1. Physical properties of silicon carbide

What is bandgap? The bandgap is expressed as the energy required for an electron in the valence band of an atom to jump (excite) to the conduction band. The band between the valence band and the conduction band is called the forbidden band, and its energy width is called the bandgap. A large bandgap requires more energy for electrical conduction, which leads to less leakage current even at high temperatures when applied to devices.
As a semiconductor material, SiC

・Large bandgap

・Strong bonds between atoms

・High dielectric breakdown electric field

・High saturation drift velocity

・High thermal conductivity

With these characteristics, high-speed and high-voltage power semiconductors have been realized.

 

The bandgap is about 1.12[eV] for silicon (Si) and about 3.26[eV] for silicon carbide (SiC), and the difference between these values means that the bandgap is wide.

2. For power MOSFETs using silicon carbide

The withstand voltage of power devices is determined by the dielectric breakdown electric field and thickness. If the dielectric breakdown electric field is large, it is difficult to break down even in a high electric field, so the thickness of the wafer required to secure the withstand voltage can be reduced. In power MOSFETs, the thinner the wafer, the lower the on-resistance. Applying this feature to power MOSFETs will enable both high breakdown voltage and low on-resistance. The low on-resistance of power MOSFETs is effective in improving conduction losses and suppressing device temperature rises.

In general, the breakdown voltage and on-resistance of power MOSFETs have a contradictory relationship. Saturation drift velocity, which is the velocity of electrons in high electric fields, allows SiC power MOSFETs to switch at high speeds, leading to higher frequencies in application circuits.

As such, SiC power MOSFETs are devices that demonstrate excellent performance in high-voltage, high-power applications.

3. Summary

A comparison with conventional Si products is summarized in the table below.

It is no longer possible to cover everything with conventional power semiconductors alone. We have entered an era where power electronics can tackle social issues such as decarbonization and CO2 reduction with high efficiency. Power semiconductors are diversifying, and SiC power semiconductors, which can achieve low loss, small size, and light weight, are expected to spread to many fields.

Microchip offers a wide range of SiC power device products, including discrete MOSFETs and SBDs, and power modules, with withstand voltages of 700V, 1200V, and 1700V. Especially in power module products, we offer a wide variety of products for each breakdown voltage and topology.

 

The table summarizes the general features assuming high withstand voltage (650V to 1700V). Some Si MOSFETs have low conduction losses in low withstand voltage devices.

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