreading [Crossref]