FAQs about SiC Semiconductor
FAQs about SiC Silicon Carbide Semiconductor
What is SiC?
SiC (silicon carbide) is a compound semiconductor composed of silicon and carbide. Combining silicon and carbon results in superior mechanical, chemical, and thermal properties. A variety of polytypes (polymorphs) of SiC exists, each with different physical properties.
Here listed some key properties it has:
- High strength
- High melting point
- Low thermal expansion
- Excellent thermal shock resistance
- Superior chemical inertness
- High hardness
- Resistance to corrosion
- High thermal conductivity
- High elastic modulus
- Functions as a semiconductor
- Robust crystal structure
What is the advantage of SiC semiconductor?
In terms of materials, the main advantages of SiC over silicon materials are:
- high voltage resistance, breakdown field strength is 10 times of Si, the same voltage level of SiC MOS wafer epitaxial layer thickness only needs one tenth of Si, band gap width is 3 times of Si, stronger conductivity;
- high temperature resistance, thermal conductivity and melting point is very high, is 2-3 times of Si;
- high frequency, electron saturation speed is 2-3 times that of Si, can achieve 10 times of working frequency.
In terms of device, the main advantages of SiC devices over Si devices come from three aspects:
- the small on-state resistance, and then reduce the area of the chip, SiC power module size can reach about 1/10 Si.
- the higher working frequency can achieve high-speed switching, thus effectively reducing the size of passive components such as inductance and capacitance, and the size of peripheral components is more miniaturized.
- more high temperature resistance, SiC band gap width is higher, the corresponding intrinsic temperature can be up to 800 degrees, in addition, SiC material thermal conductivity is higher, the design of the heat dissipation system is simpler, or directly use natural cooling.
In addition, a greater significance of SiC in practical application lies in the fact that SiC MOSFET devices can be prepared and applied to high voltage fields to achieve lower loss.
IGBT widely used in the field of high voltage and high power is bipolar device, which has a trailing current during shutdown, resulting in relatively large shutdown loss. While MOSFET is a monopole device, there is no trailing current, when using SiC material to prepare MOSFET, the on-resistance and switching loss of the device is greatly reduced.
Here is a brief comparison between MOSFET and IGBT:
- MOSFET has shorter switching time and faster response speed, and has more advantages than IGBT in the field of higher frequency requirements, but Si based MOSFET is not suitable for high-power devices.
- IGBT can support high voltage, very suitable for inverter such high voltage, high current, high power applications, but in high frequency scenarios, the disadvantage is obvious, and the switching loss is significantly greater than MOSFET.
Where is SiC used?
Silicon carbide is one of the third generation of semiconductor materials and have high power, low loss, high reliability, low heat dissipation, etc, can be applied to more than 1200 volts high-pressure, harsh environment, can be widely used in wind power, railway, transport, and solar inverters, uninterruptible power system, intelligent power grid, power supply, high power applications.
What is the specific application of silicon carbide SiC semiconductor in electric vehicles?
In electric vehicles, SiC devices mainly have three application scenarios: vehicle-mounted OBC (vehicle-mounted charger), DC/DC (DC converter) and main drive inverter.
OBC is to charge the battery by rectifying and regulating the ac power in the power grid. The OBC power of mid-and-low-end models is mostly single-phase 3.7KW and 7.4KW, while some mid-and-high-end models have begun to use the three-phase 11kW and 22kW OBC power configuration.
DC/DC is the low-voltage power supply needed to convert the battery pack's voltage of several hundred volts into on-board appliances.
OBC and DC/DC are not high power but high frequency parts, and high frequency is the strength of SiC.
Using SiC devices on OBC can shorten charging time and reduce power loss; DC/DC using SiC devices, small volume, loss reduction.
For the main drive inverter, according to the above introduction, the use of SiC devices can help improve the range, and then reduce the cost by reducing the battery capacity