The battle over GaN routes is rekindled
Latest update time：2021-09-03 04:34
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Gallium nitride (GaN) is rising rapidly due to its excellent performance in high-power and high-frequency working environments. Whether in power or RF applications, GaN represents the future of high-power and high-performance application scenarios and will largely replace gallium arsenide (GaAs) and LDMOS.
In terms of GaN epitaxial wafers, there are two main substrate technologies, namely GaN-on-Si (GaN on silicon) and GaN-on-SiC (GaN on silicon carbide). Of course, in addition to the above two mainstream technologies, there are also GaN-on-sapphire and GaN-on-GaN technologies.
Although GaN-on-SiC has relatively good performance, its price is significantly higher than that of GaN-on-Si. In addition, GaN-on-Si grows faster and is easier to expand to 8-inch wafers. Although GaN-on-Si performance is slightly inferior to GaN-on-SiC, devices manufactured at the current process level can reach 5-8 times the original power density of LDMOS. When operating at a frequency higher than 2GHz, the cost is not much different from that of LDMOS with the same performance. In addition, silicon-based technology will also be compatible with CMOS processes, allowing GaN devices to be integrated with CMOS process devices on a single chip. These have made GaN-on-Si the mainstream of the market, and it is mainly used in the field of power electronics. In the future, it is expected to be introduced in large quantities into the power amplifiers (PA) of 5G base stations.
GaN-on-SiC combines the excellent thermal conductivity of SiC with the high power density and low loss capabilities of GaN. Compared with Si, SiC is a very "dissipative" substrate. Devices on this substrate can operate at high voltage and high drain current, and the junction temperature will slowly increase with the RF power, so the RF performance is better, making it a suitable material for RF applications. Under the same dissipation conditions, SiC devices have better reliability and service life. However, due to the limitations of SiC substrates, it is still limited to 4-inch and 6-inch wafers, and 8-inch wafers have not yet been promoted.
Additionally, SiC has high resistance properties: this is very beneficial for millimeter wave transmission, which is required when designing high-frequency MMICs with large matching circuits.
Figure 1: Development trend of GaN-on-SiC and GaN-on-Si applications (Source: YOLE)
In terms of RF applications, Cree (Wolfspeed) has the strongest strength. In the patent competition for GaN HEMT for RF applications, especially in GaN-on-SiC technology, the company is in a leading position, far ahead of its main competitors Sumitomo Electric and Fujitsu. Intel and MACOM are currently the most active RF GaN patent applicants, mainly focusing on the field of GaN-on-Si technology. New entrants in the field of GaN RF HEMT-related patents are mainly Chinese manufacturers, such as HiWafer, Sanan Integrated Circuit and Huajin Chuangwei.
GaN-on-SiC epitaxial wafers have another breakthrough
Compared with GaN-on-Si, the biggest disadvantage of GaN-on-SiC is its cost. If this problem is solved or the costs of both parties are made close, the performance advantage of GaN-on-SiC will be highlighted.
Europe has been at the forefront of the world in the research of third-generation semiconductor technology, and breakthrough technologies often emerge. Recently, a Swedish company delivered 6-inch wafers with its GaN-on-SiC technology. The company's chief technology officer and co-founder said: "In the current market, 99% of GaN devices are GaN-on-Si because silicon substrates are cheap and can be vertically integrated. However, the quality of GaN-on-Si still has many defects. The biggest problem is reliability. In this regard, GaN-on-SiC does better. We used a different growth scheme to develop this technology. GaN-on-Si must grow 5μm thick to obtain good quality, but its silicon substrate has defects, and the SiC layer is 2μm. Now, we have reduced its thickness to 200 to 250nm, which can improve quality and reduce defects. "
据悉，该公司是与Linköping大学和法国研究小组IEMN合作研究该外延技术的，这也是EU Horizon 2020项目的一部分，使用了具有有序空位的1nm原子中间层来适应第一外延层和衬底之间界面处的晶格失配。这使半绝缘SiC衬底上的300nm GaN层具有约2 MV / cm的横向临界击穿场和超过3 kV的垂直击穿电压。该临界击穿场几乎比传统的厚缓冲法生长的硅上GaN外延晶片的击穿场高三倍。这一突破可以显著降低大功率器件的功耗。
As shown in the figure below, a layer of aluminum nitride (AlN) can be seen under the channel, which has the highest band gap. This barrier helps confine the electrons within the channel, which is another way to reduce the thickness.
figure 2
In practical terms, this thin epitaxial layer shows a higher breakdown strength, four times that of silicon.
Yield is a very important indicator, and currently, the yield of GaN-on-Si is still about 60%, so there is still a problem. With this GaN-on-SiC solution, its substrate is easier to handle than silicon, so the yield will be much higher.
At present, this thin and light GaN-on-SiC solution is mainly used for radio frequency, and will move towards power applications in the future. Because it can achieve higher power, it is more irreplaceable than GaN-on-Si, especially in electric vehicle applications, where the target voltage is generally 900 to 1200V. In this regard, GaN-on-SiC has more advantages, and the cost of the substrate will be reduced. In the past three years, the cost of GaN-on-SiC wafers has been greatly reduced.
GaN-on-SiC is also moving towards 8-inch wafers, as this is the mainstream of wafer foundries, but as of now, 8-inch SiC wafers are not widely used. There is a saying in the industry that 8-inch SiC will become a standard wafer product within two years.
In short, for RF applications, GaN-on-SiC must be thinner and provide better confinement for VHF devices. For power applications, the structure given by the Swedish company is sufficient, but it still needs to work on cost. Bulk orders for RF will help reduce substrate costs.
Chinese manufacturers are also actively developing GaN technology. In recent years, related epitaxial wafer projects have been put into production one after another. For example, in the second half of 2019, the third-generation semiconductor material manufacturing project (Phase I) invested and constructed by Beijing Naiwei Technology Holding's subsidiary Juneng Jingyuan was officially put into production in September. The project has a designed annual production capacity of 10,000 GaN epitaxial wafers, which can produce GaN epitaxial wafers with standard structures, and can also develop and mass-produce customized epitaxial wafers according to customer needs.
At the same time, the first GaN epitaxial wafer factory in the western region, Julicheng, successfully trial-produced GaN epitaxial wafers. In the field of power electronics, Julicheng has the technical capabilities to develop 6-inch 650V/100V silicon-based gallium nitride (GaN-on-Si) epitaxial wafers and realize the production process of 650V/15A silicon-based gallium nitride power devices. In the field of microwave radio frequency, the company also has the technical capabilities to develop GaN-on-SiC epitaxial materials, and its products are mainly positioned in the radio frequency communication and radio frequency energy markets.
At present, many domestic companies have laid out the GaN epitaxial wafer industry. In addition to Julicheng, there are Jiangsu Nenghua, Innoscience, Sanan Integrated, Jiangsu Huagong, Dalian Xinguan and Hiwin Huaxin. Among them, Innoscience's 8-inch Si-based GaN production line has been put into use one after another.
Fab
At present, many wafer foundries and IDMs are involved in the production of GaN-on-Si and GaN-on-SiC, and both are their key development targets.
In terms of wafer foundry, enterprises in Taiwan are leading the way. In terms of GaN-on-S, TSMC has begun to provide 6-inch wafer foundry services. Chipstar's 6-inch GaN-on-Si epitaxial wafers have entered the international IDM factory certification stage and are striving for new orders. Hanlei Technology has already mass-produced 6-inch GaN on Si products, targeting automotive demand.
Compound semiconductor wafer foundry WIN Semiconductors has begun to provide 6-inch GaN-on-SiC foundry services, targeting high-power PA and antenna applications; while Huanyu also has 4-inch GaN-on-SiC high-power PA production capacity, and its 6-inch GaN-on-SiC wafer foundry capacity has been certified.
World Advanced has also invested in GaN materials for more than four years, and has continued to work with equipment material manufacturer Kyma and its indirect investment in GaN silicon substrate manufacturer Qromis to develop a new substrate high-power gallium nitride technology GaN-on-QST that can reach 8 inches. A small number of samples are expected to be sent this year, and the initial stage will mainly target power supply applications.
Last week, Sino-American Crystal announced that it had acquired a stake in Macronix, and the two parties will work together to accelerate the development of GaN products. Macronix has independent technology in the field of GaAs wafer foundry, and has also actively developed GaN products in recent years, and the transition from GaAs to GaN-on-SiC process is relatively fast.
In terms of IDM, there are currently about 20 manufacturers at home and abroad that design and produce GaN, especially base station RF devices. This is not a large number. Representative ones include Qorvo, Infineon, NXP, Cree, Sumitomo of Japan, ADI, MACOM, as well as Sanan Optoelectronics, Hitech High-tech (Haiwei Huaxin), Suzhou Enxun and Innoscience in mainland my country.
Among them, Cree mainly operates the RF business through its subsidiary Wolfspeed. In 2018, Cree acquired Infineon's RF department, which mainly designs and manufactures LDMOS amplifiers and has the production capacity of GaN-SiC/Si devices. After the acquisition, Cree became the world's largest supplier of GaN RF devices. In addition to producing GaN RF devices for itself, Cree also provides GaN foundry production services to the outside world.
Qorvo has further developed GaN-on-SiC based on GaAs; MACOM was optimistic about the GaN-ON-Si process in the early stage and has also started to develop GaN-on-SiC in the past two years. For example, last week, it released its new GaN-on-SiC power amplifier product line, called MACOM PURE CARBIDE. The company also launched the first two new products of this product line, MAPC-A1000 and MAPC-A1100.
Conclusion
The above mainly introduces the advantages and disadvantages of GaN-on-Si and GaN-on-SiC technologies, as well as their respective development trends, and analyzes the current development status of manufacturers in this field from the aspects of epitaxial wafers, wafer foundry and IDM.
Compared with a few years ago, more and more manufacturers pay attention to GaN-on-SiC and invest in R&D, and the corresponding products are increasing. With the gradual resolution of cost and other issues, the performance and other advantages of GaN-on-SiC are expected to stand out in the future, especially in the field of RF applications, where GaN-on-SiC has better development prospects than GaN-on-Si.
*Disclaimer: This article is originally written by the author. The content of the article is the author's personal opinion. Semiconductor Industry Observer reprints it only to convey a different point of view. It does not mean that Semiconductor Industry Observer agrees or supports this point of view. If you have any objections, please contact Semiconductor Industry Observer.
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