TECHNOLOGY SiC POWER ELECTRONICS
Ultra-high voltage devices for future power infrastructure Fast growth of high-quality SiC epilayers has paved the way to the
fabrication of power devices with blocking voltages exceeding 20 kV. By TSUNENOBU KIMOTO FROM KYOTO UNIVERSITY, JAPAN
Figure 1. Different voltage ratings are required for different applications
FOLLOWING RESEARCH stretching back more than 40 years, shipments of SiC power devices are now significant and rising fast. Two of the biggest sellers are Schottky barrier diodes (SBDs) and power MOSFETs, which are increasingly displacing silicon incumbents and enabling the construction of smaller, more efficient power converters and inverters. Thanks to this, SiC chips will be winning deployment in power supplies, motor controls, photovoltaic converters, telecommunications equipment, heating, robotics, electric/hybrid vehicles, traction and electric power transmission (see Figure 1). According to several institutes, one impact of this trend is that by 2025, SiC power devices will produce a combined electric power saving exceeding 10 GW – that’s comparable to the power generated by about ten nuclear plants.
Today, a time when the revolution in power electronics is still in its infancy, the operating voltages of commercial SiC diodes and transistors are predominantly in the 600 V - 1.7 kV range. But that’s by no means the limit of what is possible – recent progress in the labs shows that blocking voltages of more than 20 kV are attainable. This opens up the possibility for innovative hardware for electric power infrastructure, advanced traction applications and accelerators of particles, such as electrons and protons.
Devices that combine ultra-high blocking voltages with very low losses can also play a key role in the future of electric power transmission/ distribution infrastructure and smart grids. They could feature in distributed power lines, which operate in the 6.6–7.2 kV range, and could be the 13–15 kV power devices required for the construction of single-level converters. Another attractive opportunity for the deployment of ultra-high-voltage SiC devices is in solid-state transformers (see Figure 2). In high-voltage DC power transmission, voltages can be as high as 150–250 kV. Today, a number of 6–8 kV silicon thyristors are stacked in series to provide conversion of electrical power at such high voltages, but this has the downsides of enormous energy dissipation and self-heating. If ultra-high- voltage SiC chips could replace these devices, this would lead to considerable energy savings.
To help turn this dream into a reality, our team of researchers at Kyoto University has been developing SiC devices that are now setting a new benchmark for high-voltage operation. These chips, which are formed using the high epitaxial growth rates needed for a viable production process, can withstand voltages of almost 27 kV.
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www.compoundsemiconductor.net March 2014
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