John Palmour, CTO, Wolfspeed/Cree
It’s no secret that the automotive industry is striving for "zero emissions" transportation, which means manufacturers are rapidly ramping up their electrification programs. Most OEMs target 2025 for significant sales volumes of battery and hybrid electric vehicles (BEV and HEV). To meet customer expectations on range, charge-time and performance, and to approach the critical adoption of emission-free cars, these EVs require power electronic devices capable of efficient and effective operation at elevated temperatures. As a result, power modules are being developed using wide bandgap (WBG) silicon carbide technology.
With global pressure to decrease energy consumption, increase efficiency and reduce greenhouse gases, CO2 emission reduction has become key in every layer of the value chain. Power electronics play an essential role in these demanding challenges. The push for higher efficiency and smaller more compact power management is driving innovation utilizing breakthrough silicon carbide technology. These advanced silicon carbide module technologies will enable higher performance in traction inverters for trains, HVDC for power transmission and distribution, solar and wind inverters, energy storage, and solid-state transformers. For the EV market in particular, this means longer driving distances and faster charging times using the same size battery.
Silicon carbide set to dominate innovative automotive power applications
Automotive OEMs are bringing an increasing number of EV models to the market, but due to their comparably limited range, acceptance by the end user remains subdued. Aerodynamic design, and lighter materials, do help, but are not enough. Automotive power electronics designers need to use advanced SiC technology to meet the high expectations on efficiency and power density.
New silicon carbide components are an improvement over incumbent semiconductor technologies such as silicon (Si) metal-oxide semiconductor field-effect transistors (MOSFETs) and insulated-gate bipolar transistors (IGBTs) by offering much lower losses, higher switching frequencies, higher operating temperature, and robustness in harsh environments. They are particularly useful as the industry moves toward higher capacity batteries that operating at high bus voltages up to 800V with shorter charging times and overall reduced losses.
Silicon carbide semiconductors hold great promise to significantly outperform and replace traditional Si components. These new components have currently reached a level of maturity that has allowed it to rapidly gain ground over Si for demanding applications, such as traction power electronics in EVs and HEVs.
Automotive market driving silicon carbide growth
Where silicon has a breakdown electric field of 0.3MV/cm, silicon carbide can withstand up to 2.8MV/cm, and its internal resistance can be 100 times less than an equivalent silicon MOSFET. As a result, applications can handle the same level of current using a smaller, faster device, resulting in smaller and more efficient systems.
Consequently, silicon carbide inverters allow for smaller cooling solutions and greater thermal-management design flexibility due to significantly less heat generation. Also, silicon carbide inverters deliver a four-fold increase in drive frequency over conventional technology with no efficiency penalty in step-up converter applications, unlocking significant improvements in power output and density by allowing for smaller and lighter peripheral components.
The increased efficiency of silicon carbide-based power semiconductors also increases the range for electric vehicles in contrast to standard silicon technology. Due to high battery costs, the efficient electric drive represents an enormous growth potential for the foreseeable future. In particular, silicon carbide technology in conjunction with the 800V vehicle electrical system voltage makes a significant contribution to further increasing efficiency which can be used to increase range or decrease the amount of expensive batteries needed to deliver the same range.
Advantageous properties of WBG semiconductors
Doubling or tripling the bandgap in comparison to silicon means that silicon carbide devices can tolerate much higher voltages and electric. As a result, the on-resistance of a SiC MOSFET is far lower. This allows the use of a MOSFET, a very high-speed device, in these high voltage applications rather than a slow, lossy silicon IGBT device.
Overall, for a wide range of power applications (not just automotive), the capabilities of silicon carbide make it possible to reduce weight, volume, and life-cycle costs. In turn, dramatic energy savings can occur, and these applications are far more powerful than they were before.
Working toward an improved WBG future
Given the demands of the EV market, companies are making significant strides in the WBG semiconductor space. Notably, Wolfspeed, a Cree Company and a leader in silicon carbide power products, has developed a 1200V 13 mohm of continuous drain current at a case temperature of 25°C. Silicon carbide enables the reduction of EV drive-train inverter losses by 78. This efficiency improvement offers designers new options in terms of range, battery usage, packaging and vehicle design, while ensuring reliability through lower thermal stress.
Click image to enlarge
Figure 2. A Wolfspeed Silicon Carbide Power Module
Wolfspeed´s commitment to silicon carbide devices allows the company to offer industry-leading silicon carbide MOSFETs and silicon carbide diodes for industrial and automotive applications.
The company is currently investing heavily in the expansion of its silicon carbide production by up to 30-times (between 2017 Q1 to 2024) with the creation of the world’s largest silicon carbide fabrication facility in Marcy, NY and a mega materials factory at its U.S. campus headquarters in Durham, N.C.The plan delivers additional capacity for its industry-leading Wolfspeed silicon carbide business with a brand new, state-of-the-art, automotive-qualified 200mm power and RF wafer fabrication facility.
Click image to enlarge
Figure 3. A Wolfspeed Silicon Carbide MOSFET
WBG semiconductors in 2020 & beyond
The growth is primarily based on the fact that the future of silicon carbide in EVs is very promising. It’s clear that with the need for more range and power, as well as faster, more efficient charging, silicon carbide has the physical properties that best meet these needs. As we start a new decade, we are already seeing the demand for its use in EV development skyrocket along with an array of other industries. Those trends don’t show any signs of slowing down and the years ahead promise new waves of innovation as those industries improve their understanding of the technology and its benefits.