Recent Progress of Diamond Semiconductor Devices
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-06-04 |
| Journal | Journal of the Japan Society for Precision Engineering |
| Authors | Makoto KASU, Seong-Woo KIM |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research details significant progress in fabricating large-area, high-quality diamond semiconductor wafers and subsequent high-performance power devices, overcoming the size limitations of conventional diamond substrates.
- Wafer Size Achievement: Successfully demonstrated the growth of 2-inch diameter heteroepitaxial diamond wafers, a critical step toward commercial viability, using Microwave Plasma CVD (MPCVD).
- Strain Management: Developed two methods for strain relief: (1) Microneedle-assisted lift-off, enabling self-separation of thick diamond films (500-600 ”m) from the Ir/Sapphire substrate; and (2) Step-Flow Growth on tilted Sapphire substrates.
- Material Quality: Step-Flow Growth on 7° tilted Sapphire yielded the highest quality heteroepitaxial diamond reported globally, achieving a narrow XRC FWHM of 98.35 arcsec (004 reflection).
- Low Dislocation Density: The threading dislocation density was measured at 1.4 x 107 cm-2, confirming the superior crystal quality for heteroepitaxial growth.
- Power Device Performance: Fabricated Diamond Field-Effect Transistors (FETs) utilizing NO2 p-type doping on the (001) layer, achieving a maximum drain current (IDS,max) of 288 mA/mm.
- World-Record Efficiency: The FET demonstrated a world-best Baliga Figure of Merit (BFOM) of 344.7 MW/cm2 and a high breakdown voltage (VBR) up to -2608 V (with passivation).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Band Gap (EG) | 5.47 | eV | Diamond |
| Breakdown Field (EBR) | >10 | MV/cm | Diamond |
| Thermal Conductivity (λ) | 22 | W/cmK | Diamond |
| Electron Mobility (”e) | ~4500 | cm2/Vs | Diamond |
| Hole Mobility (”h) | ~3800 | cm2/Vs | Diamond |
| Wafer Diameter Achieved | 2 | inch | Heteroepitaxial Diamond |
| Substrate Tilt Angle (Optimal) | 7 | ° | Step-Flow Growth |
| Threading Dislocation Density (TDD) | 1.4 x 107 | cm-2 | Heteroepitaxial Diamond (001) |
| XRC FWHM (004 reflection) | 98.35 | arcsec | 7° tilted substrate |
| XRC FWHM (311 reflection) | 175.3 | arcsec | 7° tilted substrate |
| Curvature (Bowing) [1100] direction | 99.64 | cm | 7° tilted self-standing wafer |
| Curvature (Bowing) [0001] direction | 260.21 | cm | 7° tilted self-standing wafer |
| Maximum Drain Current (IDS,max) | 288 | mA/mm | Diamond FET (LG=1.5 ”m) |
| Breakdown Voltage (VBR) | -2608 | V | Diamond FET (with passivation) |
| Baliga Figure of Merit (BFOM) | 344.7 | MW/cm2 | Diamond FET (World-best) |
| High Frequency Power Density (Reported) | 2.1 | W/mm | At 1 GHz |
Key Methodologies
Section titled âKey MethodologiesâThe fabrication process relies on heteroepitaxial growth using Microwave Plasma CVD (MPCVD) on Ir-buffered Sapphire substrates.
- Substrate Selection: Sapphire (a-Al2O3) (1120) orientation was chosen due to its availability in large diameters (up to 8 inches) and its thermal expansion coefficient being closer to diamond than MgO or YSZ, minimizing cracking.
- Buffer Layer Deposition: An Ir buffer layer was deposited onto the Sapphire substrate via sputtering. The epitaxial relationship established is Diamond (001)[110] // Ir (001)[110] // Sapphire (1120)[0001].
- Nucleation: Bias-Enhanced Nucleation (BEN) was performed, where the substrate was negatively biased to accelerate positively ionized methyl (CH3) groups into the Ir surface, promoting diamond nucleation.
- Growth Method 1: Microneedle-Assisted Lift-off (Strain Relief):
- A thin Ni film was deposited and patterned (2 ”m diameter openings, 10 ”m pitch).
- Exposure to H2 gas at ~1000 °C etched the diamond layer beneath the Ni openings, forming 50 ”m tall microneedles.
- A thick diamond layer (800-1000 ”m) was grown over the structure.
- Thermal contraction upon cooling caused the film to fracture at the microneedle layer, enabling self-separation (lift-off) of the 500-600 ”m thick self-standing diamond wafer.
- Growth Method 2: Step-Flow Growth (2-inch Wafer):
- The microneedle process was eliminated.
- Sapphire substrates were intentionally tilted (misoriented) 0° to 7° from the (1120) plane.
- Growth on the 7° tilted substrate maximized crystal quality by allowing residual stress to escape along the tilt direction, enabling crack-free, large-area (2-inch) growth.
- Device Fabrication (FET):
- The (001) heteroepitaxial diamond film was used as the channel layer.
- A p-type hole channel was formed via surface treatment using NO2 doping.
- Source and Drain electrodes were formed using Au/Ni, and the Gate electrode used Al.
- Al2O3 was used as the passivation layer.
Commercial Applications
Section titled âCommercial ApplicationsâThe successful development of large-area, high-quality heteroepitaxial diamond wafers and high-performance FETs targets the next generation of power and high-frequency electronics.
- High-Power Conversion Systems: Diamondâs exceptional thermal conductivity (22 W/cmK) and high breakdown field (>10 MV/cm) make it superior to SiC and GaN for high-voltage, high-current switching applications (e.g., electric vehicles, smart grids, industrial motor drives).
- High-Frequency RF Power Amplifiers: The high carrier mobility and high saturation velocity support applications requiring high power output at high frequencies (e.g., 1 GHz and 120 GHz), such as advanced radar, satellite communications, and 5G/6G mobile base stations.
- Large-Scale Semiconductor Manufacturing: The achievement of 2-inch wafer size using the scalable step-flow growth method is crucial for transitioning diamond devices from laboratory research to industrial mass production.
- Extreme Environment Electronics: The materialâs robustness makes it suitable for electronics requiring operation under high temperatures or harsh radiation environments where silicon-based devices fail.