Becoming the 5G RF King is as exciting as FinFET

At the end of the last century, Professor Hu Zhengming was ordered to lead the team to develop alternative processes in order to solve the problem of the "end of life" of traditional CMOS processes. In the end, FinFET and FD-SOI stood out among many competitors. Both have their own strengths and are difficult to distinguish, but under the influence of multiple factors, FinFET eventually became the successor to the mainstream process.

As the process evolves year by year, the debate over which is better, FinFET or FD-SOI, has gradually subsided. Although FD-SOI has not led the development of advanced processes as vigorously as FinFET, it has also taken a path of its own with the SOI family behind it.

The biggest engine: 5G

Calculated based on the market share of SOI substrate wafers, RF-SOI (SOI for radio frequency), which accounts for 60%, is the backbone of the entire family.

RF-SOI devices have the advantages of small size, small parasitic capacitance, fast speed, low power consumption, high integration, and strong radiation resistance. They are particularly suitable for switches and converters with low insertion loss, high linearity, and high speed. Compared with traditional gallium arsenide (GaAs) and silicon on sapphire (SOS) technologies, RF-SOI can provide excellent RF performance and lower cost at the same time. As the mainstream technology for switches and antenna tuners, 90% of these devices are manufactured by RF-SOI.

With the advent of the 5G era, smartphones have higher requirements for RF devices, giving RF-SOI ample room to play. On the one hand, the design trend of smartphones becoming thinner and lighter with a higher screen-to-body ratio continues to develop, leaving less space for built-in RF front-end functional areas; on the other hand, the power amplifiers, filters, switches, LNAs, and antenna tuners required for 5G RF front-end modules have doubled, and many modules must be integrated into a mobile phone. This contradiction makes designers feel very difficult.

With the existence of RF-SOI technology, this problem can be solved. RF-SOI enables switches, PAs, LNAs, phase shifters, variable gain amplifiers (VGAs) to be fully integrated together, and also has control, bias, memory and power combined functions.

High-performance, large-size RF-SOI substrate preparation and RF switch foundry technologies have proven to be able to meet the performance and capacity requirements of 5G Sub-6GHz applications and are beginning to realize their potential in millimeter wave bands and Wi-Fi 6/6E.

Bernard Aspar, chief operating officer and head of global business unit at Soitec, told Jiwei.com that the proportion of RF-SOI devices in 5G smartphones is increasing. For example, in the Sub-6GHz band, the RF-SOI content is 60% higher than that in 4G; in the millimeter wave band, the 120mm2 SOI content increases; at the same time, RF-SOI is more superior in the Wi-Fi 6/6E MU-MIMO RF front-end.

Currently, the world's RF SOI foundries include Tower Jazz, GlobalFoundries, TSMC, UMC, etc. GlobalFoundries has also launched a 45nm RF-SOI process specifically for 5G applications, which utilizes a high-resistance well-enriched SOI substrate. Among domestic wafer foundries, SMIC and Huahong Grace Semiconductor also have the mainstream process foundry capabilities of RF-SOI technology.

5G will usher in a full-scale outbreak in the next 10 years, and vertical, derivative technologies, applications and spectrum will continue to develop. The evolution and development of these technologies will give rise to more demand for optimized substrates. Therefore, not only RF-SOI, but the entire SOI family will benefit from it. For example, FD-SOI is used for SoC analog/RF integration; piezoelectric (POI) optimized substrates are used to produce high-performance surface acoustic wave (SAW) filter components, mainly for 4G and 5G new radio (NR) bands.

According to the forecast of foreign institutions, RF applications will grow rapidly driven by 5G. The SOI market size will exceed US$1 billion (approximately RMB 7 billion) in 2020 and will grow to US$2.2 billion in 2024, with a compound growth rate of 29% from 2019 to 2024.

Edge computing and cars

The emergence of edge computing has changed the way computing devices around the world process and transmit data. The explosive growth of IoT and new applications that require real-time computing capabilities continue to drive the development of edge computing systems.

As edge computing brings computing and data storage closer to the devices that collect data, energy efficiency and reliability become basic requirements for its core chips. As a unique technology that can integrate multiple functions while still providing lower power consumption for mobile device infrastructure, FD-SOI can be seen as tailor-made for edge computing.

"The growth drivers of FD-SOI are mainly 5G, edge computing, and automotive, while its increased adoption also benefits from the fact that more and more technologies require ultra-low power consumption capabilities," said Bernard Aspar.

FD-SOI is able to operate at 0.4V, which reduces power consumption by up to 80% compared to bulk silicon processes. Depending on the voltage used, performance may be improved by 50%.

FD-SOI can also achieve substrate bias and adaptive substrate bias, can have embedded memory built into the chip, and can integrate RF functions. Some manufacturers have begun to use FD-SOI as the best platform for achieving full integration of 5G FEM.

As a mature technology, it started at 65nm and evolved from 28nm and 22nm to 18nm and 12nm. Driven by companies such as GlobalFoundries, ST, and Samsung, products using the 22nm FD-SOI process are now used in fields including IT networks, servers, and consumer electronics. Recently, products related to this technology include the Stellar MCU platform released by ST and the FD-SOI + eMRAM promoted by Samsung Foundry Forum (SAFE).

In the field of automotive electronics, FD-SOI is also making continuous breakthroughs. For example, Dream Chip's industry-first ADAS SoC chip for automotive computer vision applications, Arbe Robotics' 4D imaging radar, and Mobileye's EyeQ4 vision processor all use FD-SOI technology.

Moreover, these are just the tip of the iceberg of FD-SOI applications in the field of automotive chips. As shown in the figure above, most of the main chips used in automobiles are already using this technology.

"In addition, RF managed by AI, bitstream SoC and the next generation of adding radio connectivity to the cloud are also driving a series of innovative applications for FD-SOI," added Bernard Aspar.

Due to the lower R&D cost and excellent characteristics of FD-SOI, the relationship with FinFET has also changed from competition to complementarity. Dr. Dai Weimin, Chairman and President of VeriSilicon, said that the IoT and AI era requires FinFET and FD-SOI. FinFET is responsible for a large number of digital chips and most of the time has high performance, while FD-SOI is suitable for low power consumption and high integration (RF, storage).

The domestic scenery is very good

Recently, Shanghai Silicon Industry announced that it plans to raise no more than 5 billion yuan through a private placement, which will be used for the research and development and advanced manufacturing projects of 300mm high-end silicon wafers for integrated circuit manufacturing, 300mm high-end silicon-based material research and development pilot projects, and to supplement liquidity funds.

The 300mm high-end silicon-based material R&D pilot project mentioned here is to complete the technical R&D of 300mm SOI silicon wafers and conduct intermediate test production.

Under the guidance of 5G, SOI wafer technology has gradually transitioned from 200mm to 300mm. The global suppliers of 300mm SOI silicon wafers are mainly France's Soitec, Japan's Shin-Etsu Chemical and Taiwan's GlobalWafers. There is no 300mm SOI silicon wafer manufacturer with large-scale production capacity in mainland China.

If the project is successfully implemented, the company will establish the production capacity of 300mm SOI silicon wafers and complete the construction of 400,000 pieces/year of production capacity. Shanghai Silicon Industry hopes that the construction of the project will help the company fill the gap in domestic 300mm SOI silicon wafer technology capabilities.

SOI is not a strange topic for the domestic semiconductor industry. In 2015, relevant Chinese companies expressed strong interest in FD-SOI technology. At that time, there was a voice that believed that China should vigorously develop FD-SOI to achieve a technological leap. In the autumn of the same year, Shanghai Simao Technology began mass production of the first batch of 8-inch SOI wafers, using the Smart Cut technology of the company's strategic partner, French company Soitec.

Although SOI did not become a mainstream process, its ecosystem was established in China. Many design companies began to design IoT chips based on the 22nm FD-SOI process, and wafer foundries have also been conducting related research and development. For example, Huali Microelectronics has been developing FD-SOI technology and has delivered products to the market, including 55nm FD-SOI and 22nm FD-SOI.

After entering the AIoT era, SOI has attracted great interest from the Chinese semiconductor industry chain because of its many people-friendly features. However, from the perspective of industry insiders, even though SOI technology has broad development space, its positioning still needs to be clarified. Mo Dakang, a senior semiconductor expert, said, "Any process, such as SOI, has both the advantage of low power consumption and the defect of high cost. The prospects are mainly determined by what products are made. If it is used in products that are sensitive to power consumption, there is hope for the future, otherwise there is no advantage."

Interestingly, the recent chip production capacity shortage has not had a serious impact on the SOI industry chain. An industry insider said that FD-SOI is a new process and only a few companies can make it, so there is rarely a rush for production capacity. This may also be a useful revelation to the industry: develop more differentiated processes and avoid putting all your eggs in one basket, and the probability of production capacity shortages will be greatly reduced.