Choice between Si, SiC and GaN Growing in Complexity

December 21, 2016 by Jeff Shepard

A team of authors from Infineon and the Power Electronic Systems Laboratory, ETH Zurich, presented a detailed analysis of the technical tradeoffs facing power conversion engineers when choosing between Si, SiC and GaN power devices for various power converter designs. The paper, "Si, SiC and GaN power devices: an unbiased view on key performance indicators" was presented at the recent IEEE International Electron Devices Meeting.

The paper discusses key parameters such as capacitances and switching losses for Si, SiC and GaN power devices with respect to applications in switch mode power supplies. Whereas wide bandgap devices deliver roughly one order of magnitude lower charges stored in the output capacitance, the energy equivalent is nearly on par with latest generation super junction devices. Silicon devices will hence prevail in classic hard switching applications at moderate switching frequencies whereas SiC and GaN based power devices will play to their full benefits in resonant topologies at moderate to high switching frequencies.

The authors note: “The recent introduction of SiC power devices with voltage ratings below 1200V and the availability of 600V GaN HEMTs offer the designer of power supplies operating from single-phase ac line a number of choices. As the power supply industry pushes along towards new frontiers in terms of efficiency and density, the matching of topology, control and device selection becomes a crucial task.”

Conceptsuper junctionplanar MOSFETeMode HEMT
Blocking voltage600V900V600V
On-state resistance (typ.)56 mOhm65 mOhm55 mOhm
Reverse recovery charge6000 nC130 nC0 nC
Energy stored in Coss @ 400V8.1 µJ8.8 µJ6.4 µJ
Charge stored in Coss @ 400V420 nC70 nC40 nC
Turn-off loss @ 10A / 400V15 µJ10 µJ10 µJ

They analyze both device selection parameters and topology selection considerations related to the identification of the “optimal” combination of device and topology for specific use cases. Key performance indicators for Si, SiC and GaN based power devices are also discussed in the context of suitable topologies and control methods.

The paper concludes: “GaN HEMTs will offer significant benefit versus silicon based power devices in topologies with continuous commutation of current in bridge based topologies, such as totem pole and in resonant topologies at moderate to high switching frequencies. The value proposition of SiC devices relies on the same arguments than for GaN devices with key performance indicators however not entirely reaching the level of corresponding GaN power devices. Silicon power devices will prevail in many applications including both hard and resonant switching at moderate frequencies.”

The authors of this paper included; G. Deboy, M. Treu, and O. Haeberlen with Infineon Technologies Austria AG, Power management & Multi market Division and D. Neumayr with the Power Electronic Systems Laboratory, ETH Zurich, Switzerland.