SiC devices are made by growing them on a substrate, or wafer, using a process called epitaxy. AI and supercomputers may grab the headlines, but power electronics is the driving force of today’s technological advancements. In fact, there’s a booming demand for efficient, robust power semiconductors that can handle the needs of data centres, electric vehicles (EVs), and countless other applications.
Traditionally, silicon has been the material of choice — but power systems design is being transformed by the new kid on the block: silicon carbide (SiC). Silicon carbide is a wide bandgap (WBG) semiconductor, which means it has a greater bandgap than silicon and higher energy electrons that cross this bandgap.
The practical result of having a wider bandgap is properties that become extremely useful for power electronics, including reduced conduction and switching losses, allowing for faster switching and better efficiency. Due to its wide bandgap, SiC can also operate at temperatures and voltages higher than silicon. Correspondingly, a SiC power IC delivers the same performance as a silicon power IC in a smaller and lighter package.
In this article, we provide an overview of SiC and its advantages for power electronics applications.
Fabrication of SiC substrates
SiC devices are made by growing them on a substrate, or wafer, using a process called epitaxy. The substrate can be silicon, or the SiC devices can be made on SiC wafers. Just like silicon, SiC can be doped with different elements to affect the electrical properties of the resulting devices. SiC wafers are also used as substrates for gallium nitride (GaN) devices — GaN being another WBG semiconductor used extensively in power electronics.
Today, the most common size of SiC wafers is 150mm diameter. While 200mm wafers have been announced and could help drive economies of scale and increase production quantities, they have not yet entered volume production. By way of contrast, silicon fabs commonly use 300mm wafers. The difference between them gives silicon fabs a significant advantage when it comes to throughput, and therefore the cost, of silicon devices.
Types of SiC power devices
Figure 1: Cross section of SiC MOSFET with equivalent circuit
(Source: everythingpe.com/community/what-are-silicon-carbide-sic-mosfets)
SiC is used in a variety of different devices in power applications. This includes Schottky diodes and PiN diodes, and both types of field-effect transistor (FET): the metal–oxide–semiconductor FET (MOSFET), which is the most common, as well as the junction FET (JFET). SiC is also well-suited to use in static induction transistors (SITs) and bipolar junction transistors (BJTs).
Figure 1 shows the structure of perhaps the most important SiC component, the SiC MOSFET. This is similar to traditional silicon MOSFETs, with the three main parts of source, gate, and drain. The MOSFET is controlled by the voltage applied to the gate terminal, which determines what current can flow between the source and drain terminals.
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Advantages of SiC power devices
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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 OVERVIEWFor power electronics, the benchmark has been set by silicon transistors, and most often insulated gate bipolar transistors (IGBTs). Compared to silicon, their larger bandgap means SiC devices have a higher breakdown voltage, ten times greater than silicon. This is because a greater electric field is needed to produce electrons that can carry charge.
One of the key advantages of SiC devices is their higher efficiency, related to higher switching frequencies and lower on-resistance (RDS(on)), hence lower conduction losses. The on-resistance also varies less with temperature than silicon devices.
SiC devices have much better thermal conductivity than silicon — about three times greater. This helps exploit the potential to operate SiC at high temperatures and higher switching speeds, leading to greater power density.
For more information, see the following article: SiC semiconductor advantages.
Applications of SiC semiconductors in power electronics
These advantages mean that SiC is a good choice where efficiency is a priority, such as in EVs, EV chargers, and data centre power systems, and where high voltages and temperatures are required, such as some industrial and motor drive applications.
Another major application is in renewable energy, such as solar and wind, where switching in inverters at voltages up to 800 V may be required. In these applications, SiC’s better efficiency means it typically has lower losses compared to an equivalent silicon IGBT device.
For more information, see the following article: SiC semiconductor applications.
The choice of packaging
SiC devices require special packaging. Generally, the same packages are used by more than one supplier, so you aren’t reliant on a single source.
For example, ST offers SiC MOSFETs in the HU3PAK package, which has the same footprint, thickness, and is pin-compatible with the BPAK package used for silicon IGBTs. HU3PAK is designed to be surface-mounted on a PCB, with its top side connected to an external heat sink. Other suppliers, such as onsemi, are also developing with new products in this package.
Another package used for SiC MOSFETs is TO-LL (leadless), as used by ST and onsemi, which provides a good balance between thermal management, current capability, and PCB space. Nexperia, Renesas, and Navitas also have products in this package.
Finally, the four-pin TO247-4 package maximizes switching performance. Suppliers using this package for SiC MOSFETs include ST, onsemi, Nexperia, and Rohm, while Navitas and Renesas are also working on similar options.
Design considerations
When adopting SiC technology, there are several areas that deserve consideration. First, you can ask an Avnet Silica power expert to check there is a SiC device that matches the voltage and current ratings of your application, one that can efficiently handle the switching frequency you require. The higher switching frequencies of SiC also mean there are parasitic elements that need to be thought about.
Then, it’s important to remember the gate driver must provide the appropriate voltage and current. Another issue to consider is thermal management, with thermal interface materials and heat sinks capable of dealing with any heat generated. Although SiC can operate at high temperatures, thermal stress will still reduce the component’s lifetime.
Also, with a SiC MOSFET, you need to consider the reliability of the SiC MOSFET’s body diode. Its performance and stability can impact the reliability of the MOSFET and your overall power system design.
Challenges in adoption of wide bandgap technology
SiC devices have multiple advantages over silicon, and typically a higher cost. The higher price is largely because processing SiC is still more complex. This cost difference is being addressed by vendors moving to larger wafer sizes and increasing production volumes.
Reliability has been a concern in the past but SiC MOSFETs are now widely considered a mature technology with excellent reliability, proven by extensive testing and long-term use in the field. Avnet Silica is happy to provide reliability data.
The future for SiC semiconductors in power electronics
With the cost of SiC devices coming down by improvements in production, the range of possible applications continues to broaden. SiC devices are also the technology of choice in some large, high-growth markets – particularly the EV and renewable sectors, where their ability to handle high voltages and temperatures is invaluable.
The market for SiC in power electronics is growing significantly, and is projected to reach US$10 billion by 2029, capturing 28.6% of the global market.1
Will SiC replace silicon completely? No, at least not in the short- to medium-term. Silicon’s proven track record and lower cost mean it has many more years to go as a major technology in power electronics.
Making the right choice for your application
Choosing the right technology and components always involves trade-offs. With SiC bringing new options for power systems, you need to compare silicon and SiC, as well as other choices such as gallium nitride (GaN). This is where Avnet Silica’s expert advice can help you pick the right path.
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