What is an AC adapter using GaN (gallium nitride)?

This is a page that explains AC adapters and switching power supplies equipped with GaN (gallium nitride) ICs, which are referred to as next-generation semiconductors. It is used in the USB-PD adapter developed by Unifive.

What Is the Next-Generation Semiconductor, the GaN-Powered AC/DC Power Adapters — Desktop & Wall-Mount?

What Is GaN?

Recently, USB AC/DC Power Adapters — Desktop & Wall-Mount featuring GaN PD have become a common sight in electronics stores. "GaN" stands for Gallium Nitride, a next-generation material that is bringing transformative innovations to the field of power electronics. For decades, silicon-based MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) have played a crucial role in converting energy into power and have become essential in our daily lives. However, improvements in these traditional silicon MOSFETs have reached theoretical limits in terms of power efficiency, and today's technology is approaching a point where further enhancement is no longer feasible.

Moreover, with rising demand for higher power density and efficiency, along with increasing regulations driven by developed nations to curb environmental pollution, silicon is proving difficult to adapt to these environmentally conscious trends. In contrast, Gallium Nitride offers characteristics that meet the growing demands for efficiency, performance, and power density in electrical systems, making it an emerging key technology for next-generation power switching, replacing silicon.

So, What Is Gallium Nitride?

Gallium Nitride does not exist naturally in elemental form. It is typically obtained as a byproduct when refining aluminum from bauxite ore or processing sphalerite to produce zinc, resulting in a significantly lower CO₂ emission during extraction and refinement. Over 300 tons of gallium are produced annually, and global reserves are estimated to exceed one million tons. Since it is obtained as a byproduct, it is relatively inexpensive, costing about $300 per kg, roughly 1/200th the price of gold at $60,000 per kg.

Besides environmental benefits, Gallium Nitride is a binary group III/V direct transition semiconductor, making it suitable for high-power transistors that can operate properly at high temperatures.

History of GaN

Pure gallium has a melting point of just 30°C and can melt in the palm of your hand. It took about 65 more years before Gallium Nitride was first synthesized. Until the 1960s, it was not possible to grow single crystal films of GaN. The compound GaN has a melting point above 1600°C, which is 200°C higher than that of silicon.

In 1972, a GaN-based LED doped with magnesium was developed. This was a groundbreaking event, as it was the first LED capable of emitting bluish-purple light, although it was not yet bright enough for commercial use.

Since the 1990s, GaN has been widely used in light-emitting diodes (LEDs). It emits blue light used in reading Blu-ray Discs and is also applied in semiconductor power devices, RF components, lasers, photonics, and is expected to be used in sensor technologies in the future.

In 2006, production began for enhancement-mode GaN transistors (also known as GaN FETs), in which thin GaN films were grown on AlN layers atop standard silicon wafers using Metal-Organic Chemical Vapor Deposition (MOCVD). The AlN layer acts as a buffer between the substrate and the GaN. This new method allowed GaN transistors to be manufactured using existing silicon fabrication plants and similar processes, enabling low-cost production and reducing barriers to introducing high-performance miniaturized transistors. In more detail, all semiconductor materials have a bandgap, which is the energy range where no electron states can exist, essentially defining how well a solid material can conduct electricity. While silicon has a bandgap of 1.12 eV, GaN's bandgap is 3.4 eV. A wider bandgap like GaN’s means it can withstand higher voltages and temperatures compared to silicon MOSFETs.

This wide bandgap enables GaN to be used in high-power, high-frequency optoelectronic devices. Because GaN operates under far higher temperatures and voltages than Gallium Arsenide (GaAs) transistors, it is also ideal for use in power amplifiers for microwave and terahertz (ThZ) devices used in imaging and sensing applications.

Advantages of GaN

What are the benefits of using GaN—a material that enables high-power, high-frequency optoelectronic devices—in AC/DC Power Adapters — Desktop & Wall-Mount? This section explains the advantages of adopting GaN in AC/DC Power Adapters — Desktop & Wall-Mount.

GaN is commonly compared to silicon-based components. Currently, silicon-based MOSFETs are the industry standard and widely used as power switches in applications ranging from tens to thousands of watts, such as AC/DC and DC/DC power supplies and motor control devices. These have seen continuous improvements in packaging, on-resistance (RDS), voltage ratings, and switching speed.

However, silicon-based semiconductor performance is nearing its theoretical limit due to years of technological advancements, leaving little room for future improvement. On the other hand, gallium nitride-based power devices are high-electron mobility transistors with a higher critical electric field strength than silicon. This high electron mobility means that GaN devices can handle higher electric fields than silicon and, for the same on-resistance and breakdown voltage, offer smaller sizes.

GaN FETs feature very fast switching speeds and excellent reverse recovery characteristics, crucial for low-loss and high-efficiency performance. Currently, many 600/650V rated GaN FETs are already on the market.

The benefits of using GaN in AC/DC Power Adapters — Desktop & Wall-Mount can be broadly categorized into the following three points:

Thermal Advantages

GaN materials have wide bandgaps and offer higher thermal conductivity compared to silicon. This allows devices made with GaN to operate at higher temperatures and be cooled more efficiently, keeping AC adapters cooler and protecting them from heat-related damage.

Smaller Size Through Higher Power Density

Due to higher switching frequency and operating temperature compared to silicon components, GaN enables smaller heat sinks and eliminates the need for cooling fans or reduces magnetic components. Higher switching frequencies also reduce the size of inductors and capacitors used in power circuits, meaning fewer electronic components are needed inside the AC/DC Power Adapters — Desktop & Wall-Mount, allowing for smaller casing.

Reduced Acoustic Noise and Wireless Power Transmission

The higher the frequency, the less acoustic noise is generated in motor-driven applications. Additionally, higher frequencies allow more powerful wireless power transfer, increasing spatial flexibility and widening the air gap between transmitter and receiver. This technology is currently being researched for use in electric vehicle charging systems.

GaN-Powered AC/DC Power Adapters — Desktop & Wall-Mount Developed by UNIFIVE

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