What the Future Holds for WBG Devices

Silicon carbide (SiC) and gallium nitride (GaN) have seen increasing success in the semiconductor device market in recent years. GaN is now used in chargers and charging systems for mobile devices. Companies such as Apple, Samsung and Xiaomi have chosen GaN-based chargers that offer high power densities while maintaining or even reducing the weight of these components. These chargers use power GaN high-electron-mobility transistor (HEMT) chips offered by companies such as GaN Systems and Navitas Semiconductor.

On the other hand, SiC devices have been mainly used in the field of electric mobility. In 2017, electric vehicle manufacturers such as Tesla chose to use SiC-based motor controllers, increasing the efficiency of their systems. This has started a race to develop high volumes of SiC devices to meet the increasing number of EVs being introduced into the market.

Their popularity begs the question: What is so special about these new semiconductor materials, and why are they being looked at as alternatives to silicon?

SiC and GaN vs silicon

As explained by Victor Veliadis in his July 28, 2022 PSMA webinar, “SiC Power Technology Status and Barriers to Overcome,” “SiC and GaN materials have a critical electric field that is approximately 10× higher than that of silicon, with a band gap it is 3× higher. In a semiconductor system, it is the drive layer that holds its nominal voltage, allowing the thickness and doping levels of this layer to determine the voltage capability of the device.”

For a specific nominal voltage, the thickness of the driving layer is inversely proportional to the critical electric field. This implies that GaN and SiC devices with a specific voltage capability have drive layers that are 10× thinner than those of silicon devices. These factors drive design changes and have major implications in semiconductor design.

Due to their thinner driving layers, SiC devices are smaller in size, which reduces their capacitance. These devices can therefore switch efficiently at frequencies much higher than what is possible with silicon. Due to the higher switching frequency, the size of passive components and magnetic devices such as inductors also decreases. This results in a significant reduction in the overall size of the system, increasing its power density. Furthermore, the large SiC band gap and high thermal conductivity allow for high temperature operation with simplified cooling management, further reducing system weight and volume.

None of this is to say that either SiC or GaN is better or that silicon is obsolete. The choice of semiconductor material to be used will depend on the specifications of the application in which it is deployed. Silicon is still a strong contender in devices rated from 15 V to 650 V, while also being much cheaper and more reliable, while GaN has become popular in low-power applications such as mobile chargers and similar charging systems. As previously mentioned, GaN is the only viable wide-bandgap alternative to silicon in low-power applications, as SiC operation is impractical at voltages below 650 V.

Power factor correction

GaN enables a power factor correction (PFC) technology known as “totem pole bridgeless PFC topology.” On the other hand, a traditional silicon amplification solution will have a diode bridge where two of the diodes are constantly on. This will add significant losses, but is mitigated by GaN due to its essentially zero reverse recovery. 100-V GaN devices are also being deployed in data centers as server racks increasingly move to 48 V. Furthermore, 650-V GaN devices can also be deployed and used for PFC circuits. SiC is suitable for higher power applications than are possible with GaN and is available in voltages ranging from 650 V to 3.3 kV, with higher voltage devices being developed.

Stephen Russell, power device expert at Tech Insights, said during a company webinar: “Gallium nitride has really found its killer app in replacing silicon and USB-C chargers for mobile devices. 2021 [was] a watershed year in market adoption, and we only expect this momentum to continue. However, gallium nitride’s real advantage is its conversion; it is the only viable wide-bandgap substitute for silicon at voltages less than 600 V.”

All of these devices compete heavily against the 650-V capacity, which is important since these devices are used in the 400-V capacity bus for EVs.

EVs

EVs are a critical application for these newly adopted high-bandgap devices as the market is expected to expand. This transformation is taking place as a result of the rapid electrification across sectors and increased awareness about emissions. They can be seen in motor drivers, DC/DC converters, on-board chargers, etc.

SiC is expected to have an edge in the EV sector as more and more manufacturers move to 800-V EV systems, due to its efficient high-voltage operation capability. Transition to higher voltage systems enables higher power output while maintaining the same current levels. This allows copper conductors and other components to be smaller, lighter and cheaper.

Manufacturers such as Porsche, Audi, BYD and Hyundai are already working on 800-V battery systems, while Lucid has a 900-V system in development. As Veliadis said, “Moving to 800 V while keeping the current the same doubles the power, with smaller losses. This reduces heavy copper cables, which brings lighter weight and space-saving benefits.”

Once successfully adopted in the EV space, the demand for SiC devices will further increase manufacturing. This will eventually bring down prices similar to silicon-based devices after mass production. The decrease in cost is an important step, as these devices are more expensive than silicon, with SiC materials costing nearly 2x to 3x as much as silicon.

Price and production

Apart from the high cost, manufacturing SiC has its own set of challenges, such as the presence of defects and slower manufacturing times compared to silicon, and SiC devices are less robust. This discourages people from adopting SiC-based systems and is a challenge to overcome. Due to their high voltage potential, SiC devices are excellent candidates for deployment in power applications such as HVDC transmission and renewable energy systems. For example, in the case of PV applications, although the SiC device cost is 3× higher than that of silicon, the overall system cost is lower due to the reduction in the size of the passive elements.

Market projections for the semiconductor industry

Despite the challenges they face, wide bandgap devices are expected to be widely adopted in many industries and markets. Today, SiC and GaN are the only wide-bandgap semiconductor materials with commercially available power devices for a wide range of applications. Depending on their device power ratings, these materials can find applications in a variety of industries.

There are also projections showing that the SiC market is expected to be worth $6.5 billion by 2027. GaN devices will dominate the low-power mobile application industry, with more devices expected to reach the market with power densities higher than 20 W/ in.³. These devices are expected to bring significant efficiency improvements and provide user convenience.

Unfortunately, SiC substrate and GaN epitaxy on silicon substrate production is more complicated and labor intensive than that of silicon wafers, and this increases costs. Moreover, the SiC and GaN market is much smaller, and it is far from a large-scale standardized division of labor, since the main process technologies are in the hands of a few select businesses. To overcome such issues, SiC and GaN need to be mass-produced, which will bring economies of scale cost reductions.

This article was originally published on EE Times.

Maurizio Di Paolo Emilio has a Ph.D. in Physics and is a Telecommunications Engineer. He worked on several international projects in the field of gravitational wave research by designing a thermal compensation system, x-ray microbeams and space technology for communication and motor control. Since 2007 he has been working with various Italian and English blogs and magazines as a technical writer, specializing in electronics and technology. From 2015 to 2018 he was the editor-in-chief of Firmware and Elettronica Open Source. Maurizio enjoys writing and telling stories about Power Electronics, Wide Bandgap Semiconductors, Automotive, IoT, Digital, Energy and Quantum. Maurizio is currently editor-in-chief of Power Electronics News and EEWeb, and European correspondent of EE Times. He is the host of PowerUP, a podcast about power electronics. He has contributed to a number of technical and scientific articles as well as some Springer books on energy harvesting and data acquisition and control systems.