Silicon Carbide in Cars, The Wide Bandgap Semiconductor Revolution

Wide bandgap semiconductors , such as silicon carbide (SiC) and gallium nitride (GaN), outperform silicon in terms of efficiency and switching frequency, as well as operating temperature and voltage. EVs and HEVs have multiple power-conversion stages, with cumulative power losses of up to 20% of the initially available power.

WBG Semiconductors significantly improve power conversion stage efficiency, serving as a viable substitute for silicon in the fabrication of voltage converters, power MOSFETs, and high efficiency Schottky diodes. WBG semiconductors offer significant advantages over silicon (Si) and gallium arsenide (GaAs), including higher power efficiency, smaller size, lighter weight, and lower overall cost.

The Advantages of GaN and SiC

Wide bandgap materials have a relatively large energy bandgap, which is the energy gap that exists between the upper limit of the valence band and the lower limit of the conduction band. Electrons can pass through the bandgap and enter the conduction zone via thermal or optical excitation.

Bandgap enables semiconductors to switch between conduction (ON) and interdiction (OFF) states based on electrical parameters that can be controlled from the outside. WBG materials such as silicon carbide and gallium nitride have bandgap values of 3.3 eV and 3.4 eV, respectively, which are significantly higher than those of silicon (1.12 eV) and gallium arsenide (1.4 eV).

A wider bandgap implies a larger electric breakdown field, but it also implies the possibility of operating at higher temperatures, voltages, and frequencies. A large bandgap implies a higher breakdown electric field and, consequently, a higher breakdown voltage.

Overcoming silicon’s theoretical limits, wide bandgap semiconductors such as GaN and SiC provide significant performance improvements and enable efficient and reliable operation even in the harshest conditions. In comparison to silicon, the following are the main advantages of these materials:

  • higher breakdown voltage
  • lower on-resistance
  • operation at higher temperatures
  • excellent high frequency performance
  • higher thermal conductivity
  • near zero reverse recovery time
  • greater reliability

Automotive Applications for Sic 

Figure 1 depicts the main power devices found in any electric or hybrid vehicle: SiC-based devices can effectively replace silicon-based devices in implementing those functionalities. The main inverter is an important part of the vehicle. It is in charge of the electric motor (whether synchronous, asynchronous, or brushless DC) and captures the energy released by regenerative breaking and returns it to the battery.

The DC-DC converter in EVs and HEVs is responsible for supplying the 12V power system bus by converting it from a high-voltage battery. Today, the market offers a variety of high-voltage batteries with varying voltage levels and power classes (typically ranging from 1kW to 5kW).

Other optional components may be required depending on whether the regenerative circuit is intended to support monol or bidirectional energy transfer. Auxiliary inverter/converter provides power from the high-voltage battery to auxiliary systems such as air conditioning, electronic power steering, PTC Heater, oil pumps, and cooling pumps.

During charging and discharging, the battery management system regulates the battery’s state. This operation must be carried out carefully in order to extend the battery’s lifespan. As the age of the battery increases, cell usage must be optimized in order to balance their performance during charging and discharging.

The on-board battery charger is critical because it allows battery charging from a standard power outlet. Because different voltage and current levels must be supported by the same circuit, this is an additional requirement for designers. Future capabilities, such as bi-directional power transfer (where the charger also feeds power from the car to the smart grid), must also be included.

Fig. 1: An HEV/EV is made up of several high-power devices.

Gan Motor Driver

Automotive applications necessitate electric motors that are both smaller and more powerful. Motor driver circuits, which have traditionally relied on MOSFET and IGBT silicon transistors, are finding it increasingly difficult to meet these demands. 

In fact, silicon technology has reached its theoretical limits, with restrictions affecting, among other things, power density, breakdown voltage, and switching frequency, all of which have an impact on power losses.

The main effects of these constraints are primarily manifested in a suboptimal level of efficiency, to which are added potential problems in operation at high temperatures and switching rates. Consider a silicon-based power device with a switching frequency equal to or greater than 40 kHz. Switching losses are greater than conduction losses under these conditions, with cascading effects on overall power losses.

To dissipate the excess heat, a suitable heat sink must be used, a solution that can be disadvantageous due to its large footprint, in addition to levitating costs and device overall weight. High Electron Mobility Transistor (HEMT) devices based on gallium nitride (GaN) exhibit superior electrical properties, making them a viable alternative to MOSFET and IGBT transistors in high voltage and high switching frequency motor control applications.

Figure 2 depicts the overall loss trend for power devices built with silicon and gallium nitride technology. While the conduction losses are constant, the switching losses behave differently in both materials.

The switching losses of a GaN HEMT transistor decrease significantly as the switching frequency increases, and this difference becomes even more pronounced as the switching frequency increases.

Fig. 2: Total device losses for GaN and silicon transistors.

Figure 2 depicts the overall loss trend for power devices built with silicon and gallium nitride technology. While the conduction losses are constant, the switching losses behave differently in both materials.

The switching losses of a GaN HEMT transistor decrease significantly as the switching frequency increases, and this difference becomes even more pronounced as the switching frequency increases.