Silicon Carbide MOSFET

A vertical transistor carved from a crystal that exists in more than 200 polytypes, yet only one of them — 4H — punches hard enough to rewrite electric vehicle drivetrains.

A 4H-SiC MOSFET is a vertical n-channel power transistor that controls high-voltage, high-current circuits in power converters and inverters. Its role is to switch kilowatts of power on and off — hundreds of thousands of times per second — with minimum energy lost in the switching transition and minimum resistance when fully on. Compared with a silicon IGBT or silicon superjunction MOSFET doing the same job at the same blocking voltage, the SiC device switches roughly ten times faster and tolerates junction temperatures up to 175–200°C in qualified production parts. These properties directly reduce the size and weight of the magnetics (inductors, transformers) and heat sinks needed in a power supply, motor drive, or traction inverter.

The physics begin with the crystal: 4H-SiC has a bandgap of 3.26 eV compared with silicon's 1.12 eV, and a critical breakdown field of approximately 3 MV/cm versus silicon's 0.3 MV/cm. Because breakdown field determines how thin the blocking drift region can be for a given voltage rating, SiC drift regions are roughly ten times thinner than silicon equivalents at the same voltage. A thinner drift region has lower on-resistance for the same blocking capability — that is the fundamental advantage. In the vertical n-channel structure, an n-type SiC drift layer sits below a p-well, with the source contact above and the drain at the wafer back. Applying a positive gate voltage inverts the surface of the p-well just beneath the gate oxide, opening a thin inversion-layer channel through which electrons flow from source to drain. The oxide is thermally grown SiO₂, which creates a problematic SiC/SiO₂ interface with high trap densities, limiting channel electron mobility to roughly 10–30 cm²/V·s — far below the bulk value of 900 cm²/V·s. This interface quality problem, not the bulk SiC properties, is the principal engineering challenge. Despite it, on-resistance values of commercial 1200 V SiC MOSFETs are already ten or more times lower than silicon alternatives at the same blocking voltage rating.

In plain terms

Imagine a water slide where the guard rail is made of cardboard for ordinary riders — that's a silicon transistor. Now imagine the same slide but the rail is made of thick steel and can handle riders going ten times as fast without breaking. That steel rail is 4H-SiC. More voltage, more heat, more speed, same tiny size.

Also called: SiC MOSFET, 4H-SiC power MOSFET, SiC power switch, wide-bandgap power transistor.

Why it matters

In a 400 V or 800 V electric vehicle traction inverter, replacing silicon IGBTs with SiC MOSFETs reduces inverter switching losses by 50–70% at highway speeds, extending driving range by 5–10% for the same battery pack (Tesla Model 3 was the first mass-production example, with STMicroelectronics SiC modules).
Switching frequencies above 100 kHz are practical with low losses, shrinking the passive filter components (inductors, capacitors) in grid-tied solar inverters and onboard EV chargers by a factor of 3–10× compared with 10–20 kHz silicon designs.
Rated junction temperatures up to 175–200°C allow smaller or simpler cooling systems — a meaningful system-level cost reduction at kW scales.
Voltage ratings from 650 V to 10 kV (demonstrated) fill an application space — high-voltage motor drives, railway traction, medium-voltage grid converters — where silicon cannot compete at high switching frequency.

Where it lives

Tesla Model 3 traction inverter — STMicroelectronics 650 V SiC MOSFET modules; first mass-production EV inverter using SiC (2017)
Wolfspeed C2M0080120D — 1200 V, 80 mΩ discrete SiC MOSFET, widely used as engineering benchmark and in solar inverters
Infineon CoolSiC MOSFET 1200 V series — trench-gate SiC, in on-board chargers and industrial motor drives
Rohm SCT3022AL — 650 V SiC MOSFET in LLC resonant EV charger reference designs
ABB PSTX thyristor-free soft starters with SiC power stages for railway auxiliary converters
Semikron SKiN SiC modules — 1200 V, used in wind turbine full-power converters and industrial drives

Key numbers

Bandgap (4H-SiC): 3.26 eV (vs 1.12 eV for Si — raises avalanche threshold and permits high-temperature operation (Cooper et al. 2002))
Critical breakdown field: ~3 MV/cm (vs ~0.3 MV/cm for Si — ten times higher, directly enabling thin, low-resistance drift regions at high voltage)
Bulk electron mobility (4H-SiC, drift): ~900 cm²/V·s (Useful for drift region design; channel (inversion-layer) mobility is only 10–30 cm²/V·s due to SiC/SiO₂ interface traps)
Thermal conductivity: ~370–490 W/m·K (vs ~150 W/m·K for Si — enables higher power density without excessive junction temperatures)
Saturated drift velocity: ~2×10⁷ cm/s (Approximately 2× silicon — helps at high fields in the drift region)
Commercial voltage ratings: 650 V – 3.3 kV (production); 10 kV (demonstrated) (Fills the gap between silicon superjunction MOSFETs (<900 V) and high-voltage IGBTs)
Switching frequency: >100 kHz practical (vs 10–20 kHz for Si IGBTs at comparable voltage ratings — drives magnetics miniaturisation)

Surprising facts

The critical breakdown field of 4H-SiC (3 MV/cm) is ten times that of silicon — meaning a 1200 V SiC drift region is approximately 12 µm thick, while the silicon equivalent must be roughly 130 µm. That tenfold reduction in thickness directly translates to tenfold lower drift-region resistance for the same blocking voltage.
Silicon carbide exists in over 200 distinct polytypes — different stackings of the same Si-C bilayer — yet only 4H-SiC combines a large enough bandgap, high enough electron mobility, and adequate substrate availability for practical power devices.
The SiC/SiO₂ interface trap density is roughly 10–100× higher than at a Si/SiO₂ interface, which is why SiC channel mobility is only 10–30 cm²/V·s versus the 900 cm²/V·s bulk value. This single interface quality problem has driven years of nitric-oxide anneal and alternative gate dielectric research.
Large-diameter SiC substrate growth requires temperatures above 2000°C — the Lely sublimation technique (1955) was the first to produce usable crystals. Growing a 150 mm SiC boule takes several days in a furnace hotter than the surface of the Sun.

Open questions

Interface trap density that defeats bulk physics: The bulk electron mobility of 4H-SiC (900 cm²/V·s) should yield dramatically lower channel resistance than silicon, but the thermally grown SiO₂ gate dielectric introduces interface trap densities of 10¹²–10¹³ cm⁻²eV⁻¹ near the conduction band — ten to one-hundred times higher than at the Si/SiO₂ interface. These traps reduce the actual channel mobility to 10–30 cm²/V·s, erasing most of the bulk mobility advantage. Nitric oxide (NO) post-oxidation annealing partially passivates the traps and is now standard process, but the microscopic identity of the dominant trap species and the mechanism by which NO improves it remain subjects of active research after more than two decades of study.

A short history

Silicon carbide crystal growth began with Jan Czochralski-era attempts, but the modern era starts with Jan Antony Lely's 1955 sublimation technique, which produced the first reproducible SiC platelets at Philips Research. Modified by Yuri Tairov and Valery Tsvetkov in 1978 with a seed-crystal approach, this became the basis for all commercial boule growth. Cree Inc. was founded in 1987 at North Carolina State University specifically to commercialise SiC, initially for blue LED substrates. The SiC MOSFET itself was demonstrated in research through the 1990s, with the principal obstacles being SiO₂ gate oxide quality and SiC/SiO₂ interface trap density. Cree (now Wolfspeed) introduced the first commercially qualified 1200 V SiC MOSFET in 2011. Adoption was slow until 2017, when Tesla integrated STMicroelectronics SiC modules into the Model 3 main traction inverter — the first mass-production EV to do so. That design validation triggered rapid industry uptake: by 2023 virtually every major automotive OEM had SiC inverter programmes, and the 650 V and 1200 V SiC MOSFET had become the dominant technology for power conversion above 650 V in new designs.

Sources

Cooper et al. — '4H-SiC MOSFETs and Their Impact on Power Electronics', IEEE Trans. Electron Devices 49, 658–664 (2002). DOI: 10.1109/16.992866 (https://doi.org/10.1109/16.992866)
Kimoto T. & Cooper J.A. — 'Fundamentals of Silicon Carbide Technology' (Wiley-IEEE, 2014). DOI: 10.1002/9781118313534 (https://onlinelibrary.wiley.com/doi/book/10.1002/9781118313534)
Wolfspeed C2M0080120D SiC MOSFET product datasheet — 1200 V, 80 mΩ, TO-247-3 and D2PAK (https://www.wolfspeed.com/products/power/sic-mosfets/)
Ryu S.-H. et al. — '10 kV, 123 mΩ-cm² 4H-SiC Power DMOSFETs', IEEE Electron Device Lett. 25, 556–558 (2004). DOI: 10.1109/LED.2004.831354 (https://doi.org/10.1109/LED.2004.831354)
STMicroelectronics — Tesla Model 3 SiC inverter technical brief, AN5252 application note (https://www.st.com/content/dam/AME/2019/developers-conference-2019/presentations/STDevCon19_3.6_Using-SiC-in-EVs.pdf)