SiC Devices at a Crossroads: Rapid Advances Amid Ongoing Technical Challenges in Next-Gen Semiconductor Industry

Ⅰ. Silicon Carbide (SiC)

Due to its stable chemical properties, high thermal conductivity, low coefficient of thermal expansion, and excellent wear resistance, silicon carbide (SiC) has applications far beyond its traditional use as an abrasive. For example, SiC powder can be applied to the inner surfaces of turbine impellers or cylinder liners via special processes to enhance wear resistance and extend service life by 1 to 2 times. High-grade refractory materials made from SiC exhibit excellent thermal shock resistance, reduced volume, lighter weight, and high mechanical strength, leading to significant energy-saving benefits.

 

Low-grade silicon carbide (containing approximately 85% SiC) serves as an excellent deoxidizer in steelmaking, accelerating the smelting process, facilitating chemical composition control, and improving overall steel quality. In addition, SiC is widely used in the manufacture of silicon carbide heating elements (SiC rods).

 

Silicon carbide is an extremely hard material, with a Mohs hardness of 9.5—second only to diamond (10). It possesses excellent thermal conductivity and is a semiconductor with outstanding oxidation resistance at elevated temperatures.

 

 

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Ⅱ. Advantages of Silicon Carbide Devices

Silicon carbide (SiC) is currently the most mature wide-bandgap (WBG) semiconductor material under development. Countries around the world place great emphasis on SiC research and have invested substantial resources to promote its advancement.

 

The United States, Europe, Japan, and others have established national-level development strategies for SiC. Major players in the global electronics industry have also invested heavily in the development of SiC semiconductor devices.

 

Compared with conventional silicon-based devices, SiC-based components offer the following advantages:

 

1. High Voltage Capability

Silicon carbide devices withstand voltages up to 10 times greater than equivalent silicon devices. For instance, SiC Schottky diodes can support breakdown voltages of up to 2400 V. SiC-based field-effect transistors (FETs) can operate at tens of kilovolts while maintaining manageable on-state resistance.

 

2. High-Frequency Performance

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3. High-Temperature Operation

With conventional Si devices approaching their theoretical performance limits, SiC power devices are seen as ideal candidates due to their high breakdown voltage, low switching losses, and superior efficiency.

 

However, the widespread adoption of SiC power devices depends on the balance between performance and cost, as well as the ability to meet the high demands of advanced manufacturing processes.

 

 

At present, low-power SiC devices have transitioned from laboratory research to commercial production. However, SiC wafers remain relatively expensive and suffer from a higher defect density compared to traditional semiconductor materials.

 

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Ⅲ. The Most Widely Watched SiC MOS Devices

1. SiC-MOSFET

The SiC-MOSFET (Silicon Carbide Metal-Oxide-Semiconductor Field-Effect Transistor) is currently the most intensively researched power electronic device within the SiC material system. Notable breakthroughs have been made by leading companies such as Cree (USA) and ROHM (Japan).

 

In a typical SiC-MOSFET structure, both the N+ source region and the P-well are formed using ion implantation, followed by annealing at high temperatures (~1700°C) to activate the dopants. One of the critical processes in SiC-MOSFET fabrication is the formation of the gate oxide layer. Given that silicon carbide consists of both Si and C atoms, the growth of gate dielectrics requires specialized oxide growth techniques.

 

Trench Structure vs. Planar Structure

The trench-type SiC-MOSFET architecture maximizes the performance advantages of SiC materials over traditional planar designs. This structure allows for higher current density, lower on-resistance, and better electric field distribution.

 

 

 

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2. Advantages of SiC-MOSFETs

Conventional silicon IGBTs typically operate below 20 kHz. Due to intrinsic material limitations, high-voltage and high-frequency operation is difficult to achieve with silicon-based devices.

 

In contrast, SiC-MOSFETs are well-suited for a wide range of voltage applications—from 600 V to over 10 kV—and exhibit excellent switching characteristics as unipolar devices.

Compared with silicon IGBTs, SiC-MOSFETs offer:

• Zero tail current during switching,
• Lower switching losses,
• Significantly higher operating frequency.

For example, a 20 kHz SiC-MOSFET module can exhibit half the power loss of a 3 kHz silicon IGBT module. A 50 A SiC module can effectively replace a 150 A Si module, highlighting the efficiency and high-frequency performance advantages.

 

Moreover, the body diode in SiC-MOSFETs has ultra-fast reverse recovery characteristics, featuring:

• Extremely short reverse recovery time (trr),
• Very low reverse recovery charge (Qrr).

For instance, at the same rated current and voltage (e.g., 900 V), the Qrr of a SiC-MOSFET’s body diode is only 5% of that of a silicon-based MOSFET. This is particularly beneficial for bridge-type circuits (such as LLC resonant converters operating above resonance), as it:

• Reduces dead-time requirements,
• Minimizes losses and noise from diode recovery,
• Enables higher switching frequencies with improved efficiency.

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3. Applications of SiC-MOSFETs

SiC-MOSFET modules demonstrate substantial advantages in medium- to high-power energy systems, including:

• Photovoltaic (PV) inverters,
• Wind power converters,
• Electric vehicles (EVs),
• Railway traction systems.

Thanks to their high-voltage, high-frequency, and high-efficiency attributes, SiC devices are enabling breakthroughs in EV powertrain design, where traditional silicon devices have reached performance bottlenecks.

 

Prominent examples include:

• DENSO and Toyota, which jointly developed power control units (PCUs) for hybrid electric vehicles (HEVs) and battery electric vehicles (EVs) utilizing SiC-MOSFET modules. These systems achieved a 5x reduction in volume.
• Mitsubishi Electric, which developed a SiC-MOSFET-based EV motor drive system with fully integrated motor and inverter, achieving miniaturization and system integration.

According to projections, SiC-MOSFET modules were expected to see widespread adoption in electric vehicles globally between 2018 and 2020, a trend that continues to grow as technology matures and costs decline.

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Ⅳ. Silicon Carbide Schottky Diodes (SiC SBD)

1. Device Structure

Silicon carbide Schottky diodes adopt a Junction Barrier Schottky (JBS) structure, which effectively reduces reverse leakage current and improves high-voltage blocking capability. This structure combines the advantages of low forward voltage drop and high switching speed.

2. Advantages of SiC Schottky Diodes

As unipolar devices, SiC Schottky diodes offer superior reverse recovery characteristics compared to traditional silicon Fast Recovery Diodes (Si FRDs). When switching from forward conduction to reverse blocking, SiC diodes exhibit:

• Near-zero reverse recovery current: Reverse recovery times are typically less than 20ns; for example, a 600V/10A SiC SBD can achieve under 10ns.
• High switching frequency capability: Enables operation at significantly higher frequencies with improved efficiency.
• Positive temperature coefficient: Resistance increases with temperature, making the devices more suitable for parallel operation and enhancing system safety and reliability.
• Stable switching performance across temperatures: Switching characteristics remain consistent under thermal stress.
• Minimal switching losses: Ideal for high-efficiency applications.

3. Applications

SiC Schottky diodes are widely used in medium- to high-power applications, such as:

• Switching power supplies (SMPS)
• Power factor correction (PFC) circuits
• Uninterruptible power supplies (UPS)
• Photovoltaic inverters and renewable energy systems

Replacing traditional Si FRDs with SiC SBDs in PFC circuits allows operation at frequencies over 300kHz while maintaining efficiency. In contrast, Si FRDs experience a significant efficiency drop beyond 100kHz. Higher frequency operation also reduces the size of passive components like inductors, shrinking overall PCB volume by over 30%.

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Ⅴ. How Is Silicon Carbide (SiC) Regarded?

Silicon carbide is widely recognized as a breakthrough wide bandgap semiconductor material and a leading representative of the third generation of semiconductors. It is praised for its outstanding physical and electrical properties:

1. Material Superiority

• Wide bandgap (3.09 eV): 2.8 times wider than silicon, enabling higher breakdown voltages.
• High breakdown electric field (3.2 MV/cm): 5.3 times higher than silicon, allowing much thinner drift layers.
• High thermal conductivity (4.9 W/cm·K): 3.3 times higher than silicon, facilitating better heat dissipation.
• Strong radiation resistance and high carrier density: Suitable for extreme environments.

2. Electrical Performance

SiC devices offer dramatically improved performance compared to silicon counterparts:

 

• The drift region can be an order of magnitude thinner than that of silicon for the same voltage rating.
• Doping concentrations can be up to two orders of magnitude higher.
• On-resistance per unit area is up to 100 times lower.
• Heat generation is significantly reduced, contributing to lower conduction and switching losses.
• Operating frequencies are typically more than 10 times higher than those of silicon devices.
• SiC devices can function at temperatures up to 400°C and are capable of handling high currents and voltages in compact packages.

 

Recent advancements have made it possible to produce SiC-based IGBTs and other power devices with much lower on-resistance and heat generation. These properties make SiC an ideal material for next-generation power electronics.

 

 

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Ⅵ. Current Development Status of Silicon Carbide (SiC) Devices

1. Technical Parameters

For example, the voltage ratings of Schottky diodes have increased from 250V to over 1000V, while the chip area has decreased. However, the current rating is still only a few tens of amperes. Operating temperatures have improved to 180°C, which is still far from the theoretical maximum of 600°C. The forward voltage drop is also less than ideal—comparable to that of silicon devices—with some SiC diodes exhibiting forward voltage drops as high as 2V.

2. Market Price

SiC devices are approximately 5 to 6 times more expensive than equivalent silicon-based devices.

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Ⅶ. Challenges in the Development of SiC Devices

Based on various reports, the major challenges lie not in device principle or structural design, which can generally be solved, but in the fabrication process. Here are some key issues:

1. Microstructural Defects in SiC Wafers

A major defect is the micropipe, which is visible even to the naked eye. Until these defects are fully eliminated in crystal growth, it's difficult to use SiC for high-power electronic devices. While high-quality wafers have reduced micropipe density to less than 15 cm⁻², industrial applications demand wafers over 100 mm in diameter with micropipe densities below 0.5 cm⁻².

2. Low Efficiency of Epitaxial Growth

SiC homoepitaxy is typically performed via chemical vapor deposition (CVD) at temperatures above 1500°C. Due to sublimation issues, temperatures cannot exceed 1800°C, resulting in low growth rates. While liquid-phase epitaxy allows for lower temperatures and higher growth rates, the yield remains low.

3. Challenges in Doping Processes

Conventional diffusion doping is not suitable for SiC due to its high diffusion temperature, which compromises the masking ability of the SiO₂ layer and the stability of SiC itself. Ion implantation is required, particularly for p-type doping using aluminum.

 

However, aluminum ions cause significant lattice damage and poor activation, requiring implantation at elevated substrate temperatures followed by high-temperature annealing. This can lead to surface decomposition, Si atom sublimation, and other issues. Optimization of dopant selection, annealing temperatures, and process parameters is still ongoing.

4. Difficulty in Forming Ohmic Contacts

Creating ohmic contacts with contact resistivity below 10⁻⁵ Ω·cm² is critical. While Ni and Al are typically used, they suffer from poor thermal stability above 100°C. Composite electrodes such as Al/Ni/W/Au can improve thermal stability up to 600°C for 100 hours, but the contact resistivity remains high (~10⁻³ Ω·cm²), making reliable ohmic contacts difficult to achieve.

5. Heat Resistance of Auxiliary Materials

Although SiC chips can operate at 600°C, supporting materials such as electrodes, solder, packages, and insulation often cannot withstand such high temperatures, limiting the overall system performance.

 

Note: These are just selected examples. Many other fabrication challenges—such as trench etching, edge termination passivation, and the reliability of the gate oxide interface in SiC MOSFETs—still lack ideal solutions. The industry has yet to reach consensus on several of these issues, significantly hindering the rapid development of SiC power devices.

 

 

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Ⅷ. Why SiC Devices Are Not Yet Widely Adopted

The advantages of SiC devices were recognized as early as the 1960s. However, widespread adoption has been delayed due to numerous technical challenges, particularly in manufacturing. Even today, the primary industrial application of SiC remains as an abrasive (carborundum).

 

SiC does not melt under controllable pressure but sublimates at around 2500°C, meaning bulk crystal growth must start from the vapor phase, a much more complex process than silicon growth (Si melts at ~1400°C). One of the biggest obstacles to commercial success is the lack of suitable SiC substrates for power semiconductor devices.

 

For silicon, single-crystal substrates (wafers) are readily available and are the foundation for large-scale production. Although a method for growing large-area SiC substrates (modified Lely method) was developed in the late 1970s, these substrates suffered from micropipe defects.

 

A single micropipe penetrating a high-voltage PN junction can destroy its blocking capability. In the past three years, the micropipe density has dropped from tens of thousands per mm² to tens per mm². As a result, device sizes have been limited to only a few mm², with maximum rated currents of only a few amperes.

 

Further improvements in substrate quality are essential before SiC power devices can become commercially viable.

 

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Ⅸ. Progress in SiC Wafer and Micropipe Density

Recent advancements show that SiC for optoelectronic devices has reached acceptable quality, with production yield and reliability no longer hindered by material defects. For high-frequency unipolar devices such as MOSFETs and Schottky diodes, micropipe density is mostly under control, though it still slightly affects yield.

 

For high-voltage, high-power devices, SiC materials still need another two years of development to further reduce defect density. Despite the current challenges, there is no doubt that SiC is one of the most promising semiconductor materials for the 21st century.

 

 

Ⅹ. Related Products

 

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