What You Need to Know About GaN and SiC FETs
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One of the best reasons to be in the electronics industry is because of the rapid pace of development. There are several new technologies that are becoming more widely available, namely silicon carbide (SiC) and gallium nitride (GaN) High Electron Mobility Transistors (also known as ‘FETs’). If you’re an expert in the power electronics field, these transistors are probably familiar. If you’re not and you still want to know what’s new, here’s what you need to know.
Silicon FETs are getting blown out of the water in high power applications. Both SiC and GaN are superior to Si based devices in RF and Power Supply Applications.
First brought to market by Cree in 2011, SiC has a breakdown field strength 10x higher than silicon. This means that less material is needed to withstand high voltages and thus, the ON-resistance can be much lower. This ON-resistance is more stable over wide temperature ranges as well. Compared to silicon, the ON-resistance changes 1/10th as much over a temperature range from 25 °C to 150 °C. Thermal conductivity is also much higher than Silicon or GaN
One of the downsides of SiC technology is that the gate drive requirements are higher. To realize the full benefit and achieve the lowest ON-resistance, the gate driver must have very low impedance and swing from -2 to -5 volts all the way up to +20. Additionally, because of the high breakdown strength, the body diode forward voltage can get up there, sometimes around 4V, so watch out.
SiC really finds its home in high voltage high power applications. The technology can be used to create transistors capable of switching voltages as high as 10kV! For inverters, motor controllers, and other high voltage high power applications, SiC FETs are a good fit. Just remember to design the driver to swing between -2 to +20 volts and mind the body diode current.
GaN FETs have a number of key advantages over MOSFETs on Si, and even SiC. Due to their low gate capacitance, they do very well in high frequency applications. For high efficiency and high density power designs, higher operating frequency can bring down the size of inductors and other supporting passives to lower total system costs. GaN FETs have a much lower gate drive voltage than SiC (4.5V typ) GaN devices have higher electron mobility than Si and SiC devices, and can operate at temperatures up to 450C (even if the rest of your board is on fire). Gan Devices also parallel easily for increased current capability.
GaN does well in high current and high voltage applications, but parts are not comparable to SiC in this area yet. GaN FETs are also more difficult to produce.
GaN FETs are the clear winner in high frequency and high temperature applications. RF amplifiers and very high density power supplies are good applications for these devices.
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