Which is better? SiC or GaN?


It is all well and good to point out that wide-bandgap materials like silicon carbide (SiC) and gallium nitride (GaN) are superior performers to legacy silicon, but what does that really mean to the designer? What application spaces can best benefit from the next generation of semiconductors? There is a difference between frequency-oriented applications like RF and LiDAR and energy-oriented applications like power electronics; wide-bandgap devices, properly chosen, can serve both well.

Speed or robustness?
A good rule of thumb to use is that SiC is rugged, and GaN is fast. Before silicon carbide was produced in high-purity single-crystal ingots for electronics, its primary application was as a grit abrasive (often called Carborundum) and is still sold as the artificial diamond Moissanite. Add that to its high thermal conductivity and very low coefficient of thermal expansion and it is easy to see why SiC is well suited for high-voltage demanding applications like solar and hybrid vehicle inverters.

Gallium nitride, on the other hand, is known for its high switching capability due to its nature as a piezoelectric semiconductor. GaN’s piezoelectricity isn’t motion-related, however, as it is manifested in a quasi-semiconducting stress layer between the doped layers of the device. This novel property gives GaN its high electron mobility as well as its high switching speed. That’s why GaN is often the go-to product today for advanced RF and LiDAR systems in automotive and robotic vision as well as in wireless communications.

These new materials and their advanced properties are opening up opportunities across the industry. As Chris Dries, President and CEO of United Silicon Carbide explains, “Our selling strategy is taking place on a couple of threads, the superjunction market that we can compete with at 650V, the IGBT market, where we can just drop a solution into, and there are also people completely redesigning around SiC MOSFET solutions, that require minus five to plus 20V gate drive, and our cascodes work beautifully in those applications too.”

Changing places
The important thing to remember is that this is only a rough guideline. For example, GaN has been used in some high-power applications challenging both SiC and silicon. A recent exhibit at PCIM showed a GaN-based 7kW electric vehicle battery charger using devices from GaN Systems that delivered a power density of over 4kW/liter (image). There is also the growing world of GaN-on-SiC transistors, leveraging the advantages of each material to create devices that can address extremely demanding applications like advanced radar systems.

There are many ways to exploit the advantages of wide-bandgap semiconductors, and proper device selection (as always) will ensure your design will operate at its optimum.