Silicon Carbide: Understanding The Value Proposition

In the ECCE 2015 plenary presentation entitled, "SiC Power Devices: Changing the Dynamics of Power Circuits from 1 to 30 kV," power electronics engineers will learn about current and future applications for SiC power semiconductors spanning 1kV to 30kV, in addition to the performance and cost advantages of SiC MOSFETs with ratings spanning 900V to 15kV and SiC IGBTs spanning ~10kV to 27kV.

The performance advantages of SiC over silicon are well understood, and now that SiC devices are commercially available, the most common concern raised by design engineers is that it's more expensive than silicon, which is true. However, a thorough examination of the benefits of SiC over silicon will demonstrate that this is not a component-to-component comparison.

The cost of SiC devices is justified by their performance at the system level, which is reflected in the system cost, rather than the component cost. In a typical application, SiC devices make systems less expensive by enabling them to operate at higher frequencies and with smaller magnetics and simplified designs; for example, going from multi-level topologies down to less complex two-level designs. Design complexities have been developed around the limitations of silicon IGBT devices in terms of speed and thermal load. These complexities aren't necessary with silicon carbide. So, design engineers should concentrate on the overall system savings that are possible with SiC.

This message is not only for design engineers, but for other corporate decision makers, including purchasing agents, who often focus exclusively on a component-to-component cost comparison without evaluating the overall cost reduction or added value to the application. This change of focus can only come about when the entire design and supply chain knows about the value proposition of silicon carbide.

Regarding future applications for SiC power devices, it's important to recognize that, while SiC devices are currently only available with operating voltages up to 1700V, SiC devices rated for 3.3kV, 6.5kV, and 10kV are being developed for commercialization. Although these higher voltage devices are not yet commercially available, it's definitely time for system designers to start thinking about their potential in higher power applications, such as motor drives, traction control, and grid-level power management.

Engineers familiar with the performance tradeoffs between silicon MOSFETs and IGBTs may be interested to learn that there are similar tradeoffs with higher-voltage SiC MOSFETs and the SiC IGBTs that are now in development. Similar to the "crossover point" observed in silicon devices, somewhere between 600V and 1200V, the crossover point between SiC MOSFETs and SiC IGBTs is typically somewhere between 10kV and 15kV. Voltages above that threshold will require a bipolar device in SiC (i.e., an IGBT).

Of course, there are other considerations when selecting such high voltage switching devices, some of which will be featured in an NC State University paper being presented as part of the ECCE technical program later in the conference.