Silicon nitride ceramics in the field of new energy vehicles
Silicon nitride possesses excellent properties such as high flexural strength, high fracture toughness,good creep resistance, high hardness, and high wear resistance. It is considered the best-
performing material among the structural ceramic family. As a rapidly growing strategic emerging industry with continuous technological innovation, the demand for ceramic components in the field of new energy vehicles is increasing, and silicon nitride plays multiple important roles.
Firstly, silicon nitride bearings are critical components known as the "chips" of the mechanical industry. They are mainly used to support rotating machinery and reduce friction coefficients, ensuring precise rotational performance. Silicon nitride has a density of approximately 42% of bearing steel, a high elastic modulus of 320 GPa, a tensile strength of 1600 MPa, and a compressive strength of up to 3600 MPa. Furthermore, its mechanical properties remain nearly unchanged below 900°C, making it an ideal material for rolling bearing rolling elements. Currently, bearings that use silicon nitride balls as rolling elements have become the most popular, high-performance, and widely used advanced ceramic bearings worldwide. In the field of new energy vehicles, the adoption of silicon nitride bearings is mainly driven by the following reasons:
1. Electric motor bearings require materials with low density and higher wear resistance to adapt to
higher speeds.
2. The alternating current generated by the motor causes changes in the surrounding electromagnetic field, requiring good insulation performance to reduce bearing discharge-induced corrosion.
3. The bearing balls need to have a smooth surface and minimal wear. Ceramic balls, due to their low density, high hardness, and excellent wear resistance, are highly suitable for high-speed rotating conditions. They are particularly irreplaceable in high-temperature, strong magnetic, and high-vacuum environments. In the field of new energy vehicles, ceramic bearings have gradually replaced steel ball bearings.
Secondly, silicon nitride ceramic substrates are ceramic plates made by sintering silicon nitride powder 
with a small amount of oxide and rare earth materials. These substrates exhibit excellent comprehensive performance and reliability, including high thermal conductivity, high mechanical strength, low coefficient of thermal expansion, oxidation resistance, thermal corrosion resistance, low dielectric loss, and low friction coefficient. Silicon nitride ceramics have an extremely high theoretical thermal conductivity (approximately 400 W/(m·K)) and a low thermal expansion coefficient (approximately 3.0x10-6℃), making them compatible with materials such as Si, SiC, and GaAs. Therefore, the high strength and high thermal conductivity of silicon nitride substrates meet the requirements of high temperature, high power, high heat dissipation, and high reliability for automotive electronic power device module packaging. Some people believe that silicon nitride ceramic substrates are upgraded products compared to alumina ceramic substrates and aluminum nitride ceramic substrates. Currently, silicon nitride substrates are mainly used for the packaging of Si IGBT and SiC MOSFET, with specific applications as follows:
1. For automotive-grade IGBT, the heat dissipation efficiency is much higher than that of industrial-grade. The internal temperature of the inverter is extremely high, and strong vibration conditions also need to be considered. The performance requirements for automotive-grade IGBT far exceed those for industrial-grade. Silicon nitride substrates are well-suited for automotive-grade IGBT packaging, capable of adapting to high-temperature and high-pressure working environments, effectively dissipating the high heat generated in the power supply system, protecting the chip's normal operation, and extending the service life of electronic devices.
2. For SiC MOSFET, adopting SiC MOSFET devices in the core motor drive of new energy vehicles can increase the range by 5% to 10% compared to traditional Si IGBT. SiC MOSFET chips have a small area and high heat dissipation requirements. Silicon nitride ceramic substrates possess excellent heat dissipation capability and high reliability, making them almost a mandatory choice for the primary application of SiC MOSFET in the field of new energy vehicles. For example, the Tesla Model 3 extensively utilizes silicon nitride ceramic substrates to address the heat dissipation issues of SiC MOSFET devices.
In summary, the two main application directions of silicon nitride ceramics in the field of new energy vehicles are silicon nitride bearings and high thermal conductivity silicon nitride substrates. Silicon nitride bearings exhibit excellent mechanical properties and wear resistance, making them suitable for high-speed rotation and harsh operating conditions, and they have been widely used in the motor systems of new energy vehicles. Silicon nitride ceramic substrates possess high thermal conductivity and mechanical strength, meeting the requirements of high temperature, high power, high heat dissipation, and high reliability for automotive electronic power device modules, and they are extensively employed in the packaging of Si IGBT and SiC MOSFET. These applications contribute to the development of new energy vehicles, enhancing their performance and reliability.
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