Knowledge Popularization: What is gallium nitride

2024-01-30 660

If you are familiar with the fast charge industry, then "gallium nitride" must be very famous on the list. I believe that most readers have heard of this "noun". It frequently appears in the publicity media of various charging products, industry summit reports and industry media articles.

So what exactly is gallium nitride?

Understanding gallium nitride

Gallium nitride (GaN, Gallium nitride) is a compound of nitrogen and gallium and is a direct bandgap semiconductor of groups III and V.

The structure is similar to wurtzite and the hardness is very high. Gallium nitride has a wide energy gap of 3.4 electron volts and can be used in high-power, high-speed optoelectronic devices.

Material property

Gallium nitride (GaN) is a kind of wide-gap direct bandgap semiconductor, which has a wide direct bandgap, high breakdown field strength, high thermal conductivity and very good physical and chemical stability. In addition, like other nitrides of Group III elements, gallium nitride is less sensitive to ionizing radiation and has higher stability.

The physical appearance is generally yellow powder, like lead-zinc mineral crystals, with a molar mass of 83.73 g/mol g·mol⁻¹, a melting point above 2500°C, and a density of 6.15 g/cm3. It can produce chemical reactions in contact with water and is non-flammable.

Research and development background

Gallium nitride was first synthesized in 1928, and through technological improvements over the next 70 years, it became widely used in light-emitting diodes in the 1990s, initially developed to make light-emitting diodes in colors ranging from red to ultraviolet.

Later in the application process to replace silicon based devices on semiconductors, we have introduced the material characteristics of gallium nitride (GaN), which can be found that its characteristics are significantly superior to silicon based devices. Gallium nitride crystals can be grown on a variety of substrates, including sapphire, silicon carbide (SiC), and silicon (Si). Growing GaN epitaxial layers on silicon can use existing silicon manufacturing infrastructure, eliminating the need for costly specific production facilities and using low-cost, large-diameter silicon wafers.

Scope of application

Gallium nitride has a wide range of applications, and is widely used in military electronics, communications, power devices, integrated circuits, optoelectronics and other fields. The following is a brief introduction to the application range of gallium nitride.

Charging product

As a self-media focused on the field of charging, we mainly talk about the application of gallium nitride in charging products, and the history of gallium nitride widely used in charging equipment is not long.

The gallium nitride charging chip was introduced to the market in 2014, shortly after the establishment of Nano Technology, launched the world's first gallium nitride power IC prototype demo. It was adopted by manufacturers and applied to charging equipment in 2018, and was first adopted by the domestic ANKER PowerPort Atom PD1 charger.

After the introduction of gallium nitride chargers, with its excellent power density and charging performance was soon favored by consumers and manufacturers, and subsequently, more and more manufacturers began to replace silicon-based equipment with gallium nitride materials to produce chargers. By now, gallium nitride chargers have almost become synonymous with high-performance chargers.

So what is the magic of gallium nitride, the third-generation semiconductor material, that can improve the charging performance of the charger while greatly reducing the overall size? To answer this question, first we need to understand how the charger works.

Working principle of charger

We take 100W gallium nitride a brand of mobile phone charger as an example, according to its working principle to look at the role of gallium nitride, the red frame surrounded by the component is gallium nitride material.

First of all, 220V AC passes through the fuse, EMI filter circuit, rectifier bridge to turn it into high voltage direct current, and then the current will pass through a series of filter circuit, PFC boost circuit (PFC controller, PFC switch tube, PFC boost inductor), into the PFC rectifier tube, and then enter the high voltage filter electrolytic capacitor, filter out the clutter, Enter the switching power supply circuit.

Switching power supply circuit, the main control chip controls the primary switching tube to switch at a certain frequency through the feedback information of the protocol chip, and the transformer outputs the low-voltage alternating current that meets the requirements. The synchronous rectifier controller controls the synchronous rectifier tube to rectify the low-voltage alternating current into low-voltage direct current, and the solid-state capacitor filters out the clutter.

Finally, the current passes through the corresponding protocol chip and outputs stable low-voltage direct current in line with the protocol specifications into the charging device. Even if the entire charging process is completed, the process of charging the mobile phone is also the process of transforming high-voltage alternating current to low-voltage direct current.

So what exactly is the role of gallium nitride in this workflow?

The role of gallium nitride switching tubes

Through the flow chart, we know that gallium nitride materials mainly exist in the PFC switch tube and the primary switch tube in the charger, so to understand the role of gallium nitride first understand what the switch tube is doing? And what does the switching tube of gallium nitride do?

Answer the first question first -- what does a switch tube do?

As the name suggests, the switch tube is equivalent to a switch, which is used to control the flow of electrons, and the input high level can let the electrons flow freely, and the low level current is stationary. Switching on and off during this process can turn the current into a high frequency pulsating current. Why does it become a high frequency pulsating current?

A knowledge point involved here is that the frequency f of the pulsating current is directly related to the volume of the transformer, according to Faraday's law of electromagnetic induction, it can be expressed by such a formula (U=2π*f*N*Bm*S/√2), and the corresponding relationship between the symbols is like this.

Among them, the cross-sectional area of the iron core S and the number of turns per volt N can determine the volume of the transformer, which directly affects the size of the charger. In the real application scenario, taking into account the circuit loss, heat and other factors, N and S can not be reduced at will. If it must be reduced, the more effective way is to increase the AC frequency f.

In the case of constant voltage, the most significant way is to increase the AC frequency f, and the role of the switching tube is to control the AC frequency f.

So then we can answer the second question, what does the gallium nitride switch tube do? Gallium nitride switching tubes have much better performance than previous silicon-based switching tubes, mainly reflected in the following four aspects:

1, higher breakdown strength

2, faster switching frequency

3, lower on-resistance

4, higher thermal conductivity

5, lower switching loss

We have compared the switching tube characteristics of gallium nitride and silicon materials, and can draw the following conclusions:

1) The band gap width of gallium nitride 3.42/eV means that the breakdown electric field strength is higher than that of silicon (11 times that of silicon), and can withstand nearly 3.3 million V voltage without destroying the chemical structure;

2) Higher electron mobility means that the current passing rate is higher, the on-resistance is smaller, and the switching frequency f is higher, thus greatly reducing the volume of transformers and other resistance and capacitance parts.

3) The thermal conductivity of gallium nitride is also higher than that of silicon, which reflects better heat dissipation and less loss of components.

So how does gallium nitride switch loss?

The advantages of gallium nitride in hard switching, in the material itself and the device has advantages, one is the Qg(mainly the Miller capacitance is relatively small, can reduce the switching crossover loss; Second, Coss is low, which can reduce the charge and discharge loss of junction capacitor.

The advantages of gallium nitride in hard switches are that it has a low Coss, which can reduce the dead time and improve efficiency; Second, it has a low Qrr, which can reduce the directional recovery loss.

The above is the superior embodiment of gallium nitride as a switching tube, in a nutshell. The material gallium nitride is mainly used as a switch tube in the charger original, and the switch tube of gallium nitride can significantly reduce the volume of other components of the charger device due to higher breakdown strength, faster switching frequency, lower on-resistance, switching loss and higher thermal conductivity, and make the performance of the switch tube better.

From the overall point of view of the charging product, the benefits of gallium nitride include size, weight and cost reduction, but also include BOM costs (the price of other system components such as capacitors, radiators and inductors), consumption costs and cooling costs. In addition, gallium nitride replacement silicon devices can achieve higher efficiency, higher power density, and possibly both. So gallium nitride will become a popular material for chargers now.

Other applications

In addition to its application in charging products, gallium nitride is also widely used in other fields, according to statistics in May 2022, two-thirds of GaN devices are used in military electronics, such as military communications, electronics, jamming, radar and other fields; In the civil field, gallium nitride is mainly used in communication base stations, power devices, optoelectronics and other fields.

In the field of military electronics, the typical application is active electronically scanned array radar. The image below shows an active electronically scanned array radar with gallium nitride.

At present, the E-2D carrier-based early warning aircraft of the United States is loaded with active electronically scanned array radar with gallium nitride material application, in addition to the early warning aircraft, fighter radar also takes gallium nitride technology as an important direction of future development. On June 28, 2021, the US "Aviation Week" website reported that: at present, the application of gallium nitride (GaN) technology in fighter radar is ready to start. Gallium nitride, already the current semiconductor of choice for 5G electronics and large search radars, is on the cusp of a transition to fighter fire control radar applications, which is expected to enable the largest one-time energy leap for fighter fire control radars since the adoption of active phased array technology in the late 1990s.

In the civil field, gallium nitride is mainly used in communication base stations, power devices and other fields. The power amplifier efficiency of gallium nitride base station PA is higher than that of other materials, so it can save a lot of power, and it can cover almost all the frequency bands of wireless communication, and the power density is large, which can reduce the size and quality of the base station.

In the field of optoelectronics, gallium nitride can be used to manufacture light-emitting diodes and lasers due to its material properties, and purple laser diodes based on gallium nitride are used to read Blu-ray discs. Mixing gallium nitride with indium (InGaN) or aluminum (AlGaN), with a band gap depending on the ratio of indium or aluminum to gallium nitride, can create light-emitting diodes in colors ranging from red to ultraviolet.

Sum up

According to the Research report, gallium nitride can be widely used in communications, computers, consumer electronics, automotive electronics, aerospace and other higher power and higher frequency fields; "Due to rapid commercialization, we will lead the third-generation semiconductor market." Research institute Yole predicts that by 2027, the power GaN device market size is expected to reach $2 billion.

As a third-generation semiconductor material, gallium nitride has not been famous for a long time, and the application field is far from the boundary. At present, the technology development and application expansion based on gallium nitride materials is in the ascendant stage, it can be predicted that in the future, gallium nitride will enter more fields and be known to us.

Every invention and application of new materials is an impact on the industry, which contains both challenges and opportunities. Grasping the application of new materials has great development significance for manufacturers, industries, and even countries. The development and current situation of gallium nitride vividly illustrates this point - now, the track belonging to gallium nitride has opened, and the road ahead is still long, let's wait and see!