Introduction

With the rapid development of power electronics, radio frequency (RF) devices, and high-temperature/high-voltage applications, silicon carbide (SiC), a wide-bandgap semiconductor material, has emerged as a critical material in the semiconductor industry. Due to its high breakdown voltage, high thermal conductivity, and excellent high-temperature performance, SiC is increasingly adopted in advanced devices. Among SiC substrates, semi-insulating (SI) SiC substrates are particularly important because they effectively suppress parasitic currents and enhance device performance, especially in RF and microwave applications. Currently, 4-inch SI SiC substrates have become an industrial standard. This article explores their current status, advantages, and future development potential.

1. Technical Background of 4 Inch Semi-Insulating SiC Substrates

1.1 Material Properties of Silicon Carbide

SiC is a wide-bandgap semiconductor (bandgap ~3.26 eV depending on polytype), offering several advantages:

High breakdown voltage: suitable for high-voltage power devices;

High thermal conductivity: facilitates efficient heat dissipation;

High-temperature tolerance: ideal for harsh operating environments.

1.2 Role of Semi-Insulating SiC

SI SiC achieves high resistivity (typically 109∼1012 Ω⋅cm10^9 \sim 10^{12} \ \Omega \cdot cm109∼1012 Ω⋅cm) through controlled doping (commonly with vanadium), which provides:

Suppression of substrate leakage currents;

Improved Q-factor and power efficiency for RF devices;

A stable insulating environment to minimize parasitic effects.

1.3 Maturity of 4-Inch Wafers

A 4-inch wafer (100 mm diameter) offers over twice the area of a 3-inch wafer, enabling more devices per wafer and increasing production efficiency.

The growth technology for 4 inch SI SiC wafers has matured, with controllable defect densities and uniformity suitable for industrial use.

Supporting processes—including polishing, dicing, cleaning, and testing—have achieved mass production capability.

2. Industrial Advantages and Current Applications

2.1 Industrial Adoption

4-inch wafers are widely used in power electronics and RF device manufacturing.

Compared with 6-inch wafers, 4-inch wafers have mature production capacity, moderate cost, and better alignment with current market demand.

2.2 Balance of Cost and Yield

4-inch wafers strike a balance between wafer area, manufacturing cost, and yield.

Larger wafers can increase device count, but excessive size may lead to higher defect rates; 6-inch wafer yield is still improving.

2.3 Major Application Areas

Power devices: MOSFETs, Schottky diodes, for electric vehicles, power modules, and inverters;

RF devices: low-noise amplifiers (LNAs) and power amplifiers (PAs), for 5G communication and radar systems;

High-temperature and high-voltage applications: aerospace, industrial motor control, and other harsh environments.

3. Future Development Potential

3.1 Trend Toward Larger Wafers

As 6-inch SiC wafer technology matures, some power and RF devices may migrate to larger wafers to reduce unit cost.

However, 4-inch wafers will continue to dominate mid- and low-power and RF applications for the foreseeable future.

3.2 Yield Optimization

Defect control in high-quality SI SiC wafers remains critical for cost and device performance.

Technological improvements—including optimized physical vapor transport (PVT) growth, uniform doping, and advanced polishing—can further enhance 4-inch wafer yield.

3.3 Expansion into Emerging Applications

The growing demand from electric vehicles, 5G communications, and renewable energy will continue to drive the need for SI SiC substrates in high-frequency, high-power, and high-temperature applications.

RF microwave devices and monolithic microwave integrated circuits (MMICs) may stimulate further optimization of SI SiC wafers.

4. Conclusion

The 4 inch semi-insulating SiC substrate has become an industrial standard due to:

Technological maturity: stable wafer growth and processing;

Market demand alignment: optimal balance of area and device output;

Industry chain compatibility: well-adapted equipment and processing lines;

Performance-to-cost balance: meets the requirements of power and RF devices.

In the future, as wafer sizes increase and processing techniques improve, 4 inch SI SiC will remain important in mid- and low-power RF applications, while paving the way for wider adoption of 6-inch and larger wafers.