Ideally, Silicon carbide MOSFET is superior than Silicon MOSFET on below areas:
- Silicon carbide (SiC) has wider band gap than Silicon (Si) (~3 eV versus ~1.1 eV). This means it can handle higher electric fields and temperatures.
- Sic has superior thermal performance, it has higher melting point. This equates to a higher power density.
- SiC is more efficient than Si due to lower losses attributed to lower RDSon and dynamic parameters.
- At higher voltage applications, SiC able to maintain lower RDSon and dynamic parameters and Si.
Above idealities are not always true to all scenarios and applications. Generally, no doubt that SiC excels in today’s power electronics. However, Si MOSFET is not going to be EOL soon enough since there are some applications and scenarios that economically effective when using Si solution.
Studying High Voltage Application
To investigate and demonstrate both Si and SiC performance at high voltage, we conducted a study. The study focused in the 1.2kV N-channel MOSFET from 10A to 20A current range. This study was done using Mouser Electronics data. Mouser is one of the most popular online stores for electronics. We made a custom filter in Mouser and get below data.
Supply Availability
There are 25 parts available for SiC while 22 parts available for Si. Just looking into this parameter, there is no advantage to select SiC over Si. Both parts are available.
Temperature Rating
From the study, all the 25 SiC parts are rated 175’C while none of the 22 Si parts are rated 175’C. In terms of RDSon, SiC is very much superior compared to Si.
RDSon
In SMPS, it is not only the voltage rating is important. There are other factors such as RDSon and total gate charge. Below is the RDSon comparison between SiC and Si from the sample size experimented in Mouser. The data won’t lie, SiC has very low RDSon than SiC MOSFETs.
Total Gate Charge
Below is the comparison of the total gate charge between SiC and Si based on the 10A to 20A current range for 1.2kV MOSFETs in Mouser. It is clearly indicated in the graph that SiC is very superior to Si. Total gate charge is one of the big contributors of switching losses. To learn more about this, read How to Compute MOSFET Switching Losses.
Key Takeaways at High Voltage Applications
- At 1200V, particularly at 10 to 20 amps range, both Si and SiC has abundant supply. Both can be used as long as meeting specific design requirements.
- If the design requires a higher power density (more power in a small footprint), SiC is the ultimate choice. This is because with SiC, the device actual junction temperatures or internal hotspots of the PSU can be pushed further without damaging the MOSFETs in courtesy of higher temperature limits.
- The challenge in high voltage application is to maintain a lower conduction loss. Conduction loss is the power dissipation due to the MOSFET RDSon. Conduction loss is a main contributing factor to overall efficiency. It must be small enough to attain high efficiency. The perfect choice to address this challenge and attain high efficiency while staying at high voltage application is to select a SiC MOSFET.
- Another key factor in obtaining high efficiency is the total gate charge. The lower the total gate charge the better the efficiency. SiC have low total gate charge and Si, thus it is the best choice of obtaining high efficiency while at high voltage application.
- It is not literally the voltage is being after for SiC but the availability of options to superior RDSon, total gate charge and high operating temperature while staying at high voltage.
Studying Low Voltage Application
We conducted another study (still using Mouser) and this time at 650V, 6 amps to 30 amps current range.
Supply Availability
From the table, it is crystal clear that Si MOSFET supply is tremendous. With this, it is expected that Si MOSFET is relatively cheap compared to SiC at the same voltage and current ratings.
Temperature Rating
The data shows that there is no device that is rated to 175’C for Si but there are 16 out of 23 (~70%). The SiC part slightly edge the Si for this aspect.
RDSon
At 650V application, 6 amps to 30 amps range, Si MOSFET has slightly better RDSon. See the graph below. The x-axis is the number of devices while the y-axis is the RDSon in ohms. It is not absolutely better because some of the SiC parts have lower RDSon than Si.
Total Gate Charge
At 650V, 6 amps to 30 amps current range, Si MOSFET has better total gate charge. This is way better because there are only few intersections when both lines are overlapped.
Key Takeaways at Low Voltage Applications
- At low voltage application (650V on the conducted study), Si MOSFET supply chain is extremely abundant. Because of this, the price is very cheap compared to the SiC device. Thus, this is the first choice for availability and cost are concern.
- At 650V application, SiC device still has options that reaching 175’C.
- At 650V application, Si MOSFET is slightly better than SiC in terms of RDSon.
- At 650V application, Si MOSFET is significantly better than SiC in terms of total gate charge.
- In general, at low voltage application, SiC MOSFET is not a good choice at all. Though it has options that can withstand 175’C but since it has higher RDSon and total gate gate charge than Si, the temperature advantage is cancelled out. Si MOSFET is generally a good choice at low voltage application satisfying aspects like supply chain, costs and performance.
Comparison between 650V and 1200V, 6 amps to 30 amps Current Rating
Silicon carbide (SiC) MOSFET is not overall better than Silicon (Si) MOSFET. This is explained in the study conducted at 650V application wherein Si MOSFET is a better choice to meet key performance indicators.
Based on the study conducted, SiC is best at high voltage application and it is generally the overall winner at high voltage application.
The comparisons below lamented these claims.
Realization for Both Silicon Carbide and Silicon MOSFET
- In general, SiC MOSFET is the best choice at higher voltage application. The study conducted is 1200V wherein all the aspects are leaning towards SiC favor. This could be applied down to 800V applications.
- Another generalization is that at lower voltage application (at 650V particularly), Si MOSFET is still the king. Thus, Si will not be going EOL soon.
- There are still options for Si MOSFET at higher voltage application (1200V in the study). However, it is not a good choice if the requirement is strict for power density, temperature and efficiency.
- SiC’s greatest advantage is often related to its higher voltage capability. This is not literally correct because there are also options for Si at higher voltage. However, the statement is generally accepted and adopted because at higher voltage application, SiC MOSFET is able to maintain a low RDSon, low total gate charge and higher thermal capability compared to Si MOSFET.
- SiC is naturally able to handle high operating temperatures. Based on the study, there are lot of options for SiC MOSFET at 1200V category and there is none for the Si MOSFET based on the sample size defined. High operation temperature is critical in obtaining high power density SMPS because you can extend your hotspot temperature limit.
- The temperature advantage is a big factor for SiC MOSFET. If using Si MOSFET, the temperature limit could be set to 130’C for a 150’C junction temperature rated Si MOSFET. But when using SiC with a junction temperature of 175, the limit can be pushed to 150’C. With this, the power can be pushed further while maintaining the same physical size.
- At higher voltage application, SiC has lower RDSon and total gate charge compared to Si. This will make the conduction loss and switching loss lower and result in lower temperature, thus can further push the power.