Nowadays, the 5G era has developed for a long time. 5G communication has long been a hot topic of great concern to people. In the past, people's focus on mobile phones was usually on CPUs, GPUs, basebands, screens, and cameras. In recent years, with the rapid development and popularization of 5G technology and the strong rise of domestic RF chips, 5G RF chips have gradually come into the public eye.

RF chips are chips that can convert RF signals into digital signals and vice versa. Specifically, they include RF transceivers, power amplifiers (PA), low-noise amplifiers (LNA), filters, RF switches, antenna tuning switches (Tuner), etc.

Among them, filters can be considered the core component of the RF front-end and the key to manufacturing 5G RF chips.

01

Two Mainstream RF Filters

RF filters are important components used in electronic communication systems. Their role is to filter out unwanted signals within a specific frequency range, ensuring the normal operation of the system.

The role of RF filters is mainly reflected in signal processing and system protection. In wireless communication systems, RF filters can be used to filter out interference signals from adjacent frequency bands, thereby improving the system's anti-interference ability and transmission quality. Additionally, RF filters can protect other components in the system, preventing damage caused by unwanted signals. Therefore, RF filters play a crucial role in wireless communication systems.

Therefore, the performance of RF filters is one of the important factors determining communication quality.

RF filters can be classified into acoustic filters, crystal filters, and ceramic filters, with acoustic filters (SAW, BAW) being the mainstream filters currently used in mobile phones.

SAW filters, or Surface Acoustic Wave filters, utilize the propagation characteristics of surface acoustic waves on piezoelectric substrates to achieve signal filtering. When an electrical signal passes through a piezoelectric substrate, it generates surface acoustic waves that propagate at a certain speed on the surface of the substrate. By etching specific patterns on the substrate to form reflectors, the propagation path of the surface acoustic waves can be controlled, thereby achieving selective signal filtering.

The advantages of SAW filters include high selectivity and low insertion loss, low cost and high yield, making them easy to mass produce, as well as mature technology and high reliability. However, SAW filters have some disadvantages, such as temperature sensitivity and high manufacturing precision requirements, especially at high frequencies.

SAW filters are widely used in the front-end of RF communication systems, such as mobile communications, satellite communications, and radar.

BAW filters, or Bulk Acoustic Wave filters, operate on a similar principle as SAW filters, but with the difference that the acoustic waves propagate vertically in BAW filters, allowing for more efficient acoustic wave capture.

The advantages of BAW filters include higher frequency stability, unaffected by temperature changes, a wider operating temperature range, and the ability to achieve higher Q values (quality factors), meaning better selectivity and lower insertion loss. However, BAW filters have higher manufacturing costs, complex manufacturing processes, and relatively low production volumes. According to estimates by Hua'an Securities, the cost of BAW filters is approximately 2-10 times that of SAW filters.

BAW filters are commonly used in applications requiring high frequency stability and temperature stability, such as high-end RF communication equipment, satellite communication systems, and precision measurement instruments.

The choice between SAW and BAW filters primarily depends on specific application requirements, such as the required operating frequency, environmental conditions (temperature stability), and cost budget. For most general communication applications, SAW filters may be a cost-effective choice, while BAW filters may be more suitable for special applications requiring higher frequency stability and a wider temperature range.

02

Specific Applications of RF Filters

Wireless Communication Field

Smartphones are one of the most widely used applications for RF filters, with each smartphone requiring a large number of RF filters to ensure communication quality. For example, in 4G phones, RF filters are used to separate and filter signals across different frequency bands, such as 700MHz, 1800MHz, and 2100MHz, to ensure accurate reception and transmission of signals within the corresponding frequency bands, avoiding interference between different bands. In 5G phones, due to the support of more frequency bands and higher frequencies, the requirements for RF filter performance and quantity are further increased, with typically 70-100 RF filter chips required per 5G phone.

RF filters are also widely used in base stations. At the transmitting end of a base station, RF filters are used to filter out unwanted frequency components from the transmitted signal, ensuring that the transmitted signal complies with communication standards and spectrum regulations. At the receiving end, RF filters are used to screen incoming signals, improving the signal-to-noise ratio and facilitating accurate demodulation of useful information. For instance, in dense urban base station networks, RF filters can effectively filter out interference signals from other base stations, enhancing communication stability and reliability.

In satellite communications, as signal transmission distances increase, numerous spurious signals become mixed into the signal. RF filters can selectively filter out these spurious signals, improving signal transmission quality. For example, in satellite television broadcasting systems, RF filters can screen out specific satellite television signals from complex space signals and transmit them to users' satellite television receivers.

Radar Systems Field

In radar systems, RF filters are primarily used to filter out spurious signals from echoes, improving the radar's signal-to-noise ratio and enabling more precise target detection.

For example, meteorological radars detect meteorological targets in the atmosphere, such as clouds and precipitation, by emitting and receiving electromagnetic waves. Air defense radars need to quickly and accurately detect and track aerial targets. Automotive radars are used to detect obstacles and other vehicles around a vehicle, providing information on their positions and speeds.

RF filters in radar systems typically exhibit high frequency selectivity and stability to ensure the overall performance of the radar system.

Scientific Research and Medical Fields

RF filters also play an important role in scientific research and medical fields.

In medical equipment, RF filters are used to filter out interference signals from bioelectric signals, improving the accuracy and reliability of medical equipment. For instance, in electrocardiographs and electroencephalographs, RF filters ensure that the collected bioelectric signals are purer, thereby enhancing diagnostic accuracy. In scientific research, RF filters can be used in signal processing and spectrum analysis experiments, helping researchers obtain and analyze experimental data more accurately.

03

International Competitive Landscape and Major Manufacturers

The global RF filter market exhibits an oligopolistic competitive landscape, primarily dominated by American and Japanese companies. In the SAW filter market, companies such as Murata, TDK, and Taiyo Yuden hold dominant positions, while in the BAW filter market, Broadcom and Qorvo occupy the majority of market share.

According to Yole data, the global cellular communication filter market reached a size of USD 8.85 billion in 2023. SAW filters still account for the largest share, with a 61% market share and a market size of USD 5.4 billion. BAW filters account for 34% of the market, with a market size of USD 3 billion. By 2027, the overall filter market size is expected to exceed USD 10 billion.

However, due to the relatively weak overall strength of Chinese RF filter manufacturers, their production volumes cannot meet domestic demand, and they have long relied on imports, making it difficult for them to reap the benefits of this vast market.

So, how difficult is it to develop RF filters? And where are domestic manufacturers stuck?

The development of the domestic filter industry does not solely depend on technology itself but also requires a collaborative mode of the industrial chain.

The difficulties in localizing SAW and BAW RF devices lie in their complex manufacturing processes, high-precision material science requirements, reliance on high-end equipment and high-purity materials, technical barriers, and intellectual property protection issues.

For example, in terms of manufacturing process complexity, the production of SAW and BAW devices involves high-precision photolithography to form fine electrode patterns on the surface of piezoelectric materials. In thin-film deposition, uniform and high-quality thin films need to be deposited on piezoelectric materials to ensure stable acoustic wave transmission and device performance. The selection of high-quality piezoelectric materials (such as aluminum gallium aluminum and lithium niobate) is crucial for manufacturing SAW and BAW devices. These materials require strict control of their purity and crystal structure during preparation. The quality of thin-film deposition directly affects device performance and stability, requiring extremely high uniformity and low defect density.

From the perspective of material preparation difficulty, high-performance piezoelectric materials require rigorous process control during preparation, including high-temperature treatment and precise doping control. In terms of supply chain and technical barriers, manufacturing SAW and BAW devices requires advanced lithography machines, thin-film deposition equipment, and high-precision testing equipment, which are typically imported. High-performance piezoelectric materials and other key materials are mostly imported from abroad, and domestic production capacity and technical accumulation are insufficient.

To localize these RF devices, long-term and sustained investments and developments are required in material research and development, equipment manufacturing, and technical accumulation.

Since localizing RF filters is so difficult, should domestic manufacturers still enter this fierce competition? The answer is: Absolutely, they should compete.

Firstly, from a market size perspective, according to relevant data, China's RF filter market has continued to grow from 2020 to 2023, primarily due to the expansion of base station construction and the increasing penetration rate of the smartphone market. It is projected that over the next five years, driven by 5G, China's RF filter market size will further increase and is expected to reach RMB 72.21 billion by 2028.

Secondly, from a communication security perspective, localizing RF filters is of great significance. In terms of communication security, domestic RF filters can reduce dependence on foreign products, avoid potential information security risks, and ensure the secure transmission and storage of domestic communication network information.

From a cost-benefit perspective, localization can reduce production and procurement costs, freeing domestic enterprises from price constraints imposed by foreign suppliers. By procuring RF filters domestically, enterprises can shorten supply chains, reduce transportation costs and time, and flexibly adjust production scales and prices based on market demand, passing on benefits to consumers. This will further promote the popularity and application of 5G-related equipment in various fields, driving the sustainable development of China's communications industry.

04

Starting with SAW and Building Momentum for BAW

In recent years, domestic manufacturers have actively invested in technological research and development and product innovation, achieving numerous accomplishments. Companies such as Microgate, ZTE Microelectronics, and Hoda Electronics are representatives in this field, with their progress primarily concentrated in the SAW filter domain. In this area, leading Japanese manufacturers have constructed process barriers through their IDM model. Despite this, domestic manufacturers have generally adopted self-built production lines for development, albeit at a relatively slow pace, with a market share of less than 5%.

In contrast, the situation in the BAW filter domain is more severe. BAW filters possess the highest technical barriers, with more complex processes than SAW filters. Furthermore, companies like Broadcom and Qorvo have established comprehensive patent layouts, posing significant challenges for domestic manufacturers seeking breakthroughs in this field. Currently, domestic manufacturers hold almost zero market share in the BAW filter market.

Hoda Electronics is the earliest company to engage in RF filter research and development. It possesses 0.25μm process technology, chip-scale packaging (CSP) technology lines, and wafer-level packaging (WLP) production lines, capable of producing duplexers with dimensions of 0.9x0.7 and filters with dimensions of 1.6x1.2. According to previous data, Hoda Electronics' surface acoustic wave filters and duplexers have passed validation and achieved mass production sales through mobile phone terminals and ODM manufacturers such as Xiaomi, OPPO, Huawei, Huqin, Longqi, ZTE, and wireless communication module manufacturers.

Microgate began researching and developing filters in 2015 and achieved mass production in 2017. That same year, it formed a joint venture with the 26th Research Institute of China Electronics Technology Group Corporation (CETC), with CETC responsible for front-end processing and Microgate responsible for back-end packaging. Currently, it has the capability to mass produce both LTCC and SAW filters and plans to complete its RF filter expansion project by the end of 2024. Earlier this year, Microgate stated that its 5G LTCC filters are primarily used in communication base stations and have been sampled and tested by downstream customers. In a recent investor Q&A, Microgate indicated that its RF filter products can be applied to intelligent terminals such as T-Box in the Internet of Vehicles.

Sunway Communication established its subsidiary Sunway Microelectronics in 2016 to begin its layout in the RF front-end device business. In 2017, the company signed a 10-year strategic cooperation agreement with the 55th Research Institute of CETC, investing RMB 110 million to acquire a stake in Deqing Huaying and enter the domestic filter market. In 2020, SAW filters achieved shipments, and the company continued to invest in Deqing Huaying that year.

The 26th Research Institute of CETC is the only professional research institute in China dedicated to military acousto-optic technology research and development. It is the standard-setting unit for national military standards and industry standards for acousto-optic products and possesses R&D and production capabilities for SAW, TC-SAW, and FBAR.

ZTE Microelectronics has a relatively complete SAW R&D and design team. In 2020, it established a wholly-owned subsidiary, Xinzhuo Semiconductor, dedicated to the industrialization of filters. The 6-inch filter production line entered the process commissioning phase in Q1 2022 and entered small-scale mass production in the first half of 2022. By the end of 2022, the self-built filter production line had fully entered large-scale mass production. ZTE Microelectronics stated that as of the end of the first quarter of 2024, L-PAMiF and LFEM-related module products integrated with self-produced IPD filters have been validated and achieved mass production shipments at multiple clients.

The main business of CETC Deqing Huaying Electronics has expanded to three major product categories: surface acoustic wave devices, piezoelectric and optoelectronic crystal materials, and RF modules. Its primary research and development focuses on 3-8-inch lithium niobate and tantalate lithium niobate wafers, surface acoustic wave filters, surface acoustic wave sensors, circulators, and isolators.

San'an Optoelectronics' RF filter business encompasses Xiamen San'an Integrated Circuit Co., Ltd., and Quanzhou San'an Integrated Circuit Co., Ltd., making it the first domestic enterprise capable of providing a full set of quadplexers and duplexers required for the PhaseVNR architecture. Last September, San'an Optoelectronics stated on an interactive platform that the company had established a stable and mass-produced RF front-end professional foundry platform, with PA and filter products primarily used in mobile phones, and that new domestic mobile phones had been supplied in batches.

At the same time, some manufacturers have made breakthroughs in the BAW filter domain. Last year, SenseTime Microsystems announced that its controlled subsidiary, Silex Microsystems Technology (Beijing) Co., Ltd., had completed the small-batch trial production phase of a series of BAW filters manufactured using MEMS technology for a certain customer.

In the 4G era, due to the relatively mature industry, SAW and TC-SAW had certain cost advantages. However, in the 5G and higher-frequency communication era, BAW offers technical advantages such as higher frequencies and wider bandwidths, providing lower insertion losses, better selectivity, higher power capacity, larger operating frequencies, and better electrostatic discharge protection, resulting in superior performance in high-frequency application scenarios. Therefore, domestic RF manufacturers must not only join this battle but also give full play to their advantages, continuously increase investment in research and development, delve deeper into BAW filter technological innovations, and enhance product quality and performance to secure a place in both domestic and international markets, breaking the long-standing technical monopoly of foreign manufacturers and propelling China's RF filter industry to a higher level of development.