Wide bandgap materials possess bandgaps—the energy needed to excite electrons from the material’s valence band into the conduction band—significantly greater than that of silicon; silicon (Si) has a bandgap of 1.1 eV (electronVolt); silicon carbide (SiC) has a bandgap of 3.3 eV, while gallium nitride (GaN) has a bandgap of 3.4 eV. The wider bandgaps allow the WBG materials to withstand far higher voltages and temperatures than silicon.

Accordingly, compared to silicon-based technologies, wide bandgap semiconductors can operate at higher temperatures and have greater durability and reliability at higher voltages and frequencies—ultimately achieving higher performance while using less electricity.

In electronic devices, WBG semiconductors can eliminate up to 90% of the power losses that currently occur during AC-to-DC and DC-to-AC electricity conversion, and they can handle voltages more than 10 times higher than Si-based devices, greatly enhancing performance in high-power applications. Applied in an EV, WBG materials could cut electricity losses by 66% during vehicle battery recharging, the DOE says. They also offer greater efficiency in converting AC to DC power and in operating the electric traction drive during vehicle use.

Efficient power electronics is key to a smaller battery size, which in turn has a positive cascading impact on wiring, thermal management, packaging, and weight of electric vehicles. In addition to power electronic modules, opportunities from a growing number of consumer applications—such as infotainment and screens—will double the number of power electronic components built into a vehicle.

—Pallavi Madakasira, Lux Research Analyst and report author

Lux Research analysts evaluated system-level benefits WBG materials are bringing to the automotive industry, and predicted a timeline for commercial roll-outs of WBG-based power electronics. Among their findings:

• Power saving threshold lower for EVs. At 2% power savings, if battery costs fall below $250/kWh, SiC diodes will be the only economic solution in EVs requiring a large battery, such as the Tesla Model S. However, for plug-in electric vehicles (PHEVs), the threshold power savings needs to be a higher 5%.

• SiC ahead in road to commercialization. SiC diodes lead GaN in technology readiness and will attain commercialization sooner, based on the current Technology Readiness Level (TRL). Based on the TRL road map, SiC diodes will be adopted in vehicles by 2020.

• Government funding is driving WBG adoption. The US, Japan and the United Kingdom, among others, are funding research and development in power electronics. The US Department of Energy’s Advanced Power Electronics and Electric Motors (APEEM) is spending $69 million this year and defining performance and cost targets; the Japanese government funds a joint industry and university R&D program that includes Toyota, Honda and Nissan.

As just one example of government funding, the US DOE is contributing $1.8 million to a $3.8-million project led by APEI, in collaboration with Toyota Motor Engineering & Manufacturing North America, Inc.; GaN Systems, Inc.; the National Renewable Energy Laboratory; and the University of Arkansas National Center for Reliable Electric Power Transmission, to develop two independent 55 kW traction drive designs (one SiC-based and one GaN-based) to showcase the performance capabilities of WBG power devices.

These capabilities include high efficiency and increased gravimetric and volumetric density obtained from a high operating junction temperature capability.

The goal of that project—which is providing a unique, direct comparison between inverter designs using SiC and GaN—is to reduce traction inverter size (≥ 13.4 kW/L), weight (≥ 14.1 kW/kg), and cost (≤ $182 / 100,000) while maintaining 15-year reliability metrics.

The Next Generation Power Electronics Institute announced by president Obama earlier this year (earlier post) is focused on making WBG semiconductor technologies cost-competitive with current silicon-based power electronics in the next five years.

Resources

• Burak Ozpineci, Leon Tolbert (2011) “Silicon Carbide: Smaller, Faster, Tougher” IEEE Spectrum