SiC: ideal material for extreme power devices
SiC is a compound semiconductor material composed of silicon and carbon, which is very stable in thermal, chemical, and mechanical aspects. The different combinations of C and Si atoms give SiC a variety of lattice structures, such as 4H, 6H, 3C and so on. 4H-SiC can provide a higher current density because of its higher carrier mobility, and is often used as a power device.
SiC began to be developed in the 1970s. In 2001, SiC SBD was commercialized, SiC MOSFET was commercialized in 2010, and SiC IGBT was still under development. With the reduction of defects and quality improvement of 6-inch SiC single crystal substrates and epitaxial wafers, the preparation of SiC devices can be carried out on the current growth lines of current 6-inch Si-based power devices, which will further reduce the cost of SiC materials and devices, and promote The popularity of SiC devices and modules.
The advantages of SiC devices over Si devices mainly come from three aspects: reducing energy loss in the process of power conversion, easier to achieve miniaturization, and more resistant to high temperature and high pressure.
• Reduce energy consumption. The switching loss of SiC material is extremely low. The switching loss of a full SiC power module is much lower than that of the same IGBT module. The higher the switching frequency, the greater the loss difference with the IGBT module, which means that it is not good at IGBT modules. High-speed switching operation, the full SiC power module can not only greatly reduce the loss but also achieve high-speed switching.
• Low resistance makes it easier to achieve miniaturization. The SiC material has a lower on-state resistance, and the chip area can be reduced under the same resistance value. The size of the SiC power module can reach only about 1/10 of that of Si.
•More resistant to high temperature. The forbidden band width of SiC is 3.23ev, and the corresponding intrinsic temperature can be as high as 800 degrees Celsius, which can withstand a higher temperature than Si; SiC material has a thermal conductivity of 3.7W/cm/K, while that of silicon material is only 1.5 W/cm/K, higher thermal conductivity can bring about a significant increase in power density, while the design of the heat dissipation system is simpler, or natural cooling can be used directly.
The SiC production process is divided into three major steps: SiC single crystal growth, epitaxial layer growth, and device manufacturing, which correspond to the three major links of the industry chain substrate, epitaxy, devices and modules.
SiC substrate: SiC crystals are usually manufactured by the Lely method. International mainstream products are transitioning from 4 inches to 6 inches, and 8-inch conductive substrate products have been developed, while domestic substrates are mainly 4 inches. Since the existing 6-inch silicon wafer production line can be upgraded for the production of SiC devices, the high market share of 6-inch SiC substrates will remain for a long time.
SiC epitaxy: usually manufactured by chemical vapor deposition (CVD) method. According to different doping types, it is divided into n-type and p-type epitaxial wafers. Domestic Hantian Tiancheng and Dongguan Tianyu have been able to provide 4 inch/6 inch SiC epitaxial wafers.
SiC devices: 600~1700V SiC SBD and MOSFET have been industrialized internationally. The withstand voltage level of mainstream products is below 1200V, and the packaging form is mainly TO package. In terms of price, the price of SiC products in the world is 5-6 times that of corresponding Si products, and is declining at a rate of 10% per year. With the expansion of upstream materials and devices, the market supply will increase in the next 2 to 3 years. It will further decline. It is expected that when the price reaches 2~3 times of the corresponding Si product, the advantages brought by the reduction of system cost and the improvement of performance will promote SiC to gradually occupy the market space of Si devices.
The global SiC industry structure presents a three-pronged situation of the United States, Europe, and Japan. Among them, the United States is the largest in the world. 70% to 80% of global SiC production comes from American companies. Typical companies are Cree and Ⅱ-VI; Europe has a complete SiC substrate, epitaxy, device and application industrial chain, and the typical company is Infineon , STMicroelectronics, etc.; Japan is a leader in equipment and module development. Typical companies are Rohm Semiconductor, Mitsubishi Electric, Fuji Electric, etc.
SiC market: cars are the biggest driving force
SiC devices are being widely used in the field of power electronics. Typical markets include rail transit, power factor correction power (PFC), wind power (wind), photovoltaic (PV), new energy vehicles (EV/HEV), charging piles, and Discontinuous power supply (UPS), etc. According to Yole’s forecast, the SiC power device market will grow at a compound growth rate of 31% per year from 2017 to 2023, and will exceed $1.5 billion in 2023. Cree, the leader in the SiC industry, is more optimistic. SiC's market space for electric vehicles will rapidly grow to USD 2.4 billion, which is 342 times the overall revenue of automotive SiC (USD 7 million) in 2017.
In 2022, the scale of SiC in the electric vehicle market will reach 2.4 billion US dollars
SiC is one of the ideal materials for making high-temperature, high-frequency, high-power, and high-voltage devices. The technology has also matured, making it an ideal choice for achieving the best performance of new energy vehicles. Compared with traditional solutions, SiC-based solutions make the system more efficient, lighter and more compact. At present, the applications of SiC devices in EV/HEV are mainly power control units, inverters, DC-DC converters, and car chargers.
SiC devices improve the system efficiency of electric vehicles in four key areas
Power control unit (PCU) for new energy vehicles. The PCU is the central nerve of the car's electric drive system, which manages the flow and transmission speed between the electric energy in the battery and the motor. Traditional PCU is made of silicon-based material semiconductors. The power loss when high current and high voltage pass through silicon transistors and diodes is the main source of power loss for hybrid vehicles. The use of SiC greatly reduces the energy loss in this process. By replacing the traditional PCU with Si diodes with SiC diodes and Si IGBTs with SiC MOSFETs, the total energy loss can be reduced by 10% and the device size can also be greatly reduced. , Making the vehicle more compact. Toyota Central Research and Development Laboratory (CRDL) and Denso Corporation have been cooperating to develop SiC semiconductor materials since the 1980s. In 2014, the two parties formally released a new energy vehicle PCU based on SiC semiconductor devices, which is a typical representative of this field.
Inverter for vehicle. SiC is used in vehicle inverters, which can greatly reduce the size and weight of the inverter, and achieve light weight and energy saving. Under the same power level, the package size of the full SiC module is significantly smaller than that of the Si module, and it can also reduce the switching loss by 75% (the chip temperature is 150°C);
In the same package, the full SiC module has a higher current output capability and supports the inverter to achieve higher power. Tesla Model 3 uses a SiC inverter produced by STMicroelectronics (later added Infineon), and is the first car company to integrate a full SiC power module in the main inverter. On December 2, 2017, ROHM provided the VENTURI team with an inverter made of full SiC power modules in the fourth season of the “FIAFormula E” Championship, the world’s top electric car event, which made the inverter size comparable to the second season. A 43% drop and a 6kg lighter weight.
Car charger. SiC power devices are accelerating their application trend in the field of on-board chargers. At PCIM Europe 2018, a number of manufacturers launched SiC power device products for HEV/EV and other electric vehicle chargers. According to Yole statistics, as of 2018, more than 20 car manufacturers have adopted SiC SBD or SiC MOSFET devices in their car chargers, and this market will maintain a 44% growth by 2023.