GaN and SiC Technology

Efficiency Gains in Traction Applications Using SiC Devices

Efficiency targets get progressively tougher, and understandably so — every fraction of a percent gain forms part of a virtuous circle of smaller size, weight, and cost, as well as longer driving range. Figures achieved of about 98% with IGBTs are creditable, but there is pressure to improve further. The residual switching losses can be reduced by using silicon or silicon carbide MOSFETs, but historically, they have had higher conduction losses than IGBTs at high power levels. This stems from their on-resistance, dissipating power that scales with the square of the current. IGBTs have a relatively fixed saturation voltage, so there is a crossover point at high power where IGBTs still win. To put it in perspective, at 500 A, a MOSFET would need an on-resistance of about 3 mΩ at the operating junction temperature for conduction loss comparable to an IGBT. In EV traction applications, devices need ratings of 650 to 750 V, and that on-resistance is not yet achieved at those voltages with single Si or SiC MOSFET devices. Paralleled MOSFETs are a solution, but then costs and complexity spiral.?

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Moving GaN Technology to the Next Stage

Gallium nitride (GaN) is a?wide-bandgap ?semiconductor material, which, compared with silicon, exhibits outstanding characteristics and performance, including high efficiency, high switching rate, excellent thermal management, and small footprint and weight. To achieve a large adoption of?GaN-based devices ?in power applications, some barriers still need to be overcome, mainly related to its large-volume manufacturing and price reduction.?

GaN technology has evolved considerably over the years. Until around 2010, companies were busy in the R&D phase proving this innovative technology. The second phase, from 2010 to 2015, saw the first devices coming out in the market. This represented a big change that allowed people to buy GaN devices and start using them in real projects. Phase 3 began around 2015, when system engineers realized that GaN was not plug-and-play. They could not just replace silicon with GaN to get a better system; rather, they had to redesign their product to take advantage of GaN’s increased performance.?

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