A few days ago, Alibaba Damo Institute predicted the trend of science and technology in 2021. Among them, the third generation semiconductors represented by GaN and SiC will be in a big explosion of applications.

What is the difference between the third generation semiconductor and the first two generations? Why have these two years become the nodes of the outbreak? After the third generation of semiconductors, what materials will take the lead again? The expert was interviewed by the reporter.

[What are the key words to distinguish the "generation of" semiconductors]

Band gap is a key parameter to distinguish different generations of semiconductors. The so-called "band gap" width is the energy difference from the bottom of conduction band to the top of valence band, in EV. The conduction band and valence band of conductor are overlapped, and there is no "forbidden band". The energy at the bottom of conduction band and the top of valence band of semiconductor is staggered, and there is a band gap, just like there is a height difference from the first floor to the second floor. The size of the band gap determines whether the material has the properties of conductor, semiconductor or insulator.

The first generation of semiconductors is represented by silicon with a band gap of 1.12 ev. The main component of sand and rock is silicon, which is second only to oxygen in the crust. Silicon crystal and device processing technology is very mature. Silicon semiconductor IC and discrete devices are widely used. IC of computers, mobile phones, refrigerators and other household appliances all use silicon materials. Automobile, aircraft, aerospace and other fields are inseparable from silicon materials and devices.

The second generation semiconductor is represented by gallium arsenide, whose band gap is 1.42 EV, which is wider than that of silicon. Due to the higher electron mobility and current density of the second generation semiconductor, it is more suitable for microwave devices and is widely used in power amplifiers of mobile phones, base stations and radar systems.

[What are the applicable scenarios of the third generation semiconductor]

As the third generation semiconductors, GaN and SiC have bandgap of 3.39 EV and 3.26 EV, respectively. The higher bandgap is very suitable for high voltage devices. GaN has high electron saturation speed, which is 2.5 times that of Si and 2 times that of GaAs. It is very suitable for microwave devices, such as RF front-end amplifiers in mobile phones, 5g base stations and microwave radars. Microwave radar is not limited to the field of aerospace and national defense, but also has potential application in new energy vehicle automatic driving in the future. It can be used to accurately sense obstacles and guide automatic driving data adjustment in time.

In addition, GaN can also be used as a power switching device. The faster the switching speed is, the smaller the power conversion system can be and the lower the power consumption can be. There is a power switch device in the mobile phone charger, which can convert 220V AC into 5V DC, and then charge the mobile phone. "GaN power switch devices are the most popular small fast chargers now, and they are expected to be used in wireless chargers in the future."

However, GaN has its own limitations, which requires heteroepitaxial growth on sapphire, silicon, SiC and other substrates. Due to different materials, the mismatch of thermal expansion coefficient and lattice constant will result in high defects in heteroepitaxial materials. At present, GaN microwave devices are based on SiC substrate epitaxial GaN technology, the breakdown voltage is generally about 600v.

At this time, the advantages of SiC appear. SiC crystal can grow homogeneously on SiC substrate with low defect density, which can give full play to the high voltage resistance of SiC, and the device voltage resistance can easily reach 1200v-1700v. SiC power switch devices are suitable for high temperature, high voltage and high power applications. In the future, they will compete with "silicon-based insulated gate bipolar transistor" in the market. At present, they are mainly used in electric vehicles and charging posts. "SiC has been used in Tesla electric vehicles, and will also be used in the fields of power grid, locomotive traction and aerospace in the future."

The third generation of semiconductors were limited to a small range of applications, why did they become explosive nodes in the past two years? "In fact, China's semiconductor design capability is not weak. For example, Huawei has independently developed 7-nanometer Kirin chips. China's IC industry "short board" is mainly concentrated in raw materials, design software and manufacturing equipment, which leads to the small-size silicon integrated circuit processing is controlled by others. For the third generation semiconductor, the device can be completed by using the existing large-scale device processing platform. For example, the power switch device only needs 0.35μm-0.5μm processing technology, and the manufacturing line can be slightly modified and adjusted. The explosion of the application of the third generation semiconductor can also be regarded as "overtaking on the curve". I hope our country will win the opportunity and be ahead in this respect. " According to reports, both CRRC group and State Grid are building 6-inch silicon carbide production lines.

[What is the 3.5th generation semiconductor]

After the third generation semiconductor, what materials will take the lead again? "The band gap of insulator is so wide that it is difficult to conduct electricity by doping. But in recent years, with the continuous development of technology, some insulators can also be used as semiconductors, so they are considered to be the 3.5th generation semiconductors. "

For example, diamond and AlN have band gaps of 5.45EV and 6.2EV respectively, which are very suitable for power switching devices in extreme environments such as high temperature and high radiation. "However, it is still very difficult and a long way to go to synthesize single crystal and large-size diamonds."

* Jiefang Daily, 2020-12-31