Silicon Carbide Semiconductors in Automotive Drives

Key Takeaways

•  SiC is a compound of silicon and carbide.

• The breakdown field strength of SiC is ten times higher than that of silicon. 

• The bandgap of SiC is three times greater than silicon, which is why SiC devices can operate at higher temperatures.

Earlier this year, I was working on an automotive project to design the inverter for an induction motor drive.  The project had different versions, and the power rating of the motor increased with each. With this increasing power demand, I had to carefully select the inverter switches. I chose silicon carbide (SiC) semiconductor modules over silicon-based discrete devices. SiC semiconductors are next-gen semiconductors that are appealing for high power applications due to their capacity to handle high voltage and high temperatures. Let’s take a closer look at SiC semiconductors and their advantages.

Silicon Carbide Semiconductors

When it comes to semiconductor materials, manufacturers and designers are like-minded; both of them look for a material that can handle high voltage, high current, and high temperature in a small footprint. SiC is a semiconductor material that offers all the properties of silicon along with additional advantages, which is why it is considered a breakthrough development in the semiconductor industry.

SiC is a compound of silicon and carbide (which completely alters the properties of silicon). The limitations of silicon materials in power electronic devices—such as low thermal conductivity, limits in switching frequencies, low bandgap energy, and high device losses—are eliminated with the use of SiC materials. Compared to traditional silicon devices, SiC is the best material for next-generation power electronics. There are several polytypes of SiC available for use in the semiconductor industry, all with different physical properties. 4H-SiC and 6H-SiC are two examples of silicon carbide variants. 

The Advantages of SiC

There are many advantages to silicon carbide semiconductor devices, including:

1. Breakdown field strength: The breakdown field strength of SiC is ten times higher than that of silicon. Comparing a silicon MOSFET with an SiC MOSFET, we can see that the latter offers higher withstanding voltages with lower RDSon resistance, thus reducing conduction losses in the device.  SiC can configure higher voltage power electronic devices due to the presence of a thin drift layer and higher doping levels.  
2. High-speed operation: SiC devices can operate at higher switching frequencies compared to traditional silicon devices. The high-frequency switching in silicon devices results in switching losses and heat generation problems. The intensity of these problems is less in SiC devices due to the improved electrical and thermal conductivity of the material. And, with the incorporation of  SiC high-frequency switching devices, there is a huge reduction in the size of magnetics. 
3. High power efficiency: The power conversion efficiency of SiC power electronics switches is high when compared with silicon-based switches.
4. Wide bandgap and high-temperature operation: The bandgap of SiC is three times greater than silicon; therefore, SiC devices can operate at higher temperatures. The bandgap energy of 2.3 to 3.3 eV makes SiC devices reliable even at temperatures above 200℃. This is an advantage that makes them suitable for use in automotive and spacecraft sectors. And, SiC devices reduce thermal management costs, as they only require basic cooling.
5. Fast reverse recovery characteristics: Similar to silicon-based MOSFETs, SiC MOSFETs also come with an intrinsic body diode. The reverse recovery characteristics of SiC devices are excellent. They offer a short recovery time with negligible recovery current and power loss. 
6. Smaller footprint or die size: SiC carbide switches are most often used in systems handling voltages from 600V. For the given breakdown voltage, the die size of SiC devices is smaller than silicon-based devices. SiC devices and their arrangement in higher power circuits is compact and helps with space-saving. 
7. Long service life: The service lifespan of SiC-based devices is longer than silicon-based devices. 

The aforementioned advantages of SiC semiconductors makes them the best option for high power conversion switching circuits, especially in renewable power generation and battery-powered systems. In the coming years, the demand for silicon carbide semiconductor devices is going to spike as most of the automotive industry shifts to electric vehicle manufacturing.

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