If something uses electricity it is likely that it must also meet energy efficiency standards.
The choice of power semiconductors will be fundamental to meeting those standards.
SiC is enabling advances in EV chargingSilicon has long been the default material for almost every type of device, from logic to memory to power ICs to diodes. More recently, other materials, including silicon carbide (SiC) and gallium nitride (GaN), have gained traction in power applications. The reason is silicon has several limitations when it comes to delivering higher power efficiently.
What makes SiC and GaN more appropriate for high-power and high frequency power applications? They are wide bandgap (WBG) semiconductors, which gives them several desirable electrical and thermal properties for power applications. This has led to the development of many different SiC-based power components, including Schottky diodes and PiN diodes, as well as metal–oxide–semiconductor field-effect transistors (MOSFETs), junction FETs (JFETs), static induction transistors (SITs) and bipolar junction transistors (BJTs).
Material properties of silicon carbide
SiC and GaN have wider bandgaps than silicon. This means electrons must gain more energy before moving to a level where they become conductive.
In fact, there are several different forms of SiC, known as ‘polytypes’, with their atoms arranged differently. These include 4H-SiC, 6H-SiC, and 3C-SiC forms – but the only one that is widely used in power semiconductors is the ‘4H’ variety, because of its electrical, thermal, and mechanical properties. While similar, 6H-SiC tends to find more uses in light-emitting applications such as high-brightness LEDs.
Compared to silicon, this wide bandgap gives SiC some key advantages at a material level, including:
- greater electric breakdown field, of 3 MV/cm, around ten times larger than silicon's breakdown field of 0.3 MV/cm
- higher thermal conductivity, of 5 W/cmK, compared to 1.5 W/cmK for silicon
Below, we explain the impact of these advantages at a device, board, and system level.
Device-level properties of SiC semiconductors
Compared to silicon devices, SiC components have several appealing electrical properties. First, their drain-to-source on-resistance, or RDS(on), is lower than silicon, which enables lower conduction resistance. This means SiC devices dissipate less heat and have lower power losses when conducting. This makes them more suitable for high current applications. The RDS(on) of SiC also increases less with temperature than silicon does.
SiC also has advantages over silicon when comparing thermal properties. The larger bandgap of SiC means more thermal energy is needed to move electrons across the bandgap than in silicon components.
Other advantages of SiC at a device level include:
- faster reverse recovery, reducing losses
- shorter switch-off times
- lower capacitance, helping to enable faster switching with lower losses
- low gate charge, reducing losses and hence power consumption
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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 OVERVIEWBoard-level advantages of SiC power devices
At the board level, these properties translate into some important benefits for SiC. Firstly, SiC components offer much higher switching frequencies than silicon when operating at high temperatures and voltages.
The higher breakdown voltage of SiC components enables higher operating voltages and hence higher power operation than silicon alternatives, with SiC MOSFETs rated at up to 3.3 kV. SiC devices can also be designed for higher currents than silicon components (with current density up to five times greater), thus enabling high power operation.
The thermal advantages mentioned above, combined with SiC’s greater thermal conductivity, means that SiC devices can be used at higher temperatures than silicon — up to around 150ºC, compared to up to about 100ºC.
While we have been mostly comparing SiC to silicon, how does it stack up in comparison to GaN? The main advantages of SiC are its ability to operate at higher voltages and higher temperatures than GaN.
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System-level advantages of SiC semiconductors
At a system level, one of the key advantages of higher efficiency is reduced energy losses. This lowers both the amount (and cost) of energy used and the need for energy storage. Higher efficiency benefits any application directly impacted by operating costs, such as electric vehicle charging, industrial power systems, and telecoms.
Greater efficiency also means lower heat dissipation, simplifying thermal management. This reduces the need for large heatsinks and cooling infrastructure, allowing for more compact power system designs. In applications where space and cooling constraints are critical, this translates to lower costs and improved reliability.
The high switching frequencies of SiC devices enable the use of smaller inductors and capacitors, allowing for higher power density and more compact system designs. This is particularly valuable in applications where size and weight are constraints, such as DC chargers and on-board inverters, and PV inverters.
Challenges in adoption of SiC technologies
Moving from silicon to SiC can bring substantial benefits, but SiC components are not drop-in replacements – so there’s design effort required to understand their requirements, and how your system might need to be re-designed for the new SiC world.
Another hurdle is cost. While SiC device vendors have been driving down costs, for example with the shift to larger 200mm wafers, there is still a price premium over silicon. For certain high-power and high-frequency applications, such as fast electric vehicle battery chargers, SiC ICs will be the only practical choice, regardless of price.
Silicon also has a long-term track record of reliable operation – although SiC MOSFETs are now widely considered a mature technology, with years of testing and excellent, proven reliability.
Making the right choice
As this article has explained, SiC has much to offer the power designer, but it’s not the perfect solution for every situation. In practice, the specific requirements of your application will determine whether SiC is best for you, or whether silicon or GaN fit the bill.
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