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Third-generation semiconductor materials: silicon carbide

Addtime:2020-02-03 Click:

Because of its stable chemical properties, high thermal conductivity, small thermal expansion coefficient, and good abrasion resistance, silicon carbide has many other uses besides abrasives. For example, it can be used to apply silicon carbide powder to the turbine wheel The inner wall can improve its abrasion resistance and extend its service life by 1-2 times. The advanced refractory material used is made of heat-resistant, small size, light weight and high strength, and has good energy saving effect. Low-grade silicon carbide (containing about 85% of SiC) is an excellent deoxidizer. It can accelerate the speed of steelmaking, facilitate the control of chemical composition, and improve the quality of steel. In addition, silicon carbide is also widely used to make silicon carbide rods for electric heating elements.
Third-generation semiconductor materials: silicon carbide
The hardness of silicon carbide is very high, Mohs hardness is 9.5, second only to the hardest diamond in the world (10), it has excellent thermal conductivity, is a semiconductor, and can resist oxidation at high temperatures.
Silicon Carbide History Table
The first discovery of silicon carbide in a meteorite in 1905
The first silicon carbide crystal light-emitting diode was born in 1907
A major breakthrough in theory and technology in 1955, LELY proposed the concept of growing high-quality carbonization, and since then SiC has been an important electronic material
The first world silicon carbide conference was held in Boston in 1958 for academic exchange
In the 1960s and 1970s, silicon carbide was mainly studied by the former Soviet Union. Grain purification growth method using "LELY improved technology" for the first time by 1978
1987——Since the establishment of the silicon carbide production line based on the research results of CREE, suppliers have begun to provide commercial silicon carbide based.
In 2001, German company Infineon introduced SiC diode products, followed by Cree and STMicroelectronics. In Japan, ROHM, Shinnippon Wireless and Renesas Electronics have started production of SiC diodes.
On September 29, 2013, the International Society of Silicon Carbide Semiconductors “ICSCRM2013” ​​was held. Semiconductor companies, research institutes and other institutions from 24 countries participated in the conference, with 794 participants, the highest number in history. Internationally renowned semiconductor device manufacturers, such as Cree, Mitsubishi, ROHM, Infineon, Fairchild, etc., exhibited the latest mass-produced silicon carbide devices at the conference.
Until now, many manufacturers have produced silicon carbide devices such as Cree, Microsemi, Infineon, and Rohm.
Advantages of SiC devices
Silicon carbide (SiC) is currently the most mature wide-gap semiconductor material. Countries around the world attach great importance to the research of SiC, and have invested a lot of manpower and material resources to develop actively. Research planning, and some international electronics giants have also invested heavily in the development of silicon carbide semiconductor devices.
Compared with ordinary silicon, components using silicon carbide have the following characteristics:
1.High voltage characteristics
Silicon carbide devices withstand 10 times the voltage of equivalent silicon devices
Silicon carbide Schottky tube withstand voltage up to 2400V.
The silicon carbide field effect tube can withstand tens of thousands of volts, and the on-state resistance is not very large.
2.High frequency characteristics
3.High temperature characteristics
Today, Si materials are close to their theoretical performance limits. SiC power devices have been expected to be “ideal devices” because of their high withstand voltage, low loss, and high efficiency. However, compared with the previous Si material devices, the balance between performance and cost of SiC power devices and their high-tech requirements will become the key to whether SiC power devices can be truly popular.
At present, low-power silicon carbide devices have entered the practical device production stage from the laboratory. At present, the price of silicon carbide wafers is relatively high, and its defects are also many.
Most Concerned Silicon Carbide MOS
Classification of SiC devices
SiC-MOSFET is the most concerned device in the research of silicon carbide power electronic devices. The outstanding results are Cree in the United States and ROHM in Japan.
Structure of silicon carbide MOS
The silicon carbide MOSFET (SiCMOSFET) N + source region and P well doping are both ion implanted and annealed at 1700 ° C. Another key process is the formation of silicon carbide MOS gate oxides. Since both Si and C atoms are present in the silicon carbide material, a very special gate dielectric growth method is required. The advantages of its trench star structure are as follows:
Flat vs groove
SiC-MOSFET uses trench structure to maximize the characteristics of SiC
Advantages of silicon carbide MOS
Silicon IGBTs can only work at frequencies below 20kHz. Due to material limitations, high voltage and high frequency silicon devices cannot be realized. Silicon Carbide MOSFET is not only suitable for a wide voltage range from 600V to 10kV, but also has the excellent switching performance of unipolar devices. Compared to silicon IGBTs, silicon carbide MOSFETs have lower switching losses and higher operating frequencies in the absence of current tails in the switching circuit.
The loss of a 20kHz silicon carbide MOSFET module can be half that of a 3kHz silicon IGBT module, and a 50A silicon carbide module can replace a 150A silicon module. Shows the huge advantages of silicon carbide MOSFETs in operating frequency and efficiency.
The silicon carbide MOSFET parasitic body diode has extremely small reverse recovery time trr and reverse recovery charge Qrr. As shown in the figure, for a device with a rated current of 900V, the reverse charge of a parasitic diode of a silicon carbide MOSFET is only 5% of that of a silicon-based MOSFET of the same voltage specification. For the bridge circuit (especially when the LLC converter is operating above the resonance frequency), this index is very critical. It can reduce the loss and noise caused by the dead time and the reverse recovery of the body diode, which is convenient to improve Switching frequency.
Application of silicon carbide MOS tube
The silicon carbide MOSFET module has huge advantages in the application of photovoltaic power, wind power, electric vehicles and rail transit in high-power power systems. The advantages of high voltage, high frequency and high efficiency of silicon carbide devices can break through the limitations of existing electric vehicle motor designs due to device performance. This is the focus of research and development in the field of electric vehicle motors at home and abroad. For example, the electric power control unit (PCU) in the hybrid electric vehicle (HEV) and pure electric vehicle (EV) jointly developed by Denso and Toyota uses silicon carbide MOSFET modules, and the volume ratio is reduced to 1/5. The EV motor drive system developed by Mitsubishi uses a SiCMOSFET module, and the power drive module is integrated into the motor, achieving integration and miniaturization goals. It is expected that from 2018 to 2020, silicon carbide MOSFET modules will be widely used in electric vehicles at home and abroad.
SiC Schott diode
1.Silicon carbide Schottky diode structure
The silicon carbide Schottky diode (SiCSBD) device uses a junction barrier Schottky diode structure (JBS), which can effectively reduce reverse leakage current and has better high voltage capability.
2. Advantages of SiC Schottky diodes
SiC Schottky diode is a unipolar device, so compared with the traditional silicon fast recovery diode (SiFRD), SiC Schottky diode has ideal reverse recovery characteristics. When the device is switched from forward to reverse blocking, there is almost no reverse recovery current (see Figure 1.2a). The reverse recovery time is less than 20ns, and the reverse recovery time of the 600V10A SiC Schottky diode is 10ns. Within. Therefore, SiC Schottky diodes can work at higher frequencies and have higher efficiency at the same frequency. Another important feature is that silicon carbide Schottky diodes have a positive temperature coefficient, and the resistance gradually rises as the temperature rises, which is exactly the opposite of silicon FRD. This makes the silicon carbide Schottky diodes very suitable for parallel and practical use, which increases the safety and reliability of the system.
The main advantages of SiC Schottky diodes are summarized as follows:
1. Almost no switching loss
2. Higher switching frequency
3. Higher efficiency
4. Higher working temperature
5.Positive temperature coefficient, suitable for parallel operation
6. Switching characteristics are almost independent of temperature