What is Wide Bandgap (WBG)?

Development of the Semiconductor Industry:

The semiconductor industry has gone through three stages of development so far. The first and second generation of semiconductors, which use Si and GaAs semiconductor materials as their base, have been widely used in various electronic devices. The third-generation of semiconductors use materials that have a larger energy gap than Si and GaAs, and are therefore called wide energy gap (WBG) semiconductors. These include semiconductors that use SiC, AlN, GaN, diamond, or ZnO as their base material. Among these, the more mature ones are SiC and GaN. The third generation of semiconductor materials is causing a revolution in clean energy and electronic information technology development. Whether it is in lighting, household appliances, consumer electronic equipment, energy vehicles, smart grids, or military supplies, all are made of high-performance semiconductor material. The huge demand, the international concern for 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 increasing environmental problems caused by global warming and carbon emissions, people are taking energy conservation, carbon reduction, and caring for the earth as a common goal, aiming to gradually increase energy efficiency and reduce energy consumption.

The United Nations has announced a goal of keeping global warming to within 2°C. It is also expected that electricity demand will increase by up to 50%. Therefore, to meet this goal, improving energy production and use is an important 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. Besides electricity, it also uses a large amount of clean water. In the future, more attention will be paid to 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 are being actively developed.

What is Band Gap?

The Band Gap (BG) is a reference to the division of the bands that an electron can occupy in an atom. In the Valence Bands (VB) the electrons are in a low energy band and cannot migrate to adjacent atoms. When energy is applied to the material, the electrons jump to a higher level energy band, called the Conduction Band, (CB) where can migrate to adjacent atoms. The energy difference between the VB and CB is the 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 enough heat or energy is applied, the electrons in the VB can overcome this energy gap barrier and transition to the CB to create conductive properties.

TTherefore, 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 the most widely used. However, when the operating temperature is higher than 100 °C, the product is prone to degradation or even failure. Therefore, they cannot be used in more severe environments, such as encountered in transportation, military, or space applications.

First-generation semiconductor material Si has a band gap of 1.12eV. Second generation GaA’s band gap is 1.43eV. While both have been widely used, their low-energy-gap has limited their use in higher frequency applications, or with higher voltages where heat can generate higher temperature operating conditions. More suitable materials were needed to replace them. Newly developed, third-generation, Wide Band Gap semiconductor (WBG) materials can be used with higher operating voltages and they reduce energy loss. Their size has also been 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. While gallium nitride conducts heat slightly slower than silicon, 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. This makes them highly suitable for use in inductors, transformers, and capacitors.

The physical structure of SiC and GaN components is smaller and lighter than their silicon counterparts, allowing for more compact and lightweight semiconductor components. At the same operating voltage range, the size of the die area required for silicon-based MOSFETs is about five times that of SiC MOSFETs. Due to the smaller size, the effect of the internal capacitance of the components is reduced, which in turn allows for higher switching frequencies.

By using GaN and SiC components, circuits can operate at higher switching frequencies enabling the use of smaller inductors and capacitors, further saving PCB space and material costs.

Which are the Better Wide-gap Materials?

The energy gap of SiC-related materials can be greater than 3.0eV. GaN or Ga2O3 have energy gaps of 3.4eV and 4.9eV respectively, and Diamond’s energy gap is 5.4eV.

What Products are Wide-gap Materials Used in?

In recent years, multiple GaN products based on Si or SiC have been released. Fast chargers used for high-power (60 watts or more) products are made of GaN on Si materials. Because the thermal effect is greatly reduced, their size can be significantly reduced, making the charger more compact. In the future, the application of fast charging devices for items such as mobile devices and laptops has unlimited potential.

Currently, high-power products made with 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 applications with more than 100kW, their speed cannot be increased beyond 1MHz. Although GaN materials can meet the speed requirements, the power cannot exceed 1kW, so SiC materials must be used.

Application and Characteristics of Semiconductor Materials:

GaN is widely used in major consumer electronics which require fast charging, and is gradually extending its use to the industrial and automotive fields. In industrial-grade applications, GaN is used in high-end power systems for servers, storage, and telecommunications equipment. In battery storage and USP inverters, GaN can improve power density and reduce the size of output filters. In servo drivers they improve motor power and reduce noise.

In virtually any application, high performance means use under higher power consumption. The performance of CPUs is doubled, and the power capacity of the hardware device is increased by 71%. The GPU performance is doubled, and the hardware power capacity can 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 dissipate the heat generated. This also drives the need for power supplies to develop higher efficiency and power density, as well as smaller size and higher voltages. Where a silicon-based power supply would only fit into 30 servers, and require 10 power supplies, a GaN power supply can fit 34 servers and require six power supplies.

GaN components 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. They have been introduced into a variety of automotive and industrial-related applications, such as for motors, controllers, DC/DC converters, LiDAR, on-board charger (OBC) systems, etc. In motor control and DC/DC conversion applications, the future will call for higher power densities, however for LiDAR applications, 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, 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 stations, and medical and other fields.

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

Wide-bandgap semiconductors bring new challenges to power semiconductor testing. Due to the characteristics of high electron mobility, high breakdown voltage, changes in the internal junction temperature, etc. there will be new technical challenges in the testing and quality control of these materials. Therefore, the effective testing of power components and systems made of wide-bandgap semiconductors such as SiC and GaN will be a key to the success of the industry.

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.