Media Coverage | The Rise of UHV GaN: Can Silicon Carbide Survive?

The article is reprinted from "Electronic Engineering Album", Zhao Mingcan, November 7

In recent years, gallium nitride (GaN) has rapidly emerged as an attractive wide bandgap (WBG) semiconductor material in medium and low voltage applications. This material has shown great potential in portable electronic devices due to its high performance and small size. However, the technological progress of gallium nitride does not stop there, and its potential in high voltage applications is equally impressive.

Recently, at the 2024 CEO Summit held concurrently with the International Integrated Circuit Exhibition and Conference (IIC Shenzhen 2024), Doug Bailey, Vice President of Marketing at Power Integrations (PI), delivered a controversial speech titled “Will SiC Survive the Emergence of Super-High Voltage GaN?”, discussing the rise of ultra-high voltage gallium nitride technology and its potential impact on the silicon carbide (SiC) market. This speech is not only thought-provoking, but also has important practical significance.

Bailey pointed out that Power Integrations recently launched a 1700V GaN device, which is the first GaN device to exceed 1250V. The company had previously launched a 1250V device a year ago. These developments show that GaN technology is rapidly advancing and gradually approaching or even surpassing the performance of SiC. Bailey emphasized that this series of innovations is aimed at replacing SiC, which is the company's mission.

According to the Net Zero Economy Investment Map released by the International Energy Agency (IEA), about $4 trillion is invested each year in equipment, systems and machines that require power semiconductors. This is a huge market covering hydrogen energy, power systems, transportation and industrial process electrification, as well as renewable energy such as solar and wind power. Wide bandgap semiconductors such as gallium nitride and silicon carbide have broad application prospects in these fields.

Why are wide-bandgap semiconductors like gallium nitride and silicon carbide more popular? Fundamentally, these materials dissipate less energy and are more efficient. High efficiency means that the same functionality can be achieved in a smaller space. In addition, these materials can still do the job when other materials cannot meet the needs. High efficiency also saves costs when processing energy. However, despite the fact that silicon performs poorly in many aspects, such as high energy dissipation, large size, and poor dynamic performance, it is still widely used, mainly due to its long history.

As a high-voltage power semiconductor, silicon carbide is superior in almost every imaginable way. Whether in terms of efficiency, mechanical size or electrical applicability, gallium nitride is comparable to silicon carbide, but in terms of voltage width, gallium nitride is just getting started. "This is exactly what we have been working on in power integration." Bailey said.

Cost is one of the most important considerations for semiconductor switches. Where does the cost come from? First of all, it is the material cost. Silicon, carbon and nitrogen are not rare elements. The rarest element is gallium. However, there are actually a lot of gallium resources in the world. If mining is not restricted, the cost can be greatly reduced.

Next is the yield issue. GaN lags behind SiC in yield and lags far behind silicon. This is also an important aspect that Power Integrations is working on to improve the product cost structure.

Bailey further pointed out two insurmountable defects of silicon carbide, which gallium nitride was able to overcome. The production of silicon carbide requires a lot of machines and time, epitaxial growth is very slow, and the furnace needs to work for a long time, resulting in high machine costs. In addition, silicon carbide needs to be processed at extremely high temperatures, while gallium nitride can be manufactured using ordinary CMOS processes. "In my opinion, these two 'defects' of silicon carbide are fundamental problems of the material itself and are difficult to overcome."

Why are wide bandgap materials better than silicon? As the grain size increases, the total loss (conduction loss + switching loss) decreases. Studies have shown that wide bandgap semiconductors exhibit excellent conductivity when turned on.

"Superconductors have a very thin film or charge carriers that experience very little resistance as they move through the material. As a result, these devices or materials have significant advantages in terms of conduction losses," Bailey explained.

Another key parameter of a power switch is the switching frequency at which it can operate. Wide bandgap materials have very low switching losses when switching power frequently in the kilohertz, 10,000 hertz, or even megahertz range. Due to their smaller physical size, they do not need to discharge a large output capacitor when switching, so switching losses are significantly reduced.

Combining these two points, the overall loss reduction means that wide bandgap materials have an unshakable advantage over silicon. For any application, wide bandgap materials are a better choice, the only difference is cost.

Defining power levels in multiples of 10, from 10W (perhaps a 10W mobile phone charger) to 1GW (perhaps energy transmitted via high-voltage DC lines), locates a range of typical applications, including high-voltage applications such as heating, ventilation and air conditioning (HVAC) and wind power generation - wind power generation has reached 10MW or even 20MW levels, high-speed trains and inverter-driven electric vehicles also reach hundreds of MW, to bridges in electric vehicle charging, to laptop adapters and even refrigerator power supplies.

What is the dominant technology in the laptop adapter space? Bailey said: "It is very clear that GaN is the mainstream technology. If you have a new laptop adapter, there is a high probability that it uses GaN technology inside. I would say that GaN is mainstream at the 100W level."

At the 1kW level, such as server power supplies, car chargers, and DC-DC converters, GaN is the winner. At the 10kW level, that is, large server power supplies and solar arrays, GaN also performs well. In Bailey's view, GaN is undoubtedly a better technology than MOSFET or silicon carbide.

He believes that in the field of electric vehicle traction, although people have been trying to use silicon carbide, gallium nitride will eventually achieve this goal.

At very low power levels, when very compact, ultra-small products are needed, GaN is ideal, but for a 10W power supply, GaN devices may be too small to be easily manufactured and assembled, so the advantages are not obvious.

In the high-voltage field, IGBT will still be the preferred device, but the 1MW level may be an exception. This is also the direction of development that Bailey believes silicon carbide will develop, that is, it will hover between IGBT and gallium nitride, but gallium nitride will dominate in 1MW products.

Looking back at the development history of the power supply field, silicon-based devices have been used for a long time.

About four or five years ago, PI launched the first 750V GaN device. "This GaN device we launched has performed very well in the automotive field. GaN is well known and loved in the automotive field and is widely used in automotive emergency power supplies. It works well on a 1200V bus. The automotive industry usually only needs 800V, but they like to have more margin. Therefore, we launched a 1700V device. We have passed automotive certification for 700V, 900V and 1700V. In fact, the 900V GaN device has also passed automotive certification. Therefore, it is an ideal choice for 400V bus applications. You can use GaN devices in automotive applications." Bailey introduced.

Last year, PI introduced a 1200V GaN switch. This switch is particularly suitable for protecting applications that use industrial power supplies, or those areas where the mains power may be unstable. For example, India prefers to use 1250V devices in metering systems.

Just on November 4, PI launched a 1700V GaN device. "We are very proud of this," said Bailey.

“From a market applicability perspective, as voltages go up, we’re going to expand in a very aggressive way. We started with mobile phone chargers, TVs, laptop adapters, and now we’re in car charging, metering systems, solar arrays and battery storage,” Bailey said.

Let's look at the relative efficiency of GaN switches. There are three curves in the figure below. On the left is a 750V GaN switch, which operates at about 400V. Once you exceed 400V, you need to use new 1700V devices. In contrast, silicon's efficiency drops significantly when the voltage increases. GaN has no significant efficiency loss, which means that when designing an application, if you use PI's devices, you can upgrade the switch without affecting efficiency, providing additional protection and voltage margin.

Traditionally, the best alternative to get high voltage support from silicon is StackFET, which is a StackFET in series on a 750V low-voltage gallium nitride. It can be noted that at a voltage of 900V, its efficiency is about 82%, and at a bus voltage of 900VDC, its losses are almost halved. "This is a better way of thinking. When we increase the efficiency from more than 80% to more than 90%, the losses can be reduced by half. Or, you can get twice the energy from the same volume. This is very important." Bailey pointed out.

In addition, not all GaN is the same. When designing its initial GaN products, PI decided to use depletion-mode GaN, while other companies used enhancement-mode. For PI's application areas, depletion-mode GaN is more suitable due to its ruggedness and reliability.

Here is an example of a laptop charger. Typically, laptop chargers have an efficiency of 90% or 89%. "The EU is the most stringent country in the world for laptop charging, with a charging efficiency of 89% for chargers around 60W. Our efficiency is over 95%, which is half the loss of the best and most stringent international standards, and can produce the most compact chargers and adapters in the world," said Bailey.

This actually uses two GaN devices, one is a GaN switch for the main switch, and the other is an active clamp power switch for recycling leakage inductance energy, which is the common active clamp flyback topology. Its purpose is to maximize efficiency, reduce the size of the power supply, and increase power density.

In short, GaN is now widely used around the world. Whether it is in refrigerators, air conditioning systems, servers, or coffee machines, it can be seen. GaN was first used in adapters, but now it is everywhere.

Therefore, Bailey strongly recommends to engineers, "When you are considering future product designs, especially power subsystems, be sure to consider gallium nitride, it is indeed the best choice"!