Recently, Huawei Mate60 series phones officially went on sale, which may be seen as a major signal of Huawei’s return to the 5G phone market. In the past two years, although the chips used by Huawei phones integrated 5G baseband, they could only be used as 4G phones due to the lack of 5G RF core devices - bulk acoustic wave (BAW) filters. This situation had a significant impact on Huawei’s phone business. The author will introduce the key technology of 5G RF chips, BAW filters, and analyze the patent status of BAW filters in China and abroad, in order to provide reference for related industries.

Overseas enterprises seize the initiative

The realization of 5G phone communication function depends on 5G chips, which include baseband chips and RF chips. Baseband chips are mainly responsible for signal processing and protocol processing, while RF chips are responsible for RF transceiving, frequency synthesis and power amplification. Although domestic related manufacturers have certain capabilities in independent research and development and production of baseband chips, the localization rate of RF chips is relatively low, and they have long relied on imports. Especially in the field of BAW filters, which are discrete devices, the development difficulty is high, and it has always been the most important part.

At present, the mainstream implementation methods of RF filters are surface acoustic wave (SAW) and bulk acoustic wave (BAW) technologies, both of which use the piezoelectric effect of materials for acoustic device design. Compared with SAW filters, BAW filters show more outstanding performance advantages in high-frequency bands above 2.5GHz, such as large out-of-band attenuation, low insertion loss, low temperature sensitivity and reduced volume with increasing frequency. Therefore, BAW filters have become one of the key technologies for 5G and future 6G communications.

5G communication will further promote the development of industries such as Internet of Things, smart wearable devices, automotive electronics and so on. Due to these industries’ high requirements for communication quality and stability, adopting BAW filters with excellent performance has become a key component of communication systems in these fields. Therefore, BAW filters have a wide range of downstream applications, huge development space and commercial value.

BAW filters need a long time of research and development and technology accumulation to achieve commercialization. Its core technology is mainly controlled by American enterprises, and the main suppliers include Broadcom and Qorvo, which occupy more than 90% of the market share. Their RF front-end chips containing BAW filters are widely used in phones of brands such as Apple, Samsung, Xiaomi, OPPO, vivo and Honor. The continuous innovation of 5G communication will further promote the development of industries such as Internet of Things, smart wearable devices, automotive electronics and so on. Therefore, BAW filters have a wide development space and huge market potential in downstream applications, becoming a key point for major technology enterprises to layout patents.

Globally, patent layout of BAW filters has covered more than 3,000 patent families. From the trend of patent applications, before 2000, there were few patent applications related to BAW. During 2001-2015, the patent application volume remained relatively stable, with an average annual application volume of about 30. During 2004 and 2012-2013, there were two small application peaks, with annual patent application volume exceeding 40. Since 2016, with the rapid development of 5G technology, the importance of BAW filters gradually emerged, and the patent application volume showed a surge trend, increasing from more than 100 per year to more than 300 per year, indicating the high enthusiasm for research and development in this field.

According to the statistics of global patent application volume in the field of BAW filters, Samsung Electronics Co., Ltd., Broadcom Corporation and North (Tianjin) Microsystem Co., Ltd. (hereinafter referred to as North Company) ranked among the top three applicants. Although Samsung Electronics Co., Ltd. and North Company have a large number of patents reserves, their patent layout started relatively late, and they have not yet carried out large-scale production of BAW filters. Broadcom’s BAW business mainly originated from Avago Technologies, which completed the merger in 2015, while Avago Technologies’ related patent layout began in 1996, and basically completed its patent layout before 2015, building a high patent barrier. As of now, Broadcom’s patent applications related to BAW filters have exceeded 200, mainly FBAR (film bulk acoustic resonator), and its patented technology mainly involves the structure and manufacturing method of filters.

In addition, Qorvo Inc., Qualcomm Inc. and Resonant Inc. also play an important role in this field, and their related patent applications have exceeded 100. In 2022, Murata Manufacturing Co., Ltd. of Japan acquired a RF filter startup company, mainly because of the latter’s invention of a new type of bulk acoustic wave filter technology - XBAR filter. Compared with traditional BAW filters, this filter has a simple manufacturing process, which can greatly reduce costs.

Domestic manufacturers actively layout

At present, the domestic self-sufficiency rate of filters is low, and phone filters mainly rely on imports, resulting in a large supply gap and a broad market space. Although foreign enterprises have core technologies and patents, which pose certain entry barriers for domestic manufacturers, China attaches great importance to the independent and controllable technology in this field, actively promotes the cooperation of industry, university and research, and the localization substitution of filters has become an inevitable trend.

There are currently more than 2,000 patent applications related to BAW filters in China, of which more than 60% of the applicants are domestic applicants. Similar to the development trend of global patent application volume, since 2018, the patent application volume in this field in China has also entered a period of rapid development. Among the top ten applicants, there are three foreign applicants, Samsung Electronics Co., Ltd., Broadcom Corporation and Qualcomm Inc., while the important domestic applicants include North Company, Suzhou Hantianxia, University of Electronic Science and Technology of China, Shenzhen New Voice Semiconductor Co., Ltd., Hangzhou Zuo Lan Microelectronics Co., Ltd., Wuhan Minsound and CETC No.13 Research Institute.

It should be pointed out that North Company and Tianjin University have cooperated deeply in the field of BAW filters, and jointly applied for more than 200 patents since 2012. These patents cover many important aspects such as filter and duplexer design, manufacturing and packaging. It is worth noting that Wuhan Minsound, as an emerging enterprise, started to layout related patents since 2021. Its patent content mainly involves key technologies such as filter structure, manufacturing and packaging, and has made major breakthroughs in industrialization. Wuhan Minsound cooperated with SAWTRON Electronics Co., Ltd. to jointly build a large-scale production line of 8-inch BAW RF filters in Beijing, and announced the mass production of BAW filters on July 16, 2023. These innovations and breakthroughs demonstrate these enterprises’ research and development strength and market competitiveness in the field of filters.

Generally speaking, Chinese enterprises have rapidly emerged in the field of BAW filters in recent years, occupying a leading position in domestic application volume. However, the current market is still dominated by foreign enterprises, because these foreign enterprises have earlier and successfully laid out patents, forming a certain patent advantage. Therefore, how to avoid the patents of foreign enterprises, develop mass production technology with independent intellectual property rights to support the development of 5G and next-generation mobile communication is an urgent problem to be solved.

In view of this problem, the author suggests that domestic manufacturers should not only track and study the technology development route of foreign enterprises, in order to catch up with the traditional BAW filter technology, but also consider using new XBAR filters as a breakthrough point. At present, the patent application volume in this field is relatively small, and domestic manufacturers can concentrate their efforts to overcome this new technology and achieve overtaking on curves. We have reason to believe that with the joint efforts of relevant enterprises in the industrial chain, China’s domestic 5G RF filters will break through the encirclement and achieve industrial upgrading and prosperous development.