The Silicon Carbide Race Begins
September 20, 2021
The growing adoption of silicon carbide (SiC) for a variety of automotive chips has reached the tipping point where most chipmakers now consider it a relatively safe bet, setting off a scramble to stake a claim and push this wide-bandgap technology into the mainstream.
SiC holds great promise for a number of automotive applications, particularly for battery electric vehicles. It can extend driving range per charge compared with silicon, reduce the time it takes to charge a battery, and contribute to the overall efficiency equation by providing the same range with lower battery capacity and less weight. The challenge now is to reduce the cost of manufacturing these devices, which is why SiC fabs are migrating from 6-inch (150mm) to 8-inch (200mm) wafers.
“These compelling benefits are leading to mass SiC adoption in BEVs, which brings SiC manufacturing cost reductions due to economies of scale,” said Victor Veliadis, executive director and CTO for the PowerAmerica Manufacturing USA Institute, which was formed by the U.S. Dept. of Energy to accelerate adoption of SiC and GaN power electronics. “It is the major volume application that SiC manufacturers are focusing on, and it is fueling their manufacturing expansions. It is also the reason many newcomers are entering the SiC field, and why we are seeing the intense competition for BEV design wins.”
SiC is being inserted in several EV systems, including the traction inverter, the DC-DC converter, and the on-board charger, according to Veliadis, a professor of electrical engineering at North Carolina State University, which manages PowerAmerica. The technology also can help reduce the time it takes to charge a BEV.
“High-voltage SiC power devices are also key in enabling the fast-charging infrastructure that will lift the last major barrier in wide EV consumer acceptance,” he said. “SiC is highly efficient at the high voltages, enabling fast battery charging times that are comparable to filling the tank of conventional vehicles.”
Following Tesla’s adoption of SiC in its main inverter in 2017, automotive has become the killer application for SiC, noted Ezgi Dogmus, team lead analyst for compound semiconductors and emerging substrates at Yole Développement. “Since then, we have witnessed an interest in SiC from almost all carmakers and Tier 1s. BYD, Toyota, and Hyundai have chosen SiC for their EV models, and Audi, GM, Nio, and Volkswagen are expected to follow,” Dogmus said. “With a significant increase in design wins for SiC solutions, we forecast a bright outlook for the 2020 to 2026 period. In fact, the automotive market is undoubtedly the foremost driver and, as such, will hold more than 60% of the total SiC device market share in 2026.”
Along with EV applications, Dogmus sees a trend to adopt SiC in charging infrastructure, where it offers increased efficiency and reduced system size. In addition, SiC is forecast to grow at a double-digit compound annual growth rate between 2019 and 2026 in applications such as rail, motor drives, and photovoltaics.
SiC vs. GaN
There are significant advantages for SiC in power electronics over standard silicon offerings, as well as other wide-bandgap semiconductors like gallium nitride (GaN).
“The silicon MOSFET has undergone incremental growth and multi-decade improvements and is approaching its theoretical boundaries,” Dogmus said. “Historically, these MOSFET products have been sufficient for their target applications. At the same time, innovative wide-bandgap materials such as SiC and GaN exhibit performance properties that exceed those of silicon-based devices,” Dogmus said. “With a high breakdown voltage, high switching speed, and a small form factor, wide-bandgap materials are promising candidates to complement the power market industry. In addition, they allow a reduction in the number of passive components per system, resulting in a compact design. However, these materials remain expensive compared to silicon.”
Others agree. From a high-level view, positioning of silicon, silicon carbide and gallium nitride is straightforward, according to Robert Hermann, senior director and head of product marketing for high voltage conversion at Infineon Technologies. “Silicon carbide is strongest when it comes to a mix of high-temperature, high power and higher switching frequencies, compared to silicon. This goes with derived system cost reductions for the main inverter and onboard charging.”
Gallium nitride, the other major wide band-gap technology, has even higher efficiency and improved frequency behavior. “These two factors boost power density to a higher level compared to silicon carbide,” Hermann said. “However, to unleash this benefit, larger system changes need to be achieved. Also, complementary semiconductor and passive offerings should be available.”
For now, though, SiC’s real competition in inverters for EV applications and high-power systems is silicon, said Yole’s Dogmus. “For SiC, the cost/performance ratio is attractive at higher voltages. For example, implementing 1,200V SiC devices in 800V battery vehicles will represent a significant market opportunity. Meanwhile, GaN will continue penetrating the fast-charging market for handset applications. In fact, at lower power, GaN represents a better cost-benefit compared to SiC. GaN is also expected to penetrate the datacom and telecom power market for systems with less than 3kW, as well as OBC and DC-DC converters in EV applications.”
Advantages of SiC outweigh barriers
Not all of the test and inspection processes have been fully ironed out yet, and demand for zero defectivity in automotive applications is a high bar for any new material. But many semiconductor makers believe these problems can be overcome relatively quickly and remain extremely bullish on the prospects for SiC chips in electric vehicles.
“While SiC power diodes have been used commercially for many years, SiC MOSFET is the game changer that is rapidly transforming the market landscape of SiC power electronics,” said Ming Su, technical marketing manager, Rohm Semiconductor. “One of the primary drivers of recent market growth is EV power systems. Since SiC MOSFET technology was first adopted in automotive traction inverters a few years ago, the benefit of SiC over silicon devices in energy efficiency and system size reduction has been widely accepted by the automotive industry.”
Su said that today, nearly all automotive OEMs and EV startups already have adopted SiC or are in the product design stages to use SiC in their EV traction inverters and on-board chargers. “SiC devices also have been adopted in fuel-cell vehicles. Additional automotive power converters using SiC include DC-DC converters to step down the battery voltage to 12V or 48V, and wireless battery chargers.”
EVs are undergoing a massive boom right now, fueled by governmental regulations like CO2 emission limits as set by the European Union and other regions. “It is also emphasized by a strong desire by people to protect the environment, while still enjoying a fun driving experience,” said Infineon’s Hermann. “This means increased volumes, stepping out of a big niche and into the future of a mass market for car production — and applying more pricing pressure for OEMs. In this situation, silicon carbide plays a very important role, as it supports various trends in EV power applications.”
This, in turn, opens up a long list of new options for OEMs, and provides an equal number of opportunities for chipmakers.
“One technology benefit of silicon carbide versus IGBTs is higher energy efficiency. This can be illustrated well for the main automotive inverter, where a few percentage points translate directly into larger ranges or and/or smaller batteries,” Hermann said. “As power losses are reduced, the thermal management gets simplified. What this means is, although pure power semiconductor costs are higher compared to IGBTs, SiC reduces system costs significantly. For the EV car buyer the formula is simple — longer range for less cost.”
The efficiency of SiC also can translate into more space inside a vehicle. “Silicon carbide can directly contribute to more space via another application, the automotive onboard charging,” he said. “To increase the range, battery capacities increase. This means power levels for onboard charging need to increase, or it would not be possible to fully charge the battery overnight. Furthermore, there are an increasing number of use cases exist that require bi-directional charging, like vehicle-to-grid. Without design and technology measures, the onboard charger would get larger, taking away existing space within the car. With silicon carbide, not only does efficiency increase, but higher switching frequencies can be realized. This results in smaller passives and reduced cooling effort. In fact, we believe the power density in silicon carbide can be doubled compared to traditional silicon-based solutions, realizing ambitious design targets and reducing the size of onboard chargers.”
Carmakers are moving to an 800V DC bus to increase the amount of power available to the vehicle and the various applications without scaling up the size of electrical connectors, which would add unnecessary weight and size to the EV. SiC is more efficient for these applications than silicon, reducing losses that generate excess heat.
“As a consequence of this voltage, SiC MOSFETs rated at 1,200V are the appropriate design choice instead of using 650V, which would be the more appropriate choice for 400V batteries and systems.” said Filippo DiGiovanni, strategic marketing, innovation and key programs manager for STMicroelectronics’ Power Transistor MACRO Division. “This means that an inverter equipped with SiC is intrinsically more efficient, which results in longer driving distances for given capacity batteries. Also, the less stringent cooling requirements of SiC are another big plus. GaN transistors (or high-electron-mobility transistors, HEMTs) also can be used because of their efficiency benefits for higher-voltage applications, like traction inverters in electric vehicles, but SiC is more efficient than GaN, which has a lateral structure and does not allow high voltage as easily as SiC MOSFETs.”
SiC is a key material for next-generation semiconductors that provides technical benefits in SiC power switching devices, significantly improving system efficiency in electric vehicles EVs, EV charging and energy infrastructure, added Bret Zahn, vice president and general manager for onsemi’s Electric Vehicle Traction Power Module Business Unit. “SiC Power Modules are a popular request, but the SiC bare die segment is also growing quickly.”
Higher voltages, lower overall cost
Moving to higher-voltage architectures for fast charging has broad implications for BEVs.
“At high voltages, the efficiency advantages of SiC become more pronounced compared to those of their silicon counterparts,” said Veliadis. “Today, almost all BEV manufacturers design is at 400V where silicon is very competitive. By going to higher voltages — 800 to 1,000V, for example — faster charging is enabled with reduced weight and better packaging, thanks to much thinner wires, because higher voltage mean fewer current amps at the same power level.”
That helps to shave off costs and make the overall system more efficient. “The EV customer wants to see pricing that is comparable with internal combustion engine offerings. There is more work needed to get there,” he said. “With respect to SiC versus silicon pricing in EVs, the higher cost of today’s SiC devices is offset by the overall system simplification brought by SiC benefits, including higher frequency operation and reduced cooling requirements. In addition, the higher SiC efficiency reduces the number of batteries, which represent a significant cost of EVs. So overall, SiC in EV is competitive and can be cheaper than silicon solutions. The main barriers to mass SiC EV insertion are reliability and ruggedness concerns, as well as the lack of a trained workforce to implement the technologies.”
As fast charging necessitates higher voltage architectures to attain the same power with lower currents (and thus lower weight, volume and cost of wiring) the SiC value proposition will become even more pronounced, he added.
To help push these technologies along, and partly to improve efficiency, OEMs are becoming more vertically integrated. That, in turn, is putting pressure on Tier 1 and Tier 2 vendors to further reduce costs. It also helps to ensure an uninterrupted supply chain, from initial wafer to fabricated devices to meet the high demand.
This is sparking a wave of investment in the SiC arena, including some M&A activity. “Industry acquisitions are a trend,” Veliadis said. “For newcomers to effectively and timely compete with companies that have a long history in SiC technology, acquiring SiC companies that complement their expertise brings synergies and speed to market.”
Case in point: In August, onsemi announced it had entered into a definitive agreement to acquire GT Advanced Technologies, a manufacturer of silicon carbide (SiC) crystalline growth technologies and substrates.
“400V battery voltage is prevalent today, but there is a growing need for 800V battery systems for production starting beyond 2024,” said onsemi’s Zahn. “These systems will likely become the standard as they achieve longer driving range per charge by enabling an increase in density and efficiency without incurring distribution losses or cable-size increase inside the car and on charging stations. SiC’s advantages over silicon technology are even more evident at the 1,200V voltage rating required by the 800V bus. SiC can operate at higher switching frequency and potentially at higher temperatures limited by packaging. Given Tesla’s successful ramp of SiC and the need for higher range, many OEMs are eagerly pushing forward towards implementing SiC electric drivetrains.”
Pressure by governments for reduced emissions, coupled with the growing popularity of BEVs, is propelling silicon carbide, as well as other wide-bandgap materials, to the forefront. All of this takes time, though, and so far SiC and GaN are the leading candidates to replace silicon in some automotive applications.
There is a price to pay for any new materials in terms of yield, defectivity and various manufacturing processes, but SiC has enough benefits for carmakers to start designing it into various components in an electric vehicle. The use of SiC is only expected to grow from here as the auto industry pushes this technology into the mainstream, putting pressure on pricing and closing up any problems that may crop up in the fab.