In recent years, domestic and foreign attention to silicon carbide has been increasing!
What is silicon carbide
Silicon carbide is a compound semiconductor material composed of carbon and silicon elements. Silicon carbide (SiC), gallium nitride (GaN), aluminum nitride (ALN), gallium oxide (Ga2O3), etc., because the bandgap width is greater than 2.2eV are collectively referred to as wide bandgap semiconductor materials, also known as the third generation in China semiconductors.
In the semiconductor industry, the materials are divided into: first-generation element semiconductor materials, such as silicon (Si) and germanium (Ge); second-generation compound semiconductor materials: such as gallium arsenide (GaAs), indium phosphide (InP), etc .; The third generation of wide band gap materials, such as silicon carbide (SiC), gallium nitride (GaN), aluminum nitride (ALN), gallium oxide (Ga2O3), etc.
Among them, silicon carbide and gallium nitride are currently the most promising semiconductor materials, and they can be called the next-generation "golden track" in the semiconductor industry.
The first discovery of silicon carbide in history was in 1891. American Acheson discovered a carbon compound when electrolyzing diamond. This was the first time silicon carbide was synthesized and discovered. After a century of exploration, especially after entering the 21st century, human beings have finally sorted out the advantages and characteristics of silicon carbide, and used the characteristics of silicon carbide to make various new devices. The silicon carbide industry has developed rapidly.
Compared with traditional silicon materials, silicon carbide's band gap is 3 times that of silicon; thermal conductivity is 4-5 times that of silicon; breakdown voltage is 8 times that of silicon; and the electron saturation drift rate is 2 times that of silicon.
Various characteristics mean that silicon carbide is particularly suitable for manufacturing high-frequency and high-power devices that are resistant to high temperatures, high voltages, and large currents.
Currently known silicon carbide has about 200 crystal structure forms, cubic dense sphalerite α crystal structure (2H, 4H, 6H, 15R) and hexagonal dense wurtzite β crystal structure (3C- SiC) and so on.
Among them, the β crystal structure (3C-SiC) can be used for manufacturing high-frequency devices and other thin film substrates, for example, for growing a gallium nitride epitaxial layer, manufacturing a silicon carbide-based gallium nitride microwave radio frequency device, and the like. Alpha crystal 4H can be used to make high-power devices; 6H is the most stable and can be used to make optoelectronic devices.
3C-SiC crystal structure
Will silicon carbide replace silicon in the future?
The third-generation semiconductor materials and traditional silicon materials have completely different application fields. Silicon is more used to make traditional integrated circuit chips such as memories, processors, digital circuits, and analog circuits. And silicon carbide is particularly suitable for manufacturing high-power devices, microwave radio frequency devices, and optoelectronic devices because it can withstand large voltages and currents. In particular, after the cost of silicon carbide in the power semiconductor field is reduced in the future, silicon-based MOSFETs, IGBTs, etc. will be replaced to a certain extent. However, silicon carbide will not be used as a digital chip. The two are complementary. In the field of some power devices, silicon carbide chips will have an advantage in the future.
From the application side, it is no exaggeration to call SiC the "golden track".
At present, two kinds of silicon carbide and gallium nitride chips, if you want to make the most of the characteristics of the material itself, the ideal solution is to grow an epitaxial layer on a silicon carbide single crystal substrate. That is, a long silicon carbide epitaxial layer on silicon carbide is used to manufacture power devices; a long gallium nitride epitaxial layer on silicon carbide can be used to manufacture medium and low voltage high frequency power devices (less than 650V), high power microwave radio frequency devices and optoelectronic devices.
Some people can't help asking, long homoepitaxial on silicon carbide can be understood, but why can it be the best heterogeneous substrate for GaN epitaxial wafers? Why doesn't GaN epitaxial wafer use GaN single crystal substrate? In fact, from a theoretical point of view, it is best to use a gallium nitride single crystal substrate, but the gallium nitride single crystal substrate is too difficult to do, and it is difficult to have hundreds of by-products in the reaction process. Control, while the crystal growth efficiency is extremely low, and the area is small, expensive, and does not have any economics. And silicon carbide and gallium nitride have more than 95% lattice fit, performance indicators far exceed other substrate materials, such as sapphire, silicon, gallium arsenide, and so on. Therefore, silicon carbide-based gallium nitride epitaxial wafers become the best choice.
Therefore, the silicon carbide substrate material can meet the needs of the two most promising materials for the substrate material at present, "one material for two uses", so this is the source of the saying that "the silicon carbide has the world".
What are the advantages of silicon carbide?
If only silicon carbide chips are counted, compared with traditional silicon-based power chips, silicon carbide has unparalleled advantages in power semiconductors: silicon carbide can withstand larger currents and voltages, higher switching speeds, and lower energy losses. More resistant to high temperatures. Therefore, the power module made of silicon carbide can correspondingly reduce the components of capacitors, inductors, coils, and heat dissipation components, making the entire power device module lighter, energy-saving, stronger output power, and also enhances reliability. The advantages are obvious.
From the perspective of the terminal application layer, silicon carbide has a wide range of applications in high-speed rail, automotive electronics, smart grids, photovoltaic inverters, industrial electromechanics, data centers, white goods, consumer electronics, 5G communications, and next-generation displays. huge.
In 2015, automotive giant Toyota demonstrated the PCU with a full silicon carbide module. In comparison, the silicon carbide PCU is only one-fifth the volume of traditional silicon PCUs, reducing weight by 35%, reducing power loss from 20% to 5%, and improving the economics of hybrid vehicles by more than 10%, with obvious economic and social benefits. .
In addition, the well-known electric vehicle manufacturer Tesla's Model 3 also announced the use of ST's full silicon carbide module. Both inside and outside the industry have seen the huge application potential of silicon carbide in the future, and they have laid out one after another, so the "golden track" is worthy of the name.
All high-quality girls are not easy to obtain, and it is difficult to make all the good materials.
Everyone knows the huge commercial prospects of silicon carbide in the future, but everyone who joins this industry will encounter the first most realistic problem. What about materials?
At present, the traditional silicon-based industry is extremely mature in the business environment, at least most of the reason is that silicon materials are easier to obtain. The mature and efficient preparation technology of silicon materials makes silicon materials currently very cheap.
At present, using a straight-draw method, a silicon single crystal rod of about 2-3 meters can be grown in 72 hours, and a single crystal rod can cut thousands of silicon wafers at a time.
Do you know how thick silicon carbide single crystal can grow in 72 hours? It's only a few centimeters away.
At present, the fastest silicon carbide single crystal growth method has a growth rate of about 0.1mm / h-0.2mm / h, so there are only 7.2mm to 14.4mm thick crystals in 72 hours.
So the current cost of silicon carbide single wafer is still very high.
As the world's leading silicon carbide company, Cree in the United States has almost monopolized more than 70% of production capacity, so downstream manufacturers at home and abroad have signed long-term contracts with Cree to lock up production capacity.