The Third-generation Semiconductor Materials - The Key Technologies of GaN and SiC

What are Third Generation Semiconductors and Wide-bandgap Semiconductors?

In the field of semiconductor materials, the first-generation semiconductor was Si, the second-generation semiconductor was GaAs, and the third-generation semiconductor (Wide-bandgap semiconductors, WBG) has been SiC and GaN. The stability and consistency of a semiconductor will depend on its “energy gap,” which refers to the minimum energy required to make a semiconductor switch form its insulation state to its conduction state. The silicon and gallium arsenide used for the first and second-generation semiconductors had low energy gaps with values of 1.12 eV and 1.43 eV respectively. The energy gaps of third generation wide-bandgap semiconductors, SiC and GaN have energy gaps of 3.2 eV and 3.4 eV respectively. With the higher energy gap, when the semiconductor encounters high temperature, high voltage, and high current, they will not easily change from the insulating state to the conductive state, so will have more stable characteristics and better energy conversion then earlier semiconductor materials.

Third-generation semiconductor materials are used in the Wide-bandgap semiconductors (WBG) power components widely used in 5G base stations, low-orbit satellites, electric vehicles, mobile phone fast charging, and other applications. Taiwan's semiconductor industry has been actively deploying GaN and SiC in its semiconductor manufacturing.

The Development of Taiwan's Semiconductor Industry:

The existing silicon-based semiconductor ecosystem has given Taiwan's semiconductor industry a good foundation. The industry has integrated major domestic and foreign manufacturers, government entities, academia, and research communities to jointly build a solid transnational and cross-domain collaboration platform. Building a complete supply chain for semiconductor manufacturing has helped Taiwan expand into a global semiconductor ecosystem. However, for Taiwan to maintain its dominance in semiconductor manufacturing, it has been essential to develop wide-bandgap semiconductors. This will ensure that Taiwan can continue to leverage its advantages in the semiconductor industry to increase its competitiveness and make contributions to global technology and economic development.

Compound semiconductors have been listed as key national development projects all over the world, and Taiwan's niche advantages include not only the government launched "compound semiconductor program", but also the integration of resources from industry, government, and academia to promote talent training programs. For example, universities and colleges are encouraged to increase compound semiconductor scholarships to recruit outstanding talents from all over the world, establish an employment-oriented technical and vocational system, and cultivate low-level technical manpower, etc. to stabilize Taiwan's leading and key position in the global compound semiconductor industry chain. Today's compound semiconductor technology is becoming more and more complex, and how to make up for the insufficiency of the existing supply chain through upstream and downstream cooperation is an important issue. Looking at the supply chain of compound semiconductors in Taiwan, Taiwan has many wafer factories, and the production of silicon carbide substrates, gallium nitride epitaxy, and corresponding production equipment are key areas that can be developed.

• Low on-resistance to reduce conduction losses in the on-state is important for efficient power conversion.
• High-speed switching performance is vital to reduce switching loss.
• Noise energy absorption is important during abnormal operation. When an overvoltage is applied in the off state, the transistor causes a non-destructive breakdown that absorbs the noise energy and converts it to thermal energy to ensure reliability of the device.

The Differences Between Semiconductor Materials GaN and SiC:

• GaN has faster frequency capabilities: Suitable for consumer device charging, hybrid power, and 5G radio frequency communication applications.
• SiC has a higher voltage tolerance capability: Suitable for applications that require higher voltages such as electric vehicles, supercharging stations, vehicles, and energy sources.

The Applications of Semiconductor Materials GaN and SiC:

In the era of the Internet of Things, green energy, and 5G, the energy efficiency of electronic equipment has become more significant, and compound semiconductors such as SiC and GaN are key to improving efficiency. Since voltage tolerance and output power of SiC and GaN are different, they can be chosen for use in different fields. With the advent of the era of 5G and electric vehicles, the demand for high-frequency, high-speed computing and high-speed charging of technology products has increased. The temperature, frequency, and power of silicon and gallium arsenide have reached a limit, and it is difficult to increase the power and speed. Once the operating temperature exceeds 100 degrees Celsius, they are more prone to failure, so cannot be used in more severe environments. In addition, with increased attention to the issue of carbon emissions, the high energy efficiency and low energy consumption of third-generation semiconductors has led to breakthroughs in applications. Third-generation semiconductors can maintain excellent performance, fast switching speeds, and greater stability at high frequencies, while their small size gives rapid heat dissipation.

SiC and GaN have some overlapping voltage levels and frequencies. SiC is mainly aimed at 600V~3.3kV for high voltage applications in the electric vehicle market; while GaN is expected to open new prospects in 100V~600V power electronics. In addition, GaN has a switching frequency of more than 1 MHz, so in addition to its application in the field of power charging, GaN has a greater market opportunity in 5G wireless communication. In practical applications, SiC has better technology maturity, so the market is growing rapidly, and its application in the xEV market has also become increasingly widespread.

SiC is composed of Si and C, which has a strong bonding force and is thermally, chemically, and mechanically stable. Due to the characteristics of low consumption and high power, SiC is suitable for high-voltage and high-current application scenarios, such as electric vehicles and electric vehicle charging. Infrastructure, solar and offshore wind power, and other green power generation equipment.

The strong bonding force and thermal, chemical, and mechanical stability of SiC give it its low energy consumption and high power characteristics, making it suitable for high-voltage and high-current applications such as for electric vehicles, electric vehicle charging, solar and offshore wind power, and other green power generation equipment.

The small size, low heat generation, and high wattage of GaN makes it very suitable for fast charging of consumer electronic products. GaN’s high voltage tolerance allows it to exert the greatest competitive advantage in the fields of automobile, industry, and telecommunications. In addition to consumer electronics, GaN has wide adoption opportunities in the automotive field, such as for 48V hybrid, DC-DC voltage conversion, in-vehicle wireless charging, in-vehicle data center servers, and even lidar's high-power laser drive, etc. In the long run, consumer electronics, and the automotive and other industry applications will be the three main areas of focus for GaN power semiconductors.

Advantages of GaN:

• Lower on-resistance: reduces losses and improves the energy conversion efficiency.
• Faster electron migration rate: increases the frequency of the AC circuit and reduces the number and volume of external components required.
• Higher voltage tolerance capability: higher wattage charging increases charging speed.
• GaN enables higher power, higher power efficiency, smaller device size, and lower system cost.

Technical Requirements for Testing, Etching, and Packaging of Semiconductor Materials GaN and SiC:

Over the past few decades, the packaging of power chips has been pursuing miniaturization, better thermal performance, and better electrical characteristics, and the packaging technology used has become increasingly complex. In the early years, almost all power chips were packaged by wire bonding, but in recent years, power chips using flip-chip packaging have become more and more common. To further achieve a higher degree of integration in a single package, many chip manufacturers have developed packaging technology that integrates active and passive components on the same substrate and launched products that look like chips but are modules.

Because the probability of defects in SiC wafers is high, wafer defect inspection before production is critical. The most critical step is defect inspection before wafer casting. The opposite is true for GaN devices, where the most critical part is the etch process, where damage to the GaN structure would negatively affect device’s reliability. Therefore, for GaN components, the focus is on inspection after the etching process.

The most challenging part of SiC etching is how to speed up the etching and end-point detection. Rapid etching of this material is difficult due to the relatively high hardness of SiC. Also, because the transistors of SiC components will adopt trench structures in the future, it will be relatively challenging to control the etching depth through to the endpoint.

Because the GaN layer is quite sensitive to damage caused by the etching process, the process speed must be slowed down and carried out carefully. At present, manufacturers are able to control the reaction furnace and plasma, thereby reducing etching speeds to avoid damage to the base material as much as possible.