Will the ideal switch based on MEMS technology turn on?

    Twenty years ago, engineers specializing in radio frequency circuits imagined an "ideal switch." When this kind of switch is "on", it will have ultra-low resistance, when "off" it will have ultra-high resistance, and so on. It is small, fast, easy to manufacture, capable of switching considerable current, able to withstand billions of on-off cycles, and requires very little power to work. It can transmit signals to tens or even hundreds of MHz without distortion (near perfect linearity).

    This is not a whimsical thing. There is already a market ready for this kind of change in the emerging large industries. With the breakthrough of micro-electromechanical systems (MEMS), major projects have spread throughout the United States and Europe. Many are funded by the Defense Advanced Research Projects Agency or the European Union Network of Excellence.

    And now, after a longer and more turbulent technological development effort, the RF MEMS switch has finally appeared on the road to commercial success.

In the United States, especially the two companies seem to have established a firm foothold in the fast-growing and highly competitive market. One is Menlo Micro, a subsidiary of GE Ventures in Irvine, California. The company's co-founder and senior vice president Chris Giovaniello said that they have more than 30 customers in the aerospace, military and wireless infrastructure industries.

    At the same time, Cavendish Kinetics, which was acquired by Qorvo, a leading wireless device and system manufacturer, was established in October last year to develop RF MEMS switches for use in smartphones and other fields. Neither party has announced the specific terms of the transaction, but Cavendish has raised more than $58 million in at least three rounds of financing (Semiconductor giant ADI also sells RF MEMS switches for test and instrument applications.)

    After the long and turbulent intermittent hopes were dashed, the RF MEMS switch was a success. "After many, many companies' attempts, we succeeded in these two. In the process, maybe 20 companies went bankrupt and caused fierce competition," said Gabriel Rebeiz, a pioneer in RF MEMS research and development and the University of California. Professor of Electrical Engineering at the University of San Diego.

    "For technology startups, a 10% success rate is normal."

    The new device combines some of the best features of electromechanical relay switches (ultra-low resistance and leakage current and very high linearity) with some of the advantages of semiconductor switches: small size, very high reliability and robustness. Conceptually, they are similar to relay switches. In operation, the electrostatic force pulls a conductive beam called an actuator or cantilever towards the electrical contacts. Unlike relays, which are triggered by electromagnets, RF MEMS switches use a simple DC voltage in the range of 50 to 100 volts to generate an electrostatic field that draws a beam of electrons to the contacts. (The relatively high voltage comes from a DC-DC converter powered by a circuit voltage of 3V to 5V.) Since the magnetic field is static, the current and power consumption are very low.

    Giovaniello said that one of the most difficult technical challenges is to find a conductive alloy that can withstand billions of bending processes. He said: "The real problem is the actuator." "This is where GE has invested a lot of energy in developing alloys. We have developed some proprietary alloys with high conductivity, which are really suitable for relays. But their The mechanical strength is extremely high, almost like polysilicon.

    He added: "For decades, GE has done a lot of work on alloys used in jet engines. In fact, some of them helped us solve some basic reliability problems." Menlo has not disclosed the composition of its alloys, but A research paper written by GE and Menlo engineers about five years ago indicated that they were using separate alloys of nickel and gold.

　Giovaniello said that some of Menlo’s customers are using these devices (approximately 50 x 50 microns in size) in wireless base stations, military radios or phased array radars. Advanced radio and wireless systems are increasingly dealing with many different frequency bands, each of which is "selected" by one or more different filters. He said: "Our customer RF has 20 filters." "When you have to use traditional switches to choose between many filters, selecting all the different filters through all the switches will cause a lot of loss. He explained that the total power loss is 3 to 4 decibels, and pointed out that a reduction of 3 dB means a loss of up to 50%.

    At the same time, Qorvo's goal is the application inside the smartphone (the same is true for Menlo Micro). Zhu Julio Costa, Qorvo's senior director of technology development, said that this is a huge market, with about one billion smartphones sold every year, but the requirements for components are also extremely strict. "Your phone is an important part of your daily life, so if [the new component] is unreliable, it will not be merged."

　Costa explained that there are two obvious possible uses for devices in smartphones. The first thing Qorvo pursues is antenna tuning.Modern smartphones have up to eight antennas to accommodate the many frequency bands that continue to grow as wireless networks transition from 4G to 5G. In order to better match the antenna to the frequency, the switch embedded along the antenna can change its configuration, and it can also be switched to a resonant device such as a capacitor or inductor to fine-tune the antenna's response. For this application, mobile phone manufacturers now use semiconductor switches based on silicon-on-insulator (SOI) technology. However, MEMS devices may have higher frequencies and linearity, making them an attractive alternative, especially for certain 5G frequency bands, Costa said. He hopes to see mobile phones integrate these switches in "within a few years."

　In Europe, long-term R&D projects are not far behind. A start-up company called AirMems is marketing RF MEMS switches based on the work of the University of Limoges in France. In Germany, during the development process of the Institute IHP (High Performance Microelectronics Innovation), the RF MEMS switch is integrated directly to the bipolar CMOS chip.

　Giovaniello said in an extensive interview that wireless, radar and instrumentation applications are just the beginning. He announced that Menlo Micro has managed to conduct 20 amperes of current through one of the micro switches, and he envisions that the device will function as a "resettable, electronically controlled fuse" in the future.

He added: "Every few generations, there will be a new technology that provides you with a different way of making switches." "100 years ago there were only mechanical equipment, then vacuum tubes, then transistors, and then integrated circuits. If you think about it, they are all different ways to switch.

    "This is how we like to describe this ideal switch technology. It is a combination of the best in the field of machinery and semiconductors, but in the end, it is a new process technology for making switches that will enable us and our cooperation Partners will produce hundreds of different products in the next ten years."

This article is from Allicdata Electronics Limited which offer electronic components, semiconductors, antennas, capacitors, connectors, diodes, transistors, IC,resistors. For more product information, please go to the website to get it.