GaN is being used to transform power applicationsWhile silicon has been the most important material in power electronics for decades, silicon-based devices are now reaching their material’s physical limits.
In response to the ever-growing demand for efficiency, as well as greater power density, the industry is turning to new semiconductor materials to replace silicon. Wide bandgap (WBG) semiconductors, such as gallium nitride (GaN), have many advantages over silicon, enabling lower losses and smaller devices.
In this article, we will look at GaN’s properties, advantages, and how it’s being used to transform power applications.
Material properties of gallium nitride as a semiconductor
GaN features a high electron mobility, which is far greater than that of both silicon and Silicon Carbide (SiC). This physical property, coupled with GaN's ability to withstand higher electric fields due to its wide bandgap, means that GaN devices can operate at higher voltages and temperatures. Consequently, GaN devices can be designed with thinner layers for voltage blocking, allowing them to be smaller than an equivalent silicon-based component without compromising performance. These characteristics make GaN ideal for compact and efficient power electronic devices.
GaN devices can also operate at much higher switching frequencies than silicon and have no reverse recovery losses (an advantage for hard switching discontinuous topologies). As a result, power supplies based on GaN components can achieve higher efficiency than silicon equivalents.
One notable property of GaN is its thermal conductivity, which is lower than its counterpart WBG material, SiC. This impacts how efficiently GaN devices can dissipate heat, meaning that in practice GaN cannot handle as much power as SiC, so GaN devices are typically limited to voltages of about 650 V. But this still covers a huge range of applications, and this limit is steadily being improved in new devices.
Fabrication of GaN substrates
GaN devices are manufactured using epitaxy, where layers of GaN are grown on a substrate. Silicon is frequently used as a substrate because it's readily available and cost-effective. To mitigate the challenges of this, manufacturers employ advanced techniques such as buffer layers that improve lattice matching.
Alternative substrates like sapphire or GaN itself are also used to enhance device performance by reducing lattice mismatch-related defects. The choice of substrate is crucial as it affects the GaN device's electrical properties and overall performance.
Structure of GaN power devices
Figure 1: GaN HEMT structure (cross-section)(Source: Nexperia, https://my.avnet.com/wcm/connect/ece0fcdf-d01f-4e97-aba0-cb3f5ec314eb/nexperia_whitepaper_gan_need_for_efficient_conversion.pdf?MOD=AJPERES&CVID=oRkRsf7)
Operating modes
There are two common types of GaN FETs for power applications, each with different structures and requirements for the gate driver:
- Depletion mode, or d-mode (the GaN transistor is normally on)
- Enhancement mode, or e-mode (the GaN transistor is normally off)
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With the ongoing shift to renewable energy and the electrification of transport and industry, the demand for higher power and greater energy efficiency in electronics is increasing. Wide bandgap technologies including SiC and GaN bring many advantages.
WBG OVERVIEWAdditionally, GaN FETs can be used in a cascode configuration, which is a two-transistor arrangement that can improve performance characteristics such as switching speed and voltage handling.1
Advantages of GaN power devices
GaN devices can typically outperform silicon in efficiency due to their ability to operate at higher switching frequencies with minimal losses and without reverse recovery losses. They also boast a lower on-state resistance (RDS(on)), further reducing conduction losses. These properties not only enhance efficiency but also allow for smaller and lighter devices, contributing to a higher power density in GaN-based applications.
For a more extensive list, see the following article: GaN Semiconductor Advantages.
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Applications of GaN semiconductors in power electronics
With excellent efficiency and high power density, GaN semiconductors can offer significant performance benefits compared to traditional silicon devices. While commonly used in devices up to 650 V, ongoing advancements are expanding their voltage range, and GaN devices are being used across a wide range of power, RF, and optoelectronics applications.
For power, these applications include automotive, where GaN is commonly found in the onboard charger (OBC) and onboard DC/DC converter. In consumer applications, GaN is used in high-power fast chargers for smartphones and other portable devices, providing AC to DC conversion in a compact product.
With the boom in AI, the excellent efficiency of GaN has made it increasingly attractive in power supplies for data centres and servers. Additionally, GaN's high-frequency attributes are being leveraged in telecommunications infrastructure and various industrial applications.
For a more extensive list, see the following article: GaN Semiconductor Applications.
Design considerations
GaN HEMTs are not direct drop-in replacements for silicon MOSFETs and necessitate careful design considerations. One critical aspect is selecting an appropriate gate driver that can accommodate the distinct voltage levels required by GaN devices. Critically, GaN HEMTs operate with lower gate voltages compared than silicon MOSFETs. The gate driver – typically of a bipolar design – must be capable of delivering the necessary current rapidly to support the high-frequency switching of the GaN device. The high frequency of switching also introduces potential issues with noise and electromagnetic interference (EMI), which require careful PCB layout.
Thermal management at a system level must be considered carefully when designing with GaN HEMTs. Their high power density can lead to potential issues that must be addressed.
Challenges in adoption of GaN technology
Historically, the uptake of GaN technology was hindered by its higher cost and the challenges associated with fabrication and achieving significant yields.
However, as the technology has matured, GaN has gained popularity in various power and RF applications. Increased production volumes have contributed to a reduction in costs, making GaN power devices competitively priced in comparison to silicon MOSFETs with similar on-resistance. Furthermore, with advancements in manufacturing methods, the industry's shift towards larger 300 mm wafers from the standard 200 mm is anticipated to further reduce costs.
While its decades-long track record has given silicon a perceived advantage in terms of reliability, GaN has now proven its robustness, with reliability matching that of silicon.
The future for GaN semiconductors in power electronics
According to Yole Group, the market for power GaN devices is expected to grow from US$260 million in 2023 to US$2.5 billion by 2029.2
While GaN has been predominantly used in consumer electronics for power applications, such as fast chargers for smartphones, its usage is set to expand into a number of new applications. The automotive sector is poised for significant growth in GaN adoption, particularly in hybrid and electric vehicles where efficiency and size reduction are critical. GaN is expected to play a vital role in the development of on-board chargers (OBC) and DC-DC converters, which are essential components for managing battery charging and power distribution.
The demand for GaN is also projected to grow in the energy sector, with data centre power supplies seeking to leverage its high efficiency for better energy management and reduced operational costs. As data centres become more central to global infrastructure, the role of GaN in ensuring sustainable and reliable power delivery is likely to become evermore important.
Making the Right Choice
GaN has established itself as a formidable technology for a wide number of power applications, offering proven benefits in terms of efficiency and compactness. If you're considering GaN for your next project, Avnet Silica's team of Field Application Engineers (FAEs) and power engineers are on hand to help you navigate the design intricacies and achieve optimal results in your power system design.
Reference
[1] https://my.avnet.com/wcm/connect/ece0fcdf-d01f-4e97-aba0-cb3f5ec314eb/nexperia_whitepaper_gan_need_for_efficient_conversion.pdf?MOD=AJPERES&CVID=oRkRsf7
[2] https://www.yolegroup.com/strategy-insights/from-power-to-rf-gans-journey-to-a-us4-35b-market-by-2029/
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