High thermal conductivity in wafer-scale cubic silicon carbide crystals
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-11-23 |
| Journal | Nature Communications |
| Authors | Zhe Cheng, Jianbo Liang, Keisuke Kawamura, Hao Zhou, Hidetoshi Asamura |
| Institutions | University of Illinois Urbana-Champaign, Air Water (Japan) |
| Citations | 125 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Thermal Conductivity Breakthrough: Wafer-scale cubic silicon carbide (3C-SiC) crystals achieved an isotropic thermal conductivity (k) exceeding 500 W/mK at room temperature.
- World Ranking: This k value is the second highest among all large crystals (wafer-scale) after single-crystal diamond, and is approximately 50% higher than commercially available 6H-SiC and AlN.
- Puzzle Resolved: The high k confirms theoretical predictions that 3C-SiC, being structurally simpler than 6H-SiC, should have higher k, resolving a long-standing literature puzzle attributed to strong defect-phonon scattering in previous low-quality 3C-SiC samples.
- High Quality & Purity: The observed high k is directly linked to the high crystal quality (XRD FWHM of 158 arcsec) and high purity, with boron (B) impurity concentrations measured below the detection limit (< 3 x 1013 atoms/cm3).
- Thin Film Performance: 3C-SiC thin films demonstrated record-high in-plane and cross-plane k values, surpassing diamond thin films of equivalent thickness.
- Integration Advantage: 3C-SiC can be epitaxially grown on Si, and the resulting 3C-SiC-Si interface exhibits an exceptionally high Thermal Boundary Conductance (TBC) of ~620 MW/m2K.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Bulk Thermal Conductivity (k) | > 500 | W/mK | Isotropic, Room Temperature (RT) |
| Bulk k (Comparison) | ~50% higher | N/A | Compared to c-axis k of 6H-SiC and AlN |
| Wafer Size (Demonstrated) | 2 | inch | Free-standing bulk crystal |
| Wafer Size (Achievable) | Up to 6 | inch | Potential manufacturing scale |
| Crystal Quality (XRD FWHM) | 158 | arcsec | Full Width at Half Maximum of (111) peak |
| Stacking Fault Density | ~1000 | cm-1 | Observed on the growth face |
| Boron (B) Impurity Concentration | < 3 x 1013 | atoms/cm3 | Below SIMS detection limit |
| Nitrogen (N) Impurity Concentration | 5.8 x 1015 | atoms/cm3 | Measured on growth face |
| 3C-SiC-Si TBC | ~620 | MW/m2K | Thermal Boundary Conductance |
| 3C-SiC-Si TBC (Comparison) | ~10 times | N/A | Compared to diamond-Si interfaces |
| Doped 3C-SiC Film k (B-doped) | 324 | W/mK | 1.87 ”m thick film (1-2 x 1019 atoms/cm3 B) |
Key Methodologies
Section titled âKey Methodologiesâ- Crystal Growth: 3C-SiC crystals were grown on (111) Si substrates using Low-Temperature Chemical Vapor Deposition (LT-CVD) in a customized reactor at 1300 K.
- Bulk Sample Preparation: Free-standing bulk 3C-SiC crystals (~100 ”m thick) were obtained by etching away the underlying Si substrate using HNA solution (HF:HNO3:H2O).
- Cross-Plane Thermal Measurement: Thermal conductivity (k) and Thermal Boundary Conductance (TBC) were measured using Time-Domain Thermoreflectance (TDTR) with a 5x objective and 9.3 MHz modulation frequency.
- In-Plane Thermal Measurement: In-plane k of thin films was measured using Beam-Offset Time-Domain Thermoreflectance (BO-TDTR) with a 1.9 MHz modulation frequency.
- Purity Analysis: Secondary Ion Mass Spectrometry (SIMS) was used to profile the atomic densities of key impurities (Boron, Nitrogen, and Oxygen).
- Structural Characterization: Crystal quality was verified using X-ray Diffraction (XRD) rocking curve measurements (FWHM of 158 arcsec) and high-resolution Scanning Transmission Electron Microscopy (HR-STEM) and Selected Area Electron Diffraction (SAED).
- Interface Analysis: Cross-section TEM imaging was used to confirm the sub-nm roughness and quality of the epitaxial 3C-SiC-Si and 3C-SiC-AlN interfaces.
Commercial Applications
Section titled âCommercial ApplicationsâThe combination of high thermal conductivity, high channel mobility (best among SiC polytypes), and compatibility with Si integration positions 3C-SiC as a superior material for next-generation electronics.
- Next-Generation Power Electronics: Use as both active device material (due to high channel mobility) and high-k substrates, offering a significant performance advantage over current 4H-SiC and 6H-SiC.
- High-Power Devices and Modules: The record-high in-plane and cross-plane k in thin films facilitates superior heat spreading and thermal management for localized Joule-heating in high-density electronics.
- Wide-Bandgap Substrates: Serving as high-k substrates for other wide-bandgap materials like GaN, enabling more efficient cooling of GaN-based power amplifiers and RF devices.
- Optoelectronics: Thermal management for high-flux photonic devices where overheating limits performance and reliability.
- Heterogeneous Integration: The high TBC of 3C-SiC-Si interfaces enables efficient thermal integration of 3C-SiC electronics with existing Si electronics.