The wide-bandgap revolution is still in its infancy, but we have finally reached the point where promise is being followed by product. Every major embedded manufacturer now has a wide-bandgap play, if only to demonstrate to the marketplace that they are players. Partnerships between the technology developers and mainstream semiconductor companies are coupling disruptive tech with trusted sources to ease migration pains. Both silicon carbide (SiC) and gallium nitride (GaN) have now established themselves in the marketplace and are poised to take the embedded power electronics industry
But what is the difference between the two wide-bandgap semiconductors currently in the marketplace? What application spaces are each best suited for? Is there a “sweet spot” for each? What does it mean for silicon devices? While each wide-bandgap material has advantages over silicon, and some overlap, each flavor has its own story.
The easiest way to sum up silicon carbide’s primary attribute is to point out that the cones left over from SiC ingot manufacture are sold to the jewelry industry, where they are used as Moissanite artificial diamond. In fact, until the recent advances in SiC crystal growth, the primary application for SiC was sandpaper. Because SiC sublimates, and has no liquid phase, all SiC ingots must be grown in a high-energy plasma, which is why state of the art ingot manufacturing is still at six inches, half that of current silicon ingot growth. There are also companies making N-type and P-type SiC epitaxial layers on SiC substrates.
SiC’s hardness is related to its high thermal- and voltage-handling attributes. SiC MOSFETs can replace silicon devices by providing a higher blocking voltage of over 1700V, with avalanche rating of over 1800V. This high blocking voltage comes with a low on-resistance, crucial to energy efficiency and improved thermal performance. So not only can SiC handle higher temperatures, it has a low thermal expansion and a high thermal conductivity, both very useful to the power system designer.
Gallium nitride is a very interesting material with very interesting properties. While it’s not a brute-force improvement in performance in the manner of SiC, GaN leverages piezoelectric stress between its doped layers to create a pseudo-superconducting field where the magic happens. This allows a GaN product to deliver switching losses up to three times lower than traditional devices, at frequencies of over five times that of silicon. This can enable the creation of a power system with a power density several times that of legacy supplies.
GaN also has a low sensitivity to ionizing radiation, making it well suited for space-based solar applications. GaN transistors can also operate at much higher temperatures and work at much higher voltages than gallium arsenide (GaAs) transistors, good for power amplifiers at microwave frequencies. GaN is so good at high-frequency operation that it also is showing an application dominance in RF and LIDAR systems as well.
Choose to use
As Peter Friedricks of Infineon pointed out, “we offer all three embedded technologies, Silicon, SiC, and GaN. We are frequently asked about the differences and applications. The split we have developed is using GaN as a solution for very fast switching, very high-end switchmode power supplies, 600V, very high efficiency. We use SiC complements systems in the area of 1000V and above, to as high as 3.3kV, and also in high-performance applications driven by high power densities. For the others, we still use silicon.”
Each material has its pluses and minuses, and proper design-in will result in the best solution for the given application. The addition of wide-bandgap to the mix has provided a significantly expanded palette of solutions to the power systems designer.