Radio Frequency Microelectromechanical System (RF-MEMS) is one of the most important applications of MEMS technology. It is also a research hotspot in the field of MEMS since the 1990s. RF MEMS is used in signal processing in RF and microwave frequency circuits. It is a technology that will have a significant impact on the existing radar and radio frequency structures in communication.
RF MEMS devices can be classified into the following categories according to device types:
   Phase shifter, adjustable filter and variable beam antenna based on switch basic structure unit
   High Performance Silicon-based/Fused Quartz-based Filters
   Ultra-Miniaturized Acoustic Wave Filters (SAW, FBAR)
   Antenna Array with Micro-nano Inductance and Capacitance Structure

High Performance T/R Modules Composed of Micro-nano Transmission Line/Waveguide Structures (e.g. Micro-coaxial Structures)
RF MEMS has been widely used in military and civil fields, including personal communications, such as mobile phones, PDA (Personal Digital Assistant), data exchange of portable computers, vehicle-borne, airborne, ship-borne transceivers and satellite communication terminals, GPS receivers, information-based operational command, battlefield communications, miniaturized satellite communication systems, phased array radar, etc.
With the development of the fifth generation mobile communication (5G), there is an urgent need for some new planar devices with low power consumption, miniaturization and integration with signal processing circuits. It is hoped that they can cover the broadband including microwave, millimeter wave and sub-millimeter wave. At present, there are still a large number of indispensable off-chip discrete components in the communication system, such as inductors, variable capacitors, filters, couplers, phase shifters, switching arrays and so on, which become the bottleneck to further reduce the size of the system. The emergence of RF MEMS technology is expected to solve this problem. Passive devices manufactured by RF-MEMS technology can be integrated directly with active circuits in the same chip to achieve high on-chip integration of radio frequency systems, eliminate parasitic losses caused by discrete components, truly achieve high cohesion and low coupling of the system, and significantly improve the performance of the system.

Technological leaders in the field of RF MEMS are mainly high-tech enterprises in the United States, Japan and Europe. Research institutions include HRL Laboratories, LLC, Royal Society of Chemistry, Texas Instruments, University of Michigan-Ann Arbor, UC Berkeley, Northeastern University, MIT Lincoln, Analog Devices, Raytheon, Motorola, etc. Major suppliers include Avago, Rad. ENT MEMS, XCOM Wireless, WiSpry (acquired by Raytheon), RFMD (Qorvo), Delf MEMS, OMRON, Toshiba, MEMTronics, etc.
Avago
   In 2015, Avago acquired Bloom. In the market of MEMS filter, Avago occupied 87% of BAW filter market, basically forming a monopoly situation.
   BAW filters, the highest operating frequency can reach 20 GHz, 5G era for BAW filters is simply tailor-made, but the shortcomings of BAW filters are obvious, that is, expensive.
Radent MEMS
   The company is a manufacturer of aerospace and military RF equipment. With the support of DARPA, the U.S. Department of Defense, the company has increased the reliability of MEMS switches to 1.5 trillion times. The company provides band selective switching for various receiving and transmitting chains and phase shifters.
XCOM Wireless
   The company is a manufacturer of microwave radio frequency relays. It mainly produces chips and packaging tuning circuits and microwave relays 
WiSpry
   In 2016, it was acquired by Raytheon Technologies. The main product is RF-MEMS antenna tuner with high performance.
RFMD (Qorvo)
   RFMD and Triquint merged into Qorvo in 2015. The company’s BAW filters are designed for ultra-small, high-performance applications such as smartphones, consumer electronics wireless terminals, micro-and nano-satellites.
DelfMEMS
   The company’s main RF MEMS switch, the company’s ohmic contact switch after testing can withstand more than 1 billion switching cycles.
OMRON
   The main RF MEMS products are SAW filters. SAW filters are mainly aimed at the frequency bands below 2GHz, such as early 2G communication.

Toshiba
   Toshiba’s RF MEMS products are mainly some basic devices, such as switches, MOSFETs, transistors and diodes.
MEMTronics
   MEMTronics is a Waferless RF manufacturer. Its main products include MEMS phase shifters and tunable filters.
   The domestic research on RF MEMS began in the late 1990s. The main research institutions are Tsinghua University (switch, filter), Peking University (switch), 13 Zhongdian and Mattel Technology Company (filter), 55 Zhongdian (filter, switch), Southeast University (microwave structure design), Zhejiang University (theoretical analysis), Tianjin University and ZTE Communications Company.（ FBAR filter, Institute of Electronic Engineering of the Chinese Academy of Sciences and University of Electronic Sciences (THz filter), Shanghai Institute of Microsystems of the Chinese Academy of Sciences, Institute of Microelectronics, Institute of Electronics, etc. The filter products of 13 and 55 Zhongdian power plants are the main ones that have achieved good practical application. Most of the other devices are still in the laboratory research stage.
summary
   The research of RF MEMS in China started relatively late, and 5G is a great challenge to RF MEMS, which is also an opportunity and challenge for RF MEMS manufacturers in China. On the one hand, there are few test reports on the application of RF MEMS in 5G. Major manufacturers have not started to study it yet. Chinese manufacturers can seize this opportunity to overtake in bends. On the other hand, the research and development of RF MEMS is very difficult, and enough efforts are needed to achieve overtaking in bends.