Introduction
What is silicon carbide (SiC)?
Compared to the traditional semiconductor material silicon, it has advantages in terms of breakdown field strength, band width, electron saturation rate, melting point and thermal conductivity.
For example, Si-MOSFETs have to be made thicker for the same withstand voltage level, and the higher the withstand voltage the thicker they will be, resulting in higher material costs. There is a voltage isolation zone between the gate and drain, the wider the zone, the greater the internal resistance, the more power loss, and SiC-MOSFETs can be made thinner, reaching 1/10 of the thickness of Si-MOSFETs, while the drift zone resistance is reduced to 1/300 of the original, the on-state resistance is smaller, the energy loss is smaller, and the performance is improved.
The advantages of SiC over Si power devices in diodes and transistors are characterized as follows. In secondary tubes, Si-FRD can be constructed with a voltage of 250V, while the voltage of SiC can reach about 4000V; in transistors, Si-MOSFETs can achieve 900V, and there are also 1500V on the market, but the characteristics will be inferior, while the voltage of SiC products can reach 3300V.
So where do SiC-MOSFETs fit into all the scenarios in which power semiconductors are used? The horizontal axis of the axis below is the switching frequency, and the vertical axis is the output power. It can be seen that the application of SiC-MOSFETs is concentrated in relatively high frequency and high voltage areas, while ordinary Si-MOSFETs are mainly used in low voltage and high frequency areas, and then Si-IGBTs are used in high voltage and low frequency, if the voltage does not need to be very high, but the frequency should be very high to choose GaN HEMT.
Silicon carbide consists of silicon and carbon. Both are periodic IV elements, so they prefer covalent bonding. In addition, each carbon atom is surrounded by four silicon atoms and vice versa. This results in a highly ordered configuration, a single crystal, as in the correct diagram. (The crystal is polarised, which means that we can identify a silicon face and a carbon face, each with one freely bonded atom.) However silicon, or gallium arsenide has only one crystal structure, silicon carbide has several.
There are several stable long-term stacking orders in a large sample. This number corresponds to the number of bilayers of Si and C that precede the repetition of this pattern. For example, 4H repeats ABACABAC, etc. Of these, 4H and 6H are of technical value because large wafers can be fabricated from this material and therefore used for device production. We will discuss manufacturing later.
Power semiconductors occupy a central position in power electronics systems. After decades of development, silicon semiconductors are approaching their theoretical performance limits and are unable to meet the increasingly high performance requirements of converters. Since the 21st century, wide-band semiconductors, mainly Silicon Carbide (SiC), have received increasing attention. The insulating breakdown field of silicon carbide is 10 times stronger than that of silicon, and the drift region resistance can theoretically be reduced to 1/300th of that of silicon at the same withstand voltage, enabling “low on-resistance”, “high switching speed” and “high switching speed” while maintaining “high withstand voltage” capability. high switching speed” and “high switching frequency”. In addition, the band gap width of silicon carbide is three times wider than that of silicon, so that silicon carbide power semiconductor chips can operate stably at high temperatures.
The power chip is connected to the external circuitry through the package and its performance is dependent on the support of the package, which is usually used as a power module in high power applications. The conventional power module package structure is shown in Figure 1. The packaging is adequate to meet the characteristics of silicon semiconductors, but when applied to silicon carbide semiconductors, there are challenges that limit their excellent characteristics. The main challenges in the current silicon carbide power module packaging are in the areas of electrical performance, thermal management of the chip, high temperature operation of the chip and long term reliable insulation.
This paper analyses and summarises the existing packaging methods for silicon carbide power modules in three technical directions: electrical, thermal and insulation, and analyses the challenges and opportunities facing silicon carbide power modules.
The silicon carbide heat exchanger is a new type of heat exchanger that uses silicon carbide ceramic material as the heat transfer medium. As silicon carbide ceramic has excellent characteristics such as corrosion resistance, high temperature resistance, high thermal conductivity, high hardness and wear resistance, silicon carbide ceramic heat exchanger is suitable for high temperature and corrosion resistant environment needs.
Many friends of silicon carbide heat exchanger working principle is not very well understood, today I explain: the development of this device heat exchanger element material is a new silicon carbide engineering ceramics, which has high temperature and thermal shock resistance of excellent performance, from 1000 ℃ air-cooled to room temperature, repeatedly 50 times more than the crack does not appear; thermal conductivity and stainless steel equivalent; in the oxidizing and acidic media with good Corrosion resistance. The thermal compensation has been successfully solved in the structure and the gas sealing problem has been better solved. The device has a high heat transfer efficiency and a significant energy saving effect. It can be used to preheat the combustion air or to heat the process gases of certain processes, saving primary energy and fuel savings of up to 30 % or more, and can strengthen the process and significantly increase production capacity.
