WBG Devices Riding on EV Growth

Article By : Anne-Françoise Pelé

In a panel session on wide-bandgap semiconductors for EVs at the recent Advanced Automotive Tech Forum, three industry experts discussed efforts to address GaN and SiC current challenges and future opportunities.

Wide-bandgap power semiconductors such as silicon carbide and gallium nitride reduce component size, increase efficiency, and improve performance in hybrid and all-electric vehicles. More and more car manufacturers now bet on SiC and GaN, and chipmakers are transforming their business to take advantage of the electric-vehicle market’s explosive growth.

In a panel session on wide-bandgap semiconductors for EVs at the recent Advanced Automotive Tech Forum, three industry experts discussed efforts to address GaN and SiC current challenges and future opportunities.

Harnessing momentum for electrification

In the clean-energy sector, the EV market is by far the most dynamic. In 2012, about 130,000 electric cars were sold worldwide. Today, that is the number of electric cars sold in a single week.

The Covid-19 pandemic severely impacted the conventional car market, but it did not dampen EV sales. Recent figures from the International Energy Agency (IEA) reveal that 2.2 million electric cars were sold in 2019 and 3 million in 2020, while EV sales more than doubled to 6.6 million in 2021, representing close to 9% of the global car market. The net growth in global car sales in 2021 came from electric cars.

Driven by government subsidies and other incentives, China led the global growth of electric-car markets in 2021, nearly tripling sales to 3.4 million, according to the IEA. The Chinese government’s official goal is for electric cars to reach a 20% market share by 2025.

As part of the Green Deal, the European Union has set itself the ambitious target of achieving neutrality by 2050 and has decided to ban the sale of new fossil-fuel cars after 2035. As a matter of fact, electric-car sales rose by nearly 70% to 2.3 million last year. And this is only the beginning.

It’s not just car manufacturers that have to adapt and keep pace with EV penetration rates. Power chip suppliers are scrambling to meet demand for EV powertrain components such as on-board chargers, traction inverters, and DC/DC converters.

“The market is undergoing a revolution, and the role of the Tier 1 is completely redefined,” said Pietro Scalia, director of automotive traction solutions at onsemi. “The semiconductor players have a great opportunity to step up and grab areas of competencies, because it is all about systems.”

According to U.K.-based research firm IDTechEx, the demand for semiconductors per EV is about 2.3× that of internal combustion-engine vehicles. By 2022, with current trajectories and assuming no supply constraints, IDTechEx predicts that electrification in the automotive sector (BEV, PHEV, FCEV, HEV, 48 V) will demand an additional $7.4 billion worth of semiconductor material compared with a scenario without electrification.

A question then arises: Is electrification sustainable in the face of semiconductor shortages?

“If you want to electrify your fleet, you cannot do it in one year; you need five or 10 years,” said Scalia. “OEMs are coming to seal long-term agreements — not just commercial agreements but also technological agreements. Customers want to know our roadmap to where the figure of merit of specific resistance will be in three years from now, because today they buy the die at some performance but they will definitely need to update their power module.”

Besides continued interactions with OEMs, Scalia emphasized that a robust supply chain is “essential” and multi-continent sourcing is “super important.”

Phoenix-based onsemi claims that its SiC MOSFETs and SiC diodes are currently used in EVs and that it has cooperation projects with automotive OEMs in every region of the world.

“There is no question that wafer shortage in silicon carbide has hampered the growth of the [EV] market,” said Filippo Di Giovanni, strategic marketing manager of the Power Transistor Macro Division at STMicroelectronics (ST). To address global capacity constraints and bring substrate design and production in-house, ST acquired Swedish SiC wafer maker Norstel for $137.5 million in late 2019. It, however, takes time to build high-volume capacity for substrates, and Di Giovanni said ST has signed “big and strategic supply contracts with partners, worth hundreds of millions of dollars, in order to have continuity and access to substrates.” The objective is to have “at least 40% of our substrate demand produced internally” by 2025.

In these uncertain times, building resilience in manufacturing and supply chains is a priority. Because demand is mainly concentrated in two world regions, ST’s Di Giovanni said, “We have grown the capacity quite fast [with] the second production plant in Singapore, which is very close to China … and introduced a second assembly line very close to Europe, in Morocco, Casablanca.”

Nexperia also favors a dual sourcing approach to mitigate supply chain risks. “Within the automotive industry, you need dual sourcing, and that’s why we have got the European source and the Far Eastern source,” said Dilder Chowdhury, director strategic marketing for Power GaN technology at Nexperia.

Transitioning to 8-inch wafers

Next-generation EVs will require technology that meets the stringent requirements of high efficiency and reliability, defect elimination, and cost reduction. SiC and GaN power semiconductors offer automakers promising solutions, and a transition from 150-mm (6-inch) to 200-mm (8-inch) wafer production is underway.

While increasing the wafer size significantly reduces the unit cost of components, it poses major challenges in eliminating defects and increasing the reliability of the delivered semiconductor.

In July, ST announced it had manufactured the first 8-inch SiC bulk wafers for prototyping next-generation power devices from its facility in Norrköping, Sweden. These initial wafers were of “high quality, with minimal yield-impacting and crystal-dislocation defects,” the company claimed.

ST currently manufactures its STPOWER SiC MOSFETs on two 6-inch wafer lines in its fabs in Catania (Italy) and Ang Mo Kio (Singapore) and performs assembly and test at its back-end sites in Shenzhen (China) and Bouskoura (Morocco). “Existing equipment that processes 6-inch wafers can also process 8-inch wafers,” said Di Giovanni. “The switch over to 8 inch will be quite smooth and will not imply purchasing brand-new equipment.”

Similarly, Scalia said onsemi currently produces 6-inch wafers because “that’s the market standard.” Yet the company acquired GT Advanced Technologies (GTAT) in November 2021 with the intention to invest in expanding GTAT’s manufacturing facilities, supporting research and development efforts to advance 150-mm and 200-mm SiC crystal growth technology. “GTAT is engaged in 8 inch, and we are testing material already,” he said. “It’s not an easy walk, but it’s a necessary walk. We all need 8 inch.”

A shift to 8 inch is also occurring for GaN wafer production.

“GaN [wafers] are currently coming in 6 inch, but we plan to translate [them] to 8 inch, and we believe the volume ramp-up and our 8-inch transition will be compatible with the timeline we see in the market,” said Chowdhury.

On another level, Infineon and Panasonic recently announced they were developing a second generation of 8-inch GaN-on-Si wafers for launch in 2023.

Likewise, Suzhou, China-based Innoscience has two fabs dedicated to 8-inch GaN-on-Si device manufacturing and produces normally off (e-mode) GaN devices for a wide range of applications and voltages — low voltages (down to 30 V) and high voltages (up to 650 V). Innoscience said production is now at 10,000 wafers per month but will reach 14,000 wafers per month by the end of this year and 70,000 wafers per month by 2025.

Extending battery range

The traction inverter converts energy from the vehicle’s battery to drive the powertrain motors. It directly impacts the vehicle’s driving performance, range, and reliability, particularly due to its weight and size.

“The main reason why SiC is so important in car electrification is its role in the traction inverter,” said Di Giovanni. “Thanks to the drastic improvement in efficiency, a given car can be driven for a much longer range.”

Di Giovanni added, “Designers have the possibility to reduce constraints on cooling systems. The cooling system is one of the most expensive blocks inside the vehicle, and the fact that a given driver can drive a car for longer distances will help to soothe the so-called range anxiety that has basically haunted potential buyers of electric vehicles.”

Nexperia has been partnering with automotive engineering company Ricardo on an EV traction inverter based on GaN technology. “We see the benefit of extending the range for the same battery power or we can reduce the battery sizes for the same range,” said Chowdhury.

Addressing thermal management

To harness the potential of wide-bandgap semiconductors, designers must estimate the challenges inherent in using these materials. By operating at higher switching frequencies and power density, it is possible to reduce the size of passive components (inductors and capacitors) and build lighter, smaller systems. However, thermal management issues could arise.

“Needless to say, material innovation should go hand in hand with packaging innovation, not to waste or offset the big improvements brought by the new materials,” said Di Giovanni. ST’s ACEPack, for instance, “allows customers to mount this package into the heatsink using silver sintering techniques. Not only is the die attached to the package with silver sintering, but the back finishing is made in such a way that it can also be mounted onto heatsinks using the same technique, and we know that silver sintering is far superior to soldering techniques in terms of thermal resistance and long-term reliability.”

ST and French carmaker Renault have also sealed a partnership on the design, development, manufacturing, and supply of ST’s products and related packaging solutions for the power-electronic systems of battery-operated and hybrid vehicles. “We are developing the next generation of SiC and GaN power modules and devices to meet their ambitious plans to introduce EVs in the future,” Di Giovanni said. Based on its experience in using its copper-clip technology, Nexperia has developed the CCPAK surface-mount packaging to replace internal bond wires and eventually “get better thermal,” said Chowdhury. Due to the high thermal performance of GaN, “it is key to get the high-density power to dissipate and along with cooling systems like PIN FIN technology.”

This article was originally published on Power Electronics News.

Anne-Françoise Pelé is editor-in-chief of eetimes.eu and EE Times Europe.


Subscribe to Newsletter

Leave a comment