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May 4, 2017

For SiC, "Someday" Is Today

Kevin Speer, PhD
Global Manager, Tech Strategy & Bus Dev, Littelfuse, Inc.

Power Channels: Energy Efficiency, Power Components

What do you see as the biggest barriers for circuit designers that want to use SiC in their power converter products?

At the component level, the biggest barriers are affordability, availability, and reliability. The expectation is that the principle of economies of scale will allow prices to fall substantially; as customer demand surges and broadens across multiple vertical markets, the raw material costs, which represent most of the cost of the end devices, will start to drop. Consequently, the price of components will also go down. Availability is changing constantly, with new entrants to the SiC supply base showing up at nearly every tradeshow. Obviously, some of those suppliers won't stick with it, but the stronger brands, such as Littelfuse, will be around for the long haul. Silicon carbide is not the only semiconductor technology that has had to go through a rigorous qualification process to demonstrate its reliability to potential customers. Fortunately, today there are multiple SiC MOSFET and MPS diode vendors offering products with reliability that's suitable for the majority of industrial applications.

Where do you see SiC technology five years from now?

I see SiC technology surging in the multi-chip or "module" format. However, SiC-based modules will likely look very different from today's silicon-based IGBT modules in several ways. They'll have dramatically reduced interconnect length and the layout symmetry will be better organized to ensure identical control paths to the individual chips. I also think we'll see some innovative cooling methods that remove multiple thermal interfaces. We might also see techniques for cooling both the top and bottom side of the device, what we refer to as "double-sided cooling." Integration of the gate driver electronics is also likely. From an application perspective, we'll see SiC in everything from commodity power factor correction (PFC) to renewable energy power converters, charging infrastructure for electric vehicles, onboard automotive power management, and more. And, much like the silicon IGBT has done, the SiC MOSFET looks poised to save a vast amount of energy around the world and reduce emissions in a meaningful way.

Let's talk about some of the pain points circuit designers encounter when they're integrating SiC into their applications.

Designers need to understand is that an SiC MOSFET isn't a direct drop-in replacement for a silicon IGBT, even though some of the early advocates of SiC back in the 1990s pitched it that way. Silicon IGBTs switch much slower than SiC MOSFETs do, so designers didn't have to worry as much about the parasitic inductance and capacitance in the surrounding circuit. But with the high-speed switching that SiC allows, suddenly the existence of parasitic inductance becomes clear in the switching transients—for example, the current falls off so sharply that very large voltage spikes are produced that sometimes can exceed the rating of the power device itself, causing it to fail catastrophically.

SiC exhibits much lower losses than silicon; it also allows for simpler converter topologies in many instances. Circuit designers need SiC device suppliers that employ applications engineers capable and willing to work alongside them to figure out how to take best advantage of SiC in their power converter applications. They must work cooperatively to overcome and optimize the parasitic inductance in the power stage and gate-source loop, assist with layout, help designers select the right passive components, and more. The Dynamic Characterization Platform that Littelfuse and Monolith have developed is one of the tools that supports that cooperative process.

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We welcome the opportunity to publish your opinions. Please email Doug Bess at dlbess@darnell.com.

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