I. Introduction

Silicon carbide (SiC), as a third-generation wide bandgap semiconductor material, has become a cornerstone for high-frequency, high-power, and extreme-environment electronic devices due to its high thermal conductivity, high breakdown electric field, and excellent radiation resistance. Among them, semi-insulating silicon carbide substrates (SI-SiC), achieved through special doping or compensation processes to obtain high resistivity, are particularly suitable as the base for gallium nitride (GaN) epitaxy. This article focuses on the 3 inch semi-insulating SiC substrate, exploring its current applications, research significance, advantages compared with other sizes, and potential future directions.

II. Applications of 3 Inch Semi-Insulating SiC Substrates

1. RF and Microwave Devices

The 3 inch SI-SiC substrate is currently the mainstream size for GaN-on-SiC epitaxy and is widely used in:

5G base station power amplifiers (PA): meeting high-frequency and high-efficiency requirements;

Radar systems: power amplification modules in X-band, Ku-band, and Ka-band;

Satellite communications (SATCOM): supporting high-power, low-loss signal transmission.

Its high resistivity prevents parasitic current interference, while high thermal conductivity enhances heat dissipation, making it highly effective in high-power, high-frequency applications.

2. Monolithic Microwave Integrated Circuits (MMIC)

The 3-inch SI-SiC substrate provides an ideal low-loss base for MMICs and is widely applied in military electronics, electronic warfare equipment, and high-power microwave devices.

3. High-Reliability Scenarios

Thanks to its stability under high temperature and strong radiation environments, the 3-inch SI-SiC is suitable for aerospace, nuclear systems, and deep space exploration applications.

III. Research Applications and Scientific Value

1. GaN Epitaxy and Defect Studies

The 3-inch substrate is extensively used to investigate defect control, stress management, and step-flow optimization in GaN epitaxial layers, thereby improving epitaxial quality and device reliability.

2. Semi-Insulating Mechanism Research

Through vanadium doping (V-doped) and nitrogen compensation, researchers can use the 3-inch substrate to study deep-level defects, carrier trapping effects, and compensation mechanisms.

3. Novel Device Exploration

Research institutions employ 3-inch SI-SiC for developing optoelectronic devices (UV detectors, radiation detectors) and quantum technologies (quantum bits and quantum sensors based on defect centers), expanding the application scope of SiC.

IV. Advantages Compared with Other Sizes

High technological maturity: Compared to 4-inch and 6-inch larger wafers, the 3-inch substrate features more mature crystal growth techniques and fewer defects.

Balance of cost and performance: The 2-inch substrate is costly with low yield; 4-inch and 6-inch increase throughput but face higher costs and greater growth challenges. The 3-inch substrate provides a balanced option for both research and industrial use.

Broad industrial adoption: Established GaN-on-SiC processes and device designs make the 3-inch substrate the mainstream choice.

Strong equipment compatibility: Most epitaxy tools and production lines are standardized to 3-inch wafers, lowering R&D and manufacturing barriers.

V. Future Research and Application Directions

1. Larger Wafer Sizes and Cost Reduction

Future development will move toward 4-inch, 6-inch, and even 8-inch wafers to meet large-scale industrial demand, while addressing crystal defect density and stress management challenges.

2. High-Frequency and Terahertz Applications

Research on millimeter-wave and terahertz devices based on 3-inch substrates will support 6G communication, satellite internet, and quantum communication.

3. Electronics for Extreme Environments

Studies will focus on the long-term stability of SiC in high-temperature (>600°C) and high-radiation conditions, enabling applications in deep space missions and nuclear energy systems.

4. Emerging Device Directions

Optoelectronics: UV detectors, radiation detectors;

Quantum technologies: quantum bits and quantum sensors based on SiC defect centers.

VI. Conclusion

The 3 inch semi-insulating SiC substrate, with its high thermal conductivity, high resistivity, and technological maturity, plays a critical role in GaN-on-SiC high-frequency, high-power devices, serving as a key material in 5G, radar, and satellite communications. Compared with other sizes, it achieves an effective balance among performance, cost, and maturity. Looking ahead, with the advancement toward larger wafers, terahertz applications, extreme-environment electronics, and novel device exploration, the 3 inch SI-SiC substrate will continue to play an essential role in both research and industry.