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Wolfspeed has signed a strategic supplier agreement with General Motors to develop and deliver silicon carbide (SiC) power devices for GM’s electric vehicles (EV). GM will use Wolfspeed’s products specifically in its Ultium Drive propulsion units in its next-generation EVs.
In an interview with EE Times, Guy Moxey, senior director of power poducts, Wolfspeed, highlighted how SiC is scaling the EV market in two different ways: product technology and capacity.
“With our technology, we are continuously driving for lower RDS(on), larger die sizes, and higher ampacity packaging. We anticipated a growing demand for silicon carbide and started seriously investing in capacity expansion about three years ago with the expansion of our materials facility in North Carolina and our new Mohawk Valley fab, located in Upstate New York, which is coming on line in the first half of 2022. This will be the world’s largest, 200mm and automotive-qualified silicon carbide fabrication facility. We also believe that demand for silicon carbide will only increase in the coming decades, so our capacity expansion will need to continue after the completion of the Mohawk Valley fab,” said Moxey.
Silicon carbide technology
Silicon carbide is the next step in energy management for e-mobility applications. This valuable material can improve the efficiency of electric vehicles by making batteries more compact and improving range with less energy consumption.
The inherent advantages of silicon carbide-based power switches, in terms of power density and efficiency, offer significant benefits for system cooling and size. Silicon Carbide power switches, as compared to traditional silicon, can provide a longer range and/or a smaller battery pack, resulting in a positive cost comparison from the device to the system level. The traction inverter remains the focal point for improvements targeted at increasing EV efficiency and range. Silicon carbide power switches, being the most expensive and functionally crucial component of the traction inverter, must be precisely regulated to reap the full benefit of the higher switch cost.
As part of the agreement, GM will participate in the Wolfspeed Assurance of Supply Program (WS AoSP), which aims to ensure domestic, sustainable and scalable materials for EV production. According to GM, the goal will be electrification and the next customers will be looking for greater autonomy.
Automotive drivetrains are both 400V and 800V systems. Moxey said, “Higher kW drivetrains usually incorporate silicon carbide modules or custom application packages; however, we also see discrete product being designed into lower kW machines. Silicon carbide is not just used in passenger EVs, but also E-buses, E-trucks, E-motorbikes, industrial mobility machines, e-boats and even E-jet skis! Customers gravitate towards Silicon Carbdie for its abililty to imporve range in EV applications, but also for it’s power density and lower system losses,” said Moxey.
The SiC power device solutions will be produced at Wolfspeed’s 200mm capable Mohawk Valley Fab in Marcy, New York, to expand the capacity of silicon carbide technologies in other industries. In silicon processing, moving to larger wafer sizes was one of the ways to increase production without adding new fabs. That option has been harder for companies working with wide bandgap semiconductors such as SiC (and gallium nitride).
SiC is an incredibly difficult material to grow. It is grown very slowly at high temperatures — above 2,000°C — in a process that is very difficult to control, and fabrication techniques are improving rapidly, thus offering significant cost reductions.
“Increasing wafer size is not an easy thing to do. It has been a long process with years of R&D to be able to manufacture 200mm wafers in the worlds largest silicon carbide fab. There is a massive difference between tinkering with a handful of 200mm substrate prototypes, to having the volume and quality needed to satisfy the likes of Borg Warner, HAPG, ZF and GM. This is not a casual or quick business decision. For others in the industry thinking or talking about fab construction or converting facilities from silicon to silicon carbide, they should expect an interesting, lengthy and costly experience. This is why Wolfspeed’s vertical integration technology has been absolutely critical as the 200mm supply chain “cycles of learning” have all been in-house. Technology development and perfection (from raw materials to the finished product) are entirely linked,” said Moxey.
The big cost difference between silicon carbide and silicon today is in the substrate itself. Future cost reductions will be an important factor in how quickly Silicon Carbide will be adopted in EVs. The economic benefits of Silicon Carbide are greatest in long-range cars, those with the largest batteries.