As Tesla took the lead in using a large number of silicon nitride ceramic substrates in Model 3 SIC MOSFET devices to solve the module heat dissipation problem, silicon nitride ceramic materials have once again entered the industry’s sight. With the recent vigorous promotion of 800V high-voltage fast charging technology by new energy vehicles, the problem of electrical corrosion of steel ball bearings in traditional drive motors has attracted attention. Tesla has adopted hybrid ceramic bearings from Japan’s NSK in the output shaft of the motor. The bearing balls are composed of 50 silicon nitride bearing balls. Silicon nitride bearings are also highly valued by mainstream car manufacturers.
01 Silicon nitride ceramics are engineering materials with excellent performance
1) Introduction to silicon nitride ceramics
Silicon nitride (Si₃N₄) is a compound synthesized under artificial conditions by combining nitrogen and silicon. The crystal phase is mainly divided into needle-shaped crystals of α-silicon nitride and granular crystals of β-silicon nitride. It has excellent electrical, thermal, and mechanical properties and can be used up to 1400℃ in an oxidizing atmosphere and up to 1850℃ in a neutral or reducing atmosphere.
The upstream materials of silicon nitride are mainly silicon powder and nitrogen. The process flow of preparing silicon nitride ceramic products generally includes raw material processing, powder synthesis, powder processing, forming, green body processing, sintering, and ceramic body processing.
The quality of silicon nitride ceramics includes technical indicators such as volume density, open porosity, hardness, elastic modulus, flexural strength, impact strength, thermal expansion coefficient, thermal conductivity, resistivity, etc. Different scenarios may also focus on its chemical composition, phase ratio, and microstructure morphology.
2) Silicon nitride ceramics have outstanding mechanical and thermal properties
Silicon nitride ceramics have the advantages of hardness, heat resistance, wear resistance and corrosion resistance of general ceramic materials, and have the advantages of good thermal shock resistance, high temperature creep resistance, good self-lubrication and good chemical stability. It also has relatively low density and excellent dielectric properties, such as dielectric constant and dielectric loss.
Compared with the current mainstream high-temperature ceramic materials, it has better heat shock resistance and higher strength than alumina ceramics; higher high-temperature strength and hardness than zirconium oxide; and similar performance to silicon carbide, but the fracture toughness is nearly twice that of silicon carbide.
3) Silicon nitride is widely used in new energy, chemical industry, aerospace and other fields
Taking advantage of silicon nitride’s high hardness, high wear resistance, high strength, light weight and self-lubrication, in the fields of mechanical processing and new energy vehicles, silicon nitride ceramics can be made into high-speed turning tools, bearings (balls), valves, guide blades and turbine blades of gas turbines, pipelines, grading wheels and ceramic tools, etc.
Taking advantage of silicon nitride’s non-magnetic, high insulation, wave transmission, low dielectric loss and high thermal conductivity, in the fields of electronics and new energy vehicles, silicon nitride ceramics can be made into high thermal conductivity substrates, filters, mobile phone antennas, etc.
Taking advantage of silicon nitride’s corrosion resistance, high temperature resistance, erosion resistance and unchanged performance at high temperature, in the chemical industry, silicon nitride ceramics can be made into ball valves, pump bodies, sealing rings, filters, heat exchanger components, and fixed catalyst carriers, etc.
Taking advantage of silicon nitride’s high hardness, high strength, wave transmission, and light weight, silicon nitride ceramics can be made into electronic wearable shells in the consumer field.
02 Mainstream application products of silicon nitride
The rapid growth of downstream demand for new energy, energy storage,e and new energy vehicles will further promote the rapid growth of the domestic silicon nitride structural parts (such as silicon nitride ceramic balls, silicon nitride valve balls and silicon nitride grading wheels) and silicon nitride ceramic substrates and other mainstream application product markets.
1. Silicon nitride ceramics are the application trend for future bearings
According to statistics, the automotive bearing market is still dominated by traditional steel bearings. Silicon nitride ceramic bearings have a broad replacement space as new application materials in the future. Rolling bearings are composed of rings, rolling elements, retainers, grease, and seals. Silicon nitride full ceramic ball bearings refer to rolling elements and rings made of silicon nitride materials. Under the wave of electrification, steel ball bearings are currently facing the problem of being unable to break through the limitation of higher speed requirements, unable to meet the user’s demand for low noise in the whole vehicle, and electrical corrosion under higher voltage and high switching frequency requirements. Compared with traditional steel balls and other ceramic materials, silicon nitride ceramics have the characteristics of lightweight, high hardness and heat resistance, low friction, corrosion resistance, self-lubrication, etc., and are regarded as the best material for manufacturing ceramic bearings in the future.
2. Silicon nitride ceramic substrate is the ceramic substrate material with the best comprehensive performance
As the power density of IGBT and third-generation semiconductor power devices increases, the mainstream alumina substrate with low thermal conductivity, low mechanical strength, poor toughness, high dielectric constant, and high thermal expansion coefficient can no longer meet the needs of the new energy vehicle market. Silicon nitride ceramics are considered to have the best comprehensive performance ceramic substrate material due to their excellent mechanical strength, good chemical stability, and thermal shock resistance. At the same time, with a thermal expansion coefficient close to that of silicon carbide crystals, the third-generation semiconductor substrate has become the first choice for high thermal conductivity substrate materials for third-generation silicon carbide semiconductor power devices.
Currently, silicon nitride ceramic substrates are widely used in power modules, heat sinks, LEDs, wireless modules, etc., and will continue to grow in the future.