What is a wide bandgap?
Wide bandgap (WBG) semiconductors are steadily becoming more common in power electronics applications, replacing existing silicon alternatives. They have several key advantages over silicon — notably, their ability to handle greater switching frequencies, which can improve conversion efficiency, and to operate at higher temperatures and higher voltages.
That’s the elevator pitch, but what actually is a wide bandgap?
Let’s have a quick theory reminder. Quantum physics tells us electrons in a solid exist in specific energy states, and that when they absorb electromagnetic energy (such as heat or light) they can move to a higher energy state.
Figure 1: Band gaps (Source: based on diagram at https://www.powerelectronicsnews.com/wide-bandgap-wbg-semiconductors/)
The point here is that our WBG semiconductors have, you guessed it, a wider bandgap than regular semiconductors like silicon. This wide bandgap is the reason for their specific electrical and thermal properties. Figure 1 on the left side shows this — as well as also how the two bands overlap in conductors, such as metals.
The two most commonly used WBG semiconductor materials in power electronics are silicon carbide (SiC) and gallium nitride (GaN). The table on the right side shows some of their key properties, compared to silicon — you can see the larger band gap, and also other properties that affect the semiconductors’ behaviour.
One more complication to mention here: SiC can exist in different physical structures of its atoms, called ‘polymorphs’, which have different properties. We’ve included the polymorph called ‘4H-SiC’ in the table as this is the most used in power electronics, due to its excellent electrical, thermal, and mechanical characteristics.1
Types of wide bandgap power devices
We’ll focus on the two main WBG materials used in power electronics: SiC and GaN. Compared to silicon, they typically offer higher efficiency and other performance benefits — more on this later. These properties make them attractive for multiple types of semiconductor power devices, including:
- SiC MOSFETs
- SiC Schottky diodes
- SiC PIN diodes
- SiC JFET / SIT
- SiC BJT
- GaN FETs
(Notes: – based on table at https://www.st.com/content/dam/AME/2019/technology-tour-2019/chicago/presentations/T1S8_Schaumburg_SiC_J.Fedison.pdf Note: presentation is from 2019)Technology
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With the ongoing shift to renewable energy and the electrification of transport and industry, the demand for higher power and greater energy efficiency in electronics is increasing. Wide bandgap technologies including SiC and GaN bring many advantages.
WBG OVERVIEWAdvantages of wide bandgap power devices
As mentioned earlier, one of the key advantages of WBG devices is their higher efficiency, which is related to higher switching frequencies. This means they are attractive for applications where every possible watt of power must be available for use, such as in electric vehicles (EVs) — squeezing a few percent greater efficiency out of the onboard power conversion electronics can noticeably improve an EV’s range, which is a big competitive advantage for carmakers. High efficiency is also an important factor in solar / PV applications.
GaN’s high switching frequencies also mean the inductors and capacitors used in a power supply can be much smaller. This weight and space saving is attractive in compact and portable applications, such as power supplies for laptops and other consumer electronics.
SiC, on the other hand, excels where high voltages and temperatures are required, such as in some industrial and motor drive applications. As a rule of thumb, silicon IGBTs may be the best option when the switching frequency is about 20 kHz, and/or the power level is above 3 kW, while higher frequencies and lower powers may indicate a SiC MOSFET is a better choice.
For a more extensive list, see the following article: wide bandgap advantages.
Applications of wide bandgap semiconductors in power electronics
Let’s take a more specific look at some examples of how WBG devices lend themselves to particular applications and across industry sectors.
- Automotive:
- EV powertrain
- traction inverter
- onboard charger
- bi-directional
- onboard charger onboard DC/DC converter
- fast charging system
- EV charging:
- Off board charger
- DC fast charging
- Wireless charging
- Industrial:
- Power supplies
- Motor drivers
- Uninterruptible power supplies
- Renewable and green energy:
- Solar inverters
- Wind turbines
- Large-scale energy storage
- Home energy storage
- Heat pumps
- Microgrids
- Data centres:
- Data centre and server power supplies
- DC/DC conversion
- Backup power
- Consumer:
- Wall chargers (AC/DC conversion)
- USB-C
- Wireless charging
- Telecoms:
- Power supplies
- Base stations
- 5G
For more detail on these applications, see the following article: wide bandgap applications.
Design considerations
What do you need to think about when adopting WBG technologies?
The choice of gate driver for a SiC or GaN device needs careful consideration, depending on the application and the circuit design used. In many cases, a dedicated driver can provide the best results, including generating the optimal gate drive voltage and provide desaturation detection which, if left undetected, could result in failure.
For high switching frequencies, EMI is another potential issue, with suitable filtering needed to avoid problems from emissions. You need to carefully consider your PCB layout and think about parasitic capacitance and inductance.
The high power density of WBG devices creates new challenges in thermal management. While SiC can operate effectively over a wide temperature range, the small size of WBG power systems means that heat dissipation should be considered.
Thermal stress is one of the main factors that impact the reliability of WBG devices. Other issues that affect reliability include, for SiC MOSFETs, the degradation of the device’s body diode.
Challenges in adoption of wide bandgap technology
Silicon devices still tend to have lower costs than WBG alternatives, which can be the most important criterion in some use cases. Fabricating WBG devices requires complex processes and specialised equipment, which pushes costs up. It also requires particular substrates, which may be in limited supply.
As you might expect, device vendors are working at speed to minimise this price premium. This includes shifting production of GaN devices from 200mm to 300mm wafers, which aims to reduce production costs.
Another factor to consider is reliability, with silicon’s proven long-term track record giving it an edge over newer WBG devices. This difference is being addressed, with SiC MOSFETs now widely considered a mature technology with extensive testing and excellent reliability.
The future for SiC and GaN in power electronics
WBG devices have already come a long way over the last few years, but the future holds the promise of much more progress. Improvements in manufacturing continue to drive down WBG costs, and there is evidence that reliability is increasing to levels that make WBGs suitable for use in automotive and other applications with strict quality standards. For example, onsemi performs comprehensive verification and validation tests on SiC products for automotive, including reliability testing at 100% of rated voltage and an elevated temperature of 175°C.2
There are huge opportunities for growth in WBG adoption, particularly in expanding markets such as EVs where the take-up of WBGs is likely to be fastest. EVs are a good example of an application where power efficiency is of critical priority, so the cost premium of WBGs over silicon is not a problem. As well as the vehicles themselves, WBGs are the technology of choice in the charging network, which is growing rapidly — with at least six million new chargers required by 2030, in just the EU.3
High-power applications, such as renewable energy production, are another strong growth area for WBGs, with SiC’s ability to handle higher voltages than silicon making it an appealing option.4
In the near future, cost reductions will also make WBG more appealing for other applications where they are currently seen as too expensive, such as low-cost consumer electronics. But don’t write off silicon just yet — it will continue to be the dominant material in power electronics for years to come, as a proven, reliable option.
Making the right choice for your application
Are WBGs right for you, and should you go for SiC or GaN? There is a lot to consider, ultimately your application and its requirements will determine the right choice. Avnet Silica’s FAEs and power engineers can provide the expert assistance you may need and can help you make the right decision for your power electronics application.
References
1. https://www.preciseceramic.com/blog/4h-sic-and-6h-sic-differences-how-to-choose.html
3. https://my.avnet.com/silica/resources/article/power-trends-si-sic-gan/
4. https://www.powerelectronicsnews.com/wide-bandgap-wbg-semiconductors/
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