In applications such as inverters, motor drives and battery chargers, silicon carbide (SiC) devices offer advantages such as higher power density, reduced cooling requirements and lower overall system cost.

Although an SiC device costs more than its silicon counterpart, the system level benefits, particularly at 1,200V, more than compensate for the higher device cost. The benefits compared to silicon are marginal at or below 600V. An SiC die needs specially designed packaging and gate drivers to reap the advantages.

Advantages of SiC over silicon

Typically, the energy lost by SiC during the reverse recovery phase is just 1% of the energy lost by silicon. The virtual absence of a tail current allows a faster turn‑off and dramatically lower losses. Since there is less energy to dissipate, an SiC device can switch at higher frequencies and improve efficiency.

The higher efficiency, smaller size and lower weight of SiC can create a higher-rated solution or a smaller design with reduced cooling requirements.

The performance of silicon worsens over higher temperatures, whereas SiC is much more stable. A silicon device is usually over-specified at room temperature to maintain specification at higher temperatures. Typically, an SiC device with half the current rating will perform the same job as a silicon IGBT because SiC is much more stable over higher temperatures and doesn’t need significant derating.

SiC operates at above 10kV, significantly above what can currently be used. SiC devices rated at 1,200V and 1,700V are available. With issues such as arcing, creepage and clearance, packaging has become the limitation – not the semiconductor technology.

Lower losses

The major sources of energy loss in an SiC module are conduction losses. As a wide bandgap material, SiC has a low gate charge, which means that SiC needs far less energy to make the device switch.

Diode switching losses are virtually eliminated because of the dramatic improvement in reverse recovery energy and tail current. Switch conduction losses are resistive and consequently are similar in both technologies. Next-generation SiC processes promise further improvement.

Higher frequencies mean reduced size and weight of the magnetics because the values of components in the transformer LC filter become significantly lower.

SiC also delivers 10x the mean time to failure (MTTF) of silicon and is 30x less sensitive to radiation and single event failure. However, SiC has a lower short circuit tolerance and hence needs a fast-acting gate driver.

A standard, hard, turn off transition (left) and a softer stepped transition, which will reduce the di/dt