Silicon materials dominate, and compound semiconductors are rapidly growing in demand in the fields of radio frequency and power. At present, more than 95% of chips and devices in the world use silicon as the base material. Due to the great cost advantage of silicon materials, silicon will still occupy a dominant position in the field of various discrete devices and integrated circuits in the future. However, the unique physical characteristics of compound semiconductor materials give them unique performance advantages in the fields of radio frequency, optoelectronics, and power devices.

GaAs dominates sub-6G 5G mobile phone radio frequency

Specifically, GaAs occupies a dominant position in the field of 5G mobile phone radio frequency and optoelectronics. GaAs is the most mature compound semiconductor. It has a higher saturated electron velocity and electron mobility, making it suitable for high-frequency applications, and has lower noise during high-frequency operation; at the same time, because GaAs has a higher impact than Si Therefore, gallium arsenide is more suitable for high-power applications. Because of these characteristics, gallium arsenide will still be the main material for mobile phone radio frequency devices such as power amplifiers and radio frequency switches in the 5G era of sub-6G. According to the Qorvo report, the number of radio frequency switches in 5G mobile phones has increased from 10 to 30 in 4G mobile phones, and the average stand-alone value of power amplifiers has increased from US$3.25 to US$7.5 in 4G mobile phones, all of which have driven the growth of the gallium arsenide device market. Another advantage of GaAs is the direct energy gap material, so optoelectronic devices such as VCSEL lasers can be made. Driven by applications such as data center optical modules, mobile phone front VCSEL 3D sensing, and rear LiDAR lidar, optoelectronic devices are the growth of gallium arsenide devices. Another important driving factor for

The great development of GaN in 5G macro base station radio frequency PA

Compared with the previous two generations of semiconductor materials of Si and GaAs, GaN and SiC are both wide-bandgap semiconductor materials. They have the characteristics of high breakdown electric field strength, high saturated electron drift speed, high thermal conductivity, and low dielectric constant. The characteristics of low loss and high switching frequency are suitable for the production of high-frequency, high-power, small-volume and high-density integrated electronic devices. The market application of GaN is biased towards the field of microwave devices, high frequency and small power (less than 1000V) and lasers. Compared with silicon LDMOS (lateral double diffused metal oxide semiconductor technology) and GaAs solutions, GaN devices can provide higher power and bandwidth, and GaN chips will make a leap in power density and packaging every year, and they can be better adapted to Massive MIMO technology, GaNHEMT (High Electron Mobility Field Effect Transistor) has become an important technology for 5G macro base station power amplifiers. At present, GaN on macro base stations mainly uses SiC substrate (GaN on SiC). Because SiC is used as a substrate material and GaN has a small lattice mismatch rate and thermal mismatch rate, and at the same time, it has high thermal conductivity and is easier to grow. The high-quality GaN epitaxial layer can meet the high-power applications of macro base stations.

The silicon carbide solution for electric vehicles brings four major advantages. At present, the components related to power devices in the system architecture of electric vehicles (not including 48V MHEV) include: the main inverter in the motor drive system, the on-board charger (OBC), and the power conversion system (on-board DC-DC). ) And off-board charging piles. The use of silicon carbide solutions for electric vehicles can bring four major advantages:

1. It can increase the switching frequency and reduce energy consumption. Using the all-silicon carbide solution, the switching loss of the inverter is reduced by 80%, and the energy consumption of the whole vehicle is reduced by 5%-10%;

2. The overall module size of the power system can be reduced. Taking the silicon carbide PCU developed by Toyota as an example, its volume is only one-fifth of the traditional silicon PCU;

3. Under the same battery life, use a smaller battery, reduce the use of passive components, and reduce the overall material cost. Taking the 6.6kW bidirectional OBC of an electric vehicle as an example, a typical AC/DC part includes four 650 VIGBTs, several diodes, and a 700-µH inductor, which accounts for more than 70% of the bill of materials cost. By using four 650V SiC MOSFETs, only 230µH inductance is required. This reduces the bill of materials cost by nearly 13% compared to IGBT-based designs.

4. Shorten the battery charging time. Due to the higher charging power and smaller battery, the electric vehicle charging time can be greatly shortened.

The demand for silicon carbide for electric vehicle inverters, OBC, and high-power charging piles will increase substantially. The inverter obtains torque and speed commands from the vehicle controller (VCU), and obtains high-voltage direct current from the battery pack, and converts it into a sine wave alternating current with a controllable amplitude and frequency to drive the motor to make the vehicle run. In electric vehicles, inverters and motors have replaced the roles of traditional engines. Therefore, the design and efficiency of inverters are very important, and their quality directly affects the power output performance of the motors and the endurance of electric vehicles. Due to the excellent characteristics of silicon carbide, the power density of automotive inverters is further increased around SiC MOSFETs, and the weight and cost of the motor drive system are reduced, which has become the focus of the layout of various car companies.

SiC MOSFETs are used in the main drive inverters, each motor uses 24 SiC MOS single-tube modules, each of which is disassembled and packaged has 2 SiC bare crystals, with a withstand voltage of 650V, and the supplier is STMicroelectronics. The high-performance four-wheel drive version of Han EV launched by BYD in 2020 is the first domestic electric vehicle to apply self-developed SiC module in the main inverter. Compared with the current 1200V silicon-based IGBT module, it adopts the SiC solution under NEDC operating conditions. The control efficiency is increased by 3%-8%. It is expected that by 2023, BYD will achieve a full replacement of silicon-based IGBTs with SiC automotive power semiconductors in its electric vehicles. In 2021, Weilai's first pure electric car will also be equipped with a second-generation electric drive platform using silicon carbide modules.

In addition to inverters, silicon carbide has been widely used in OBC. At present, more than 20 car manufacturers use SiC devices in OBC. With the increase in the power of on-board chargers, silicon carbide solutions have also shifted from diodes to " Diode + SIC MOS" evolution; DCDC converters have switched from silicon-based MOS to SiCMOS solutions in 2018. For charging piles, using silicon carbide modules, the power of the charging module can reach more than 60kW, while the design of using MOSFET/IGBT single tube is still at the level of 15-30kW. Compared with silicon-based power devices, the use of silicon carbide power devices can greatly reduce the number of modules. Therefore, for urban high-power charging stations and charging piles, the small volume brought by silicon carbide has advantages in specific scenarios.

In addition to electric vehicles, photovoltaic inverters are another rapidly growing application area for silicon carbide. Using SiC MOSFET or SiC MOSFET combined with SiC SBD power module photovoltaic inverter, the peak energy conversion efficiency can be increased from 96% to more than 99%, the energy loss of the inverter is reduced by more than 50%, and the cycle life of the equipment is increased by 50 times. Thereby, the system volume can be reduced and the service life of the device can be prolonged. High efficiency, high power density, high reliability and low cost are the future development trends of photovoltaic inverters. With the optimization of the cost of solar inverters, in string and centralized photovoltaic inverters, more and more manufacturers will use SiC MOSFET as the main inverter device to replace the original three-level inverter Complex circuit for control.