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RF MEMS basics: 5 questions answered

The market for microscopic mechanical systems for mobile devices appears to be gaining momentum, so RCR Wireless News takes a closer look at the ecosystem and some RF MEMS basics.

What are MEMS and RF MEMS?
MEMS are micro electro-mechanical systems – microscopic devices that rely on mechanical movements. According to Lars Johnsson, VP of product marketing for RF MEMS vendor Cavendish Kinetics, there are two classes of MEMS, including positioning-type MEMS such as gyroscopes and accelerometers that are frequently found in devices such as smartphones and tablets. Johnsson considers this a developed ecosystem with a number of vendors. An emerging MEMS category is that of Radio Frequency MEMS.

RF MEMS are manufactured much the same way as semiconductors and are placed in the RF signal path. Some RF MEMS, such as those made by Cavendish, are tuning solutions; and some RF MEMS are switches. As RF MEMS vendor DelfMEMS described it, “there are various types of RF MEMS components, such as CMOS integrable RF MEMS resonators and self-sustained oscillators with small-form factor and low-phase noise, RF MEMS tunable inductors, and RF MEMS switches, switched capacitors and varactors. RF MEMS switches operate in a similar way to conventional RF mechanical relays, but on a silicon chip-size scale.”

What are RF MEMS used for?
Johnsson said that he sees three areas in which RF MEMS will be or are being used in mobile devices, particularly in relation to antennas: to solve engineering issues related to the size and components of smartphones; being able to cover multiple bands and support carrier aggregation in disparate bands; and support beamforming on the device side rather than primarily on the cell base station side.

Devices, he noted, are getting thinner and thinner, so antennas are being squeezed even as the length and width of devices are expanding.

“Having an antenna you can tune helps with the size-constraint issues,” he added.

Johnsson said that RF MEMS have been a known technology for about 40 years, but it wasn’t until recently that they could be built in a small enough size, with high reliability and cost-effectively enough to be put into widespread use in mobile devices. According to recent news from Stats ChipPac, whose technology Cavendish leverages for its RF MEMS tuners, Cavendish’s tuners are already in half a dozen smartphones used in China, North America and Europe.

What advantages and challenges come with RF MEMS?
RF MEMS offer the potential for using less power, improving antenna performance and radiated power, and reducing  power loss in the system.

Still, Johnsson noted, RF MEMS also offer a challenge in terms of testing:Because they are physical devices, there is the possibility that they will wear out. That reliability aspect has been one of the challenges for RF MEMS applications. Cavendish announced earlier this year that its tuners passed 100 billion cycle lifetime testing, or as the company put it, that the device has a “virtually unlimited lifetime.”

“Reliability concerns have been a major adoption hurdle for RF MEMS for tuning, but Cavendish has worked hard to make reliability a non-issue, allowing OEMs to provide better performing smartphones using RF MEMS antenna tuners,” said Chris Taylor, director for RF and wireless components at Strategy Analytics, in a statement at the time. “Most LTE smartphones use antenna tuning to meet OEMs’ and operators’ performance targets across multiple bands, which has been a big challenge. Compared to tuners fabricated in CMOS SOI and GaAs p-HEMT technology, RF MEMS can provide substantially lower insertion loss and higher [Q factor or quality] for better antenna performance.”

What is the status of the RF MEMS market?
Last year saw the RF MEMS market build considerable momentum. Cavendish raised $7 million in a funding round late last year. DelfMEMS, another RF MEMS startup, received a similar amount in mid-2014 and announced a new RF MEMS switch product at MWC this year. RF MEMS vendor WiSpry announced earlier this year that its RF MEMS technology had been used by Skyetek to develop the first RF MEMS-enabled radio frequency identification reader.

A TechNavio report from this year expects a compound annual growth rate for the overall RF MEMS market of nearly 17% between 2013 and 2018, adding that the technology is “expected to penetrate the 3G and the 4G mobile market, especially in the developing countries. It facilitates engineers in designing devices that can integrate with the existing technology.”

According to the report, “increased usage of RF MEMS in smart devices is one of the major drivers of the market. Over the past few years, there has been unprecedented growth in the adoption of RF MEMS in smartphones. The demand is expected to grow as RF MEMS provide fast data transfer and enhanced network operations in smart devices. The cellphone manufactures are increasingly adopting the technology because of its size and compatibility, along with reduced cost per unit.”

Who are some of the RF MEMS players?
In the TechNavio report on the state of the market, named players in the RF MEMS market included Cavendish Kinetics, DelfMEMs, MEMtronics, Radant MEMS and WiSpry.


Kelly Hill
Kelly reports on network test and measurement, as well as the use of big data and analytics. She first covered the wireless industry for RCR Wireless News in 2005, focusing on carriers and mobile virtual network operators, then took a few years’ hiatus and returned to RCR Wireless News to write about heterogeneous networks and network infrastructure. Kelly is an Ohio native with a masters degree in journalism from the University of California, Berkeley, where she focused on science writing and multimedia. She has written for the San Francisco Chronicle, The Oregonian and The Canton Repository. Follow her on Twitter: @khillrcr

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