What is Wide Bandgap (WBG)?
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What is Wide Bandgap (WBG)?

In the field of semiconductor materials, the first generation of semiconductors is Si, the second generation is GaAs, and the third generation of wide energy gap semiconductors refers to SiC and GaN.
Published: Jun 21, 2022
What is Wide Bandgap (WBG)?

Development of the Semiconductor Industry:

The development of the semiconductor industry has gone through three stages so far. The first generation of semiconductor materials is represented by Si, and the second generation of semiconductor materials, GaAs, has been widely used in various electronic devices. Compared with the first- and second-generation semiconductor materials, the third-generation semiconductor materials, also known as wide energy gap semiconductors, have a larger energy gap (> 2.2eV) and are called wide energy gap (WBG) semiconductors, including SiC, AlN, GaN, diamond, ZnO, among which, the more mature ones are SiC and GaN. The third generation of semiconductor materials is causing a revolution in clean energy and a new generation of electronic information technology. Whether it is lighting, household appliances, consumer electronic equipment, energy vehicles, smart grids, or military supplies, all of them have a high-performance semiconductor material. The huge demand, the recent ferment of international energy and environmental protection issues, and the development of high-efficiency and highly integrated power electronics applications have driven the rapid development of the wide-bandgap semiconductor market.

Why Develop the Third Generation Wide Band Gap (WBG)?

Due to the increasingly serious environmental problems caused by global warming and carbon emissions in recent years, human beings take energy conservation, carbon reduction, and caring for the earth as the common primary development direction, is also gradually aiming at high energy efficiency and low energy consumption.

The United Nations has announced that to achieve the goal of keeping global warming within 2°C. Based on current economic trends, CO2 emissions will increase by 21% even if warming is kept within 2°C in 2050, and up to 50% additional electricity must be obtained for various human activities. Therefore, greatly improving and improving the existing energy is the trend in the manufacturing industry.

With the official introduction of carbon neutrality and net-zero regulations in various countries, energy-saving and carbon reduction are no longer just slogans. Global companies must also start to review their energy-saving and environmental protection-related measures as soon as possible, otherwise, it will affect future product sales and the company's sustainable business opportunities. The manufacturing process and use of semiconductor components and electronic products consume a lot of electricity. Even the semiconductor component manufacturing process requires not only electricity but also a large amount of clean water, which consumes a lot of water and electricity resources. In the future, it is bound to develop in the direction of energy conservation, sustainable development, and green environmental protection. The automotive industry has vigorously promoted the development of electric vehicles (EVs), and the use of renewable and alternative energy sources has gradually become a key player in the power sector. Semiconductor and electronic product-related manufacturers are also working to reduce carbon emissions and achieve carbon neutrality. To help the industry achieve these goals, compound semiconductors, especially wide-bandgap (WBG) devices.

The semiconductor raw materials are mainly based on the production of the first generation of Si wafers. However, the current Si-based products, because the physical properties of the material have reached the limit, can no longer increase the power, reduce the heat loss, and increase the speed. Therefore, it is necessary to evolve towards other materials that can better exert electron transmission efficiency and low energy consumption, and the third-generation Wide Band Gap (WBG) semiconductors with high energy efficiency and low energy consumption are developed in this regard.

What is Band Gap?

The theory of quantum physics is used to briefly explain that the division of Band is mainly the Valence Band (VB) in the low energy band and the Conduction Band (CB) in the high energy band. Between VB and CB is a so-called Band Gap (BG).

Metal materials can conduct electricity mainly because the electrons are in the high-energy CB region, and the electrons can flow freely. At room temperature, the main electrons of semiconductor materials are in the low-energy VB region and cannot flow. When heated or obtains energy larger than the energy gap (BG), the electrons in the VB can overcome this energy barrier and transition to CB to form conductive properties.

Therefore, the Transistor element in the integrated circuit can quickly turn on and off the power supply when a small voltage is applied. For a long time, this Si material with a small energy gap (BG) has been widely used until now. However, when the operating temperature is higher than 100 °C, the product is prone to degradation or even failure, and cannot be used in more severe environments, such as the use of tools such as transportation, military, or space. Generation of Wide Band Gap (WBG) materials.

Power is a proportional relationship between Current and Voltage. In the use of Power devices, the energy gap of the first-generation semiconductor material Si is 1.12eV, and the second-generation semiconductor communication material GaAs is 1.43eV, both of which have been widely used in life. Use for two to thirty years. However, the temperature, frequency, and power used by such low-energy-gap materials cannot be broken through, and more suitable materials must be found to replace them. The third-generation Wide Band Gap semiconductor (WBG) material can increase higher operating voltage, generate more power, and reduce energy loss. In addition, the volume can be greatly reduced compared to silicon components.

Technical Advantages of Wide Bandgap Components:

Thermal conductivity is another physical property that affects high power conversion and motor drive applications. The heat generated in the component needs to be conducted out as efficiently as possible, and the thermal conductivity index indicates the efficiency of the heat conduction through the material itself. In this metric, gallium nitride conducts heat slightly lower than silicon, but silicon carbide conducts heat three times as efficiently, making it ideal for high-temperature applications.

Another important feature of wide-bandgap compound semiconductors is that their on-resistance is significantly lower than that of silicon MOSFETs, which can reduce switching losses in power conversion applications, where other switching losses occur in power converters. Relevant passive components are used, such as inductors, transformers, and capacitors.

Furthermore, the physical structure of SiC and GaN components is smaller and lighter than their silicon counterparts, allowing for more compact and lightweight semiconductor components. Due to the smaller die size, the effect of the internal capacitance of the components is reduced, which in turn allows for higher switching frequencies. At the same operating voltage range, the die area of silicon-based MOSFETs is about five times that of SiC MOSFETs. With the above advantages, wide bandgap semiconductor devices are suitable for power conversion and motor drive applications. These benefits are interrelated and work together to enable more energy-efficient, compact, and powerful applications. The difference between gallium nitride and silicon carbide also determines which wide-gap material is more suitable for a particular application.

In circuits based on GaN and SiC components, the ability to operate at higher switching frequencies enables the use of smaller inductors and capacitors, further saving PCB space and bill of materials (BoM) costs.

Which are the Better Wide-gap Materials?

The energy gap of SiC-related materials can be greater than 3.0eV, GaN or Ga2O3 is also as high as 3.4eV and 4.9eV, respectively, and Diamond is as high as 5.4eV.

What Products are Wide-gap Materials Used in?

In recent years, GaN products based on Si or SiC have been released one after another. Currently, fast chargers on the market use high-power (such as 60 watts or more) products made of GaN on Si materials. Because the temperature and thermal effect can be greatly reduced, the components can be greatly reduced, and the size of the charger can be more compact and compact. In the future, the application of fast charging sources such as mobile devices and laptops has unlimited potential.

The current high-power products based on silicon-based materials are mostly insulated gate bipolar transistors (IGBTs) or metal oxide semi-field effect transistors (MOSFETs). Although traditional IGBT high-power modules can be applied to more than 100kW, the speed cannot be increased to 1MHz. Although GaN materials can keep up with the speed, the power cannot reach higher than 1kW, and SiC materials must be used.

Application and Characteristics of Semiconductor Materials:

Because GaN components have absolute advantages in totem pole design, GaN is still used in its current major consumer electronics fast charging-related applications, gradually extending its tentacles to the industrial and automotive fields. In industrial-grade applications, GaN enables higher efficiency and higher power density in high-end power systems for servers, storage, and telecommunications equipment. Not only that, but in battery storage and USP inverters, GaN can improve power density and reduce the size of output filters. The servo driver improves the current waveform due to the GaN element, thereby reducing the motor loss and noise.

In virtually any application, high performance means higher power consumption. The CPU performance is doubled, and the power consumption of the hardware device is increased by 71%. The GPU performance is doubled, and the hardware power consumption will increase by 50%. The improvement of GPU, CPU, and memory performance will lead to a rapid increase in the power consumption of the data center, requiring a larger cooling system to reduce heat generation. The more efficient the processor and memory, the more power the hardware device will consume when operating. This also drives the need for power supplies to develop towards higher efficiency and power density, as well as smaller size and high voltage. If GaN is used in data center architectures, whether it is 12V or the emerging 48V architecture, GaN players can enable AC/DC power supplies not only to obtain the best efficiency but also to reduce the size to the smallest High energy density with the lowest cost per density. Compared with systems built with silicon-based components, the GAN power supply can fit 34 servers in the same data center rack size, requiring six power supplies to power it. However, silicon-based components can only fit into 30 servers, requiring 10 power supplies.

GaN components can conduct electrons more efficiently than silicon components, can withstand higher electric fields, and exceed the performance of silicon components in terms of speed, temperature, and power, so they have been introduced into a variety of automotive and industrial-related applications, such as motors. Controllers, DC/DC converters and LiDAR, in-vehicle OBC systems, etc. In the areas of motor control and DC/DC conversion, the roadmap for the future calls for higher power densities. For lidar applications, however, faster speeds need to be achieved.

In all the above applications, strategic integration of the functions and properties of GaN and silicon components is required. Why do you need integration? Integration can bring many benefits, including efficiency, cost, size and weight, EMI, etc., which are not achieved by traditional silicon MOSFETs. In addition, integrated eGaN transistors behave similar to silicon power MOSFET components, so power system engineers can leverage past design experience with minimal additional training to take advantage of GaN components. Wide energy gap components are used in 5G communication infrastructure, green data centers, electric vehicles and charging piles, and medical and other fields.

The high breakdown electric field characteristics of wide-gap semiconductor materials also bring challenges to the reliability of power crystals. To reduce the electric field strength to improve the reliability of the device, it is necessary to reduce the thickness of the gate oxide insulating layer to reduce the channel resistance value. Therefore, the structure of the wide-bandgap power device will be developed from a planar type to an asymmetric trench type or a double trench type.

Since the channel resistance is closely related to the distribution of the diffusion layer, it is a very important task for the power crystal design engineer to obtain information about the diffusion layer. Diffusion layer analysis method using advanced field emission scanning electron microscopy (FESEM) to provide high precision, high resolution, and high stability results. Through cross-sectional structure observation, diffusion layer analysis, and tools such as SE, CL, and TEM, the microstructure and defect analysis methods of material defects can be quickly identified, helping developers to have a clearer understanding of the wide energy gap in semiconductor materials.

Will SiC and GaN replace silicon components in the future? The industry expects that the three will coexist. Silicon, SiC, and GaN have their unique advantages that cannot be replaced by any material at present. For example, silicon-based components have a low unit price and large production volume. Therefore, when choosing which component to use, suitable semiconductor materials should be found from the needs of the application.

New Challenges for Derived Testing of New Materials

Under the global trend of promoting environmental protection and energy-saving, wide-bandgap semiconductors have become prominent for a while to allow the industry to smoothly respond to the various regulations that follow. It also brings new challenges to power semiconductor testing. Due to the characteristics of high electron mobility and high breakdown voltage, it is more suitable for operation at high power and high frequency, so wide energy gap semiconductors are one of the important trends in future semiconductors. From the changes in the internal junction temperature of SiC and GaN power modules, as well as in various applications, modules, devices, converters, and other levels, the changes brought about by the adoption of SiC and GaN will lead to a new technical challenge. Therefore, the effective testing of power components and systems made of wide-bandgap semiconductors such as SiC and GaN will be the key to the success of the industry in the market.

Wide-bandgap semiconductor power devices involve multiple measurements, including on-state, off-state, capacitive voltage, and dynamic characteristics, and require voltage and current bias, as well as voltage and current measurements to fully reveal the state and characteristics of the device. In addition to dynamic characteristics, key static parameter testing is important to avoid problems in the entire system. Therefore, in addition to choosing the right test instrument, professional testing software is also required to comprehensively verify whether the system created by wide-bandgap semiconductor components is foolproof.

Published by Jun 21, 2022 Source :technews

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