SiC has many exceptional properties that make it an excellent material for power devices like those found in new smart electric vehicles and inverters, offering lower on-resistance and switching losses than silicon transistors [1].
This article highlights recent progress made towards developing 1.2 kV-class SiC MOSFETs, as well as key performance issues associated with their use.
Low On-State Loss
Silicon Carbide (SiC) is the next-generation material for power devices. Offering higher operating voltage, lower losses and greater reliability compared to silicon-based semiconductors, SiC MOSFETs have become the go-to choice in power conversion applications such as automotive traction inverters, uninterruptible power supplies (UPSs) and PV inverters.
SiC power mosfets boast low on-state losses that allow it to operate at higher switching frequencies than bipolar versions, thus reducing overall system power losses and overall system power losses. Furthermore, SiC MOSFETs feature lower RDS(on) than bipolar counterparts, making them less temperature sensitive while requiring less gate drive current than traditional silicon MOSFETs to attain an on-state drain current that reduces total system losses further.
However, SiC MOSFETs exhibit higher turn-off losses than bipolar transistors and their impact on system losses isn’t linear with duty ratio. Therefore it is crucial that designers are familiar with these dynamics to design reliable high-speed power conversion systems.
Reaching a harmonious equilibrium among dynamic parameters is essential to high-speed operation and minimising switching losses. Careful PCB layout and implementation of protection circuitry help eliminate parasitic components which contribute to overvoltage spikes or other fault conditions, protecting power converters from damage while increasing system efficiency. UnitedSiC’s 1700 V LV SiC MOSFET UF3SC120009K4S has been specifically engineered for high power DC-DC converters to maximize performance and reliability.
High Current Density
Silicon Carbide MOSFETs feature higher current densities than their silicon counterparts, leading to smaller components and reduced system loss, thus increasing efficiency in power conversion systems, higher switching frequencies and smaller designs that allow cooler components (inductors, capacitors and transformers), as well as providing substantial cost savings. This results in greater efficiency as well as reduced system losses – leading to greater system efficiency as a whole and potential cost savings as a result of their use.
SiC devices feature higher current density as well as lower on-resistance and breakdown voltage than their silicon equivalents, making them suitable for use in applications ranging from UPSs and photovoltaic inverters to electric vehicles.
High current density and fast switching speeds are enabled by the fact that SiC power MOSFETs feature lower drain-source resistances compared to similar-sized silicon devices due to thinner n-layers; this lowers total drift layer resistance by approximately 1000 times, leading to reduced on resistances and subsequent decreases in on resistance.
SiC power MOSFETs’ higher switching frequencies also aid their performance by minimizing parasitic effects, like impact ionization leakage current and band-to-band tunneling leakage current, which reduces power loss and increases efficiency across a wider temperature range. They tend to be less sensitive to temperature changes; thus enabling them to operate at lower temperatures while still offering similar reliability as their silicon counterparts.
High Voltage Capability
SiC power MOSFETs feature higher blocking voltage compared to their silicon counterparts, making them an excellent choice for high-voltage applications such as IGBT replacement in the 5-8kV range. Their on-resistance is considerably lower – typically between 1-3mOcm2 for 1kV class MOSFETs with typical channel mobility of 20 cm2/Vs (Source: Yole).
High blocking voltage comes at the expense of short circuit withstand capability; to prevent device/system failure it’s essential that 1200-V SiC power MOSFETs can withstand short-circuit conditions without thermal breaks and provide adequate short-circuit withstand capacity.
To achieve this goal, high-quality SiC epitaxial layers need to be constructed from clean and crystalline wafers, using sophisticated process technologies, structure designs and packaging techniques. Furthermore, defect density must remain low to ensure optimal performance and reliability of SiC materials.
GeneSiC has successfully achieved their goals and now provides high-performance SiC power MOSFET modules and bare die for use in mission-critical applications like electric vehicles, fast chargers, railways, industrial drives, solar energy and renewable energy systems. Their advanced technology ensures industry-leading avalanche ratings, superior RDS(ON) switching losses and temperature invariant switching losses for superior efficiency and reliability across a broad range of power conversion applications.
Fast Switching
Power MOSFETs are voltage-controlled devices that turn on and off in response to a gate signal. A positive voltage applied to the gate generates an electric field which attracts electrons and forms a conductive path between source and drain terminals, placing the device into its “on” state. Conversely, applying negative gate voltage turns off this field, blocking current flow, thus placing it into its “off” state.
SiC power mosfets offer low on-state loss for fast switching, increasing efficiency in server and uninterruptible power supplies (UPS) applications. Their fast switching speed also enables faster slew rates in DC-to-DC converters and photovoltaic inverters.
SiC power MOSFETs also boast superior RDSon stability compared to silicon power MOSFETs, making it easier for power circuits to work in extreme temperatures.
Sic power mosfets offer additional advantages when combined with gate driver ICs. For instance, Texas Instrument’s UCC217xx single-channel isolated gate drivers for IGBT and SiC MOSFET power switches offer outstanding gate drive performance, high-speed protection features and strong sink capability to safeguard them against Miller turn-on effects.
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