On October 24, 2023, Infineon announced the completion of the acquisition of GaN Systems, enriching its portfolio of GaN power conversion solutions and leading application technologies. On January 11, 2024, Renesas Electronics and Transphorm, a global supplier of gallium nitride power semiconductors, announced that they have entered into a definitive agreement whereby Renesas will acquire all of the outstanding common shares of Transphorm. Overseas giants have made frequent moves in the GaN market, which will significantly promote the development of GaN technology and changes in the industry landscape, and also fully demonstrate the strategic importance of GaN technology in the field of power electronic devices. In fact, not only in the field of power electronics, gallium nitride is also widely used in optoelectronics, radio frequency and other markets. This article will sort out the information of GaN devices in downstream applications, substrate classification, production costs, technical paths and other dimensions for the reference of industry stakeholders. Firstly, the characteristics of GaN materials are reviewed: high band gap, high saturation electron drift rate, low dielectric constant, and high breakdown field strength, which make it have the advantages of high voltage resistance, small size, high frequency, low loss, low signal transmission delay, and small crosstalk, which also provide a basis for the wide application of GaN.
Source: Public information, and non-network production
Downstream applications
GaN devices are mainly used in optoelectronics, radio frequency, and power electronics. According to the data of the Prospective Industry Research Institute, the downstream applications in the three major fields accounted for 68%, 20% and 10% respectively in 2020. Optoelectronic field: GaN materials can be used to prepare high-performance LED (light-emitting diode) and LD (laser diode) devices, and can also be used to prepare high-performance optoelectronic devices, such as photodetectors, solar cells and optical communication devices. RF: GaN has become a key material for 5G communication due to its high power density, low energy consumption, high frequency and wide bandwidth. At present, the proportion of LDMOS, gallium arsenide and gallium nitride in the field of RF devices is not much different, but with the development of silicon-based gallium nitride technology, the combination of gallium nitride high performance and the cost advantage of silicon-based process makes it a strong competitor for RF power amplifiers in 5G. According to Yole's forecast, by 2025, while the market share of gallium arsenide remains basically unchanged, gallium nitride is expected to replace most of the LDMOS share, accounting for about 50% of the RF device market. Power electronics: GaN power devices have been widely used in the consumer electronics fast charging market, especially in chargers for smartphones and laptops, which make fast charging devices more portable and efficient due to their ability to reduce size while improving efficiency. In addition, with the long-term market cultivation, many gallium nitride manufacturers have begun to release their own high-power products, and have achieved breakthroughs in photovoltaic new energy, data centers, electric vehicles and other applications. It is worth mentioning that there are three main applications of gallium nitride in the field of new energy vehicles: on-board chargers for charging high-voltage batteries, DC/DC converters to convert power from high-voltage batteries to other electronic devices in the car, and traction drive or motor control, which can be used to drive motors. However, compared with the "car" boom of silicon carbide, gallium nitride is still accumulating, and the scale of the automobile market is still small. In addition, GaN can achieve higher power density and efficiency, handle power more efficiently than pure silicon solutions, significantly reduce power losses in power converters, and minimize the need to add cooling devices, enabling smaller and lighter systems to be designed in less space.
Substrate classification
At present, GaN devices mainly use sapphire, SiC, Si and other substrates, but there are lattice mismatch and thermal mismatch problems between the epitaxial layer of GaN and heterogeneous substrates, and the efficiency is reduced. As a substrate, gallium nitride is naturally the most suitable substrate material for the growth of gallium nitride epitaxial wafers, and homogeneous epitaxial growth can fundamentally solve the lattice mismatch and thermal mismatch problems encountered by using heterogeneous substrate materials, and minimize the stress caused by the difference in properties between materials during the growth process. However, because gallium nitride will decompose at high temperatures, it cannot be pulled out by the traditional straight-pull method of monocrystalline silicon production process, and it needs to be synthesized purely by gas reaction, and nitrogen is very stable, gallium is a rare metal, the reaction time is long, the speed is slow, and the by-products produced by the reaction are many, so the production of gallium nitride substrate is demanding on equipment and complex technology, so the production capacity is relatively low, and the market price is high.
Source: Public data collation, and non-network production
GaN-on-sapphire: Sapphire substrate can obtain low cost, large size, high quality single crystal due to mature technology, mainly made into optoelectronic devices, widely used in LED lighting, ultraviolet/blue/green lasers and other optoelectronic fields; With the characteristics of low loss, the device on the substrate can operate at high voltage and high drain current, and the junction temperature increases slowly with the RF power, and the RF performance is better. However, due to the difficulty of growing high-quality, large-size silicon carbide single crystals, SiC is a layered structure that is easy to cleavage and has poor processing performance, which is easy to introduce step-like defects on the surface of the substrate and affect the quality of the epitaxial layer. The price of silicon carbide substrates of the same size is dozens of times that of sapphire substrates, and the high price limits its large-scale application. GaN-on-Si: low substrate cost, fast growth rate, GaN-on-Si is a silicon-based process, with good compatibility with CMOS process, can well integrate GaN devices and CMOS process devices on a chip, can use the existing silicon wafer foundry for large-scale mass production, mainly to produce power devices, RF devices, used in consumer electronics, industrial, data center and electric vehicles and other fields; GaN: It has higher breakdown voltage and electron mobility, which makes GaN an ideal choice for high-efficiency optoelectronic devices and high-frequency electronic devices, but GaN single crystal growth equipment has high requirements, complex processes and high costs, and is currently commercialized in small batches. For applications that pursue optimal performance, such as high-end lasers and certain types of photodetectors, gallium nitride single crystal substrates may be considered.
production costs
The GaN semiconductor industry chain is as follows: substrate → GaN material epitaxy→ device design → device manufacturing. Taking silicon-based GaN devices as an example, according to the data of Julicheng Semiconductor, the die production cost of silicon-based substrate GaN HEMT is mainly composed of substrate cost, epitaxial wafer cost, manufacturing + packaging and testing cost and yield loss cost, accounting for about 7%, 50%, 23% and 20% respectively, and the cost of epitaxial wafer manufacturing accounts for nearly half of the entire die production cost, which is the core process of the entire GaN industry. Compared with silicon carbide, the current manufacturing cost of gallium nitride (GaN-on-Si) and gallium nitride (GaN-on-Sapphire) on silicon substrates is lower than that of SiC-on-SiC, because the cost of substrate materials in the latter is more than 25 times higher, and the wafer manufacturing yield is relatively low. The cost of GaN devices on other substrates is not advantageous. Although silicon carbide is the most cost-effective in the high-voltage field above 1200V, in the high-power scenario of 600V-1200V, the market potential of gallium nitride is huge, and it is becoming its new blue ocean market. It is worth pointing out that the electron mobility of gallium nitride is 2 times higher than that of silicon carbide, so the switching losses of gallium nitride are relatively low. In addition, gallium nitride also operates at a higher frequency than silicon carbide, so the size of the magnetic components used in the circuit can be reduced. The reduced size of the magnetics helps to reduce costs, which is ultimately reflected in the bill of materials (BOM) of the power system.
Technology Path
There are two main technical routes for GaN devices, planar and vertical. Planar GaN devices are typically based on non-intrinsic substrates such as Si, SiC, sapphire, etc. In the early stage, high-quality monocrystalline gallium nitride substrates are difficult to achieve, the cost is relatively high, and heteroepitaxial gallium nitride can only be grown on non-intrinsic substrates. Normally open D-mode (depletion) and normally off E-mode (enhanced) constitute the two main categories of transverse HEMT devices. Because the gallium nitride and AlGaN interface in the device has excellent two-dimensional electron gas (2DEG) to form a natural conductive channel, the devices made without special technology and other technical means are normally open depletion devices. D-mode (depletion) is the natural state of GaN power devices, in the normal state (gate source voltage VGS=0), there is already 2DEG between the drain and the source, the device is in the conduction state, and when the gate source voltage VGS