Applications such as power conversion in automotive, consumer and aerospace applications are leveraging the advantages of gallium arsenide (GaN) technology, according to participants in the recent industry event sponsored by Dutch chipmaker Nexperia.

For example, Kubos Semiconductor is developing a new material called cubic GaN. “It’s the cubic form of gallium nitride and we can not only produce it on large-scale wafers — 150 mm and above — but potentially, they can scale to higher wafer sizes and can slot seamlessly into existing production lines,” said Kubos CEO Caroline O’Brien.

Others are working to expand the reach of wide-bandgap (WBG) semiconductors in power management. Ricardo, the U.K. electrification specialist, is expanding its power efforts using both GaN and silicon carbide technologies.

Temoc Rodriguez, Ricardo’s chief engineer, noted that Tesla was the first carmaker to use SiCs instead of insulated-gate bipolar transistors (IGBTs), launching a trend toward greater used of WBG materials to increase power efficiency while reducing size and weight in power converters.

Elsewhere, Hexagem CEO Mikael Björk described the Swedish company’s development of GaN-on-silicon technology designed to reduce cost while increasing scaling advantages in future applications. “We are looking at higher requirements in terms of voltage rating,” said Björk.

Event sponsor Nexperia noted that each new generation of GaN technology continues to make steady gains in performance, gains that could outweigh silicon’s current cost advantages. Those advances come as incremental improvements in silicon technology are marginal, proponents argue.

Applications

Industry sectors ranging from automotive to telecommunications are being pushed to invest in more efficient power conversion and electrification as pressure grows to lower CO2 emissions. Silicon-based power semiconductor technologies such as IGBTs have basic limitations in terms of operating frequency and speed. They also exhibit poor high-temperature and low-current performance. Frequency and high-temperature performance in high-voltage Si FETs are similarly restricted.

Those limitations are prompting more application designers to consider WBG semiconductors. “In applications markets, with improvements in terms of smaller design footprints, and because of the higher efficiencies, I think GaN enables applications that haven’t been recognized or widespread before, such as small base stations,” said O’Brien of Kubos Semiconductor. “There’s a real opportunity there for the smaller system design.”

A key feature is switching frequency response, particularly in applications up to 5–10 kW for DC/DC converters. “That’s kind of a marker that can be considered in telecommunications and energy but also in consumer electronics,” Rodriquez added. “There are plenty of applications centered on DC/DC converters to improve their efficiency and save energy.”

Along with higher voltages, Björk of Hexagem stressed wafer scaling while optimizing production of GaN devices to reduce cost. “Right now, 150-millimeter wafer is the market address, but in the future [production] can scale up to 200-millimeter wafers. And, who knows, there will probably be attempts at 300-millimeter wafers,” Björk predicted.

GaN-on-Si technology, among the most widely used, does not have a good reputation in terms of device development.

“Gallium nitride and silicon have very different lattice constants, so they don’t match,” Björk said. “You have to grow fairly advanced stacks of different layers before you can put GaN on silicon. When you do that, you create a lot of defects, dislocations that are detrimental, losses and premature breakage.

“The other problem is a thermal expansion mismatch between GaN and silicon,” he added. “When you grow this to about 1,000°C, when you cool down these two materials, they shrink at different rates and you can end up breaking the structure.”

Meanwhile, automotive applications ranging from on-board chargers and DC/DC converters to traction and auxiliary inverters are utilizing GaN technologies, said Jim Honea, Nexperia’s GaN applications director. “Development of large batteries for electric vehicles is creating a lot of applications that no one imagined in the past,” Honea said.

Further, low Qrr, or reverse recovery charge, helps simplify filter designs, noted Nexperia’s Dilder Chowdhury, thereby improving switching performance. GaN power transistors also may be used in parallel with common gate-driving circuitry. High voltages and switching frequencies present the greatest challenge, especially for silicon engineers.

As EV makers seek to boost driving range, GaN power ICs are gaining traction as a way to reduce size and weight while increasing efficiency.

GaN can be used to design power electronics systems that are four times smaller and lighter with comparable energy loss when measured against Si-based systems. Zero reverse recovery, which reduces switching loss in battery chargers and traction inverters, as well as higher frequency and faster switching rates are among the benefits.

Furthermore, decreased turn-on and turn-off losses in switches can help reduce the weight and volume of capacitors, inductors and transformers in applications like EV chargers and inverters.

Proponents also assert WBG technology gives power conversion designers new ways to improve efficiency and power density. Like their silicon counterparts, the current-handling capabilities of single GaN devices still have their upper limits. Implementing GaN devices in parallel is a common approach.

GaN size can then be scaled, Honea said. “By putting GaN transistors in parallel, we can scale the power. However, if you put them in parallel, you multiply the resonances, and you have to make sure you don’t excite and amplify them.”

By: DocMemory
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