It’s been obvious for decades that the microelectromechanical systems (MEMS) switch could potentially replace PIN diode, mechanical, FET, and other types of switches in a broad swath of RF and microwave applications. A MEMS switch has almost everything an engineer could ask for: It’s smaller and lighter than any other switch technology; has very little insertion loss; provides very high isolation; can operate well into the millimeter-wave region; has exceptionally low intermodulation distortion; and can handle reasonable amounts of RF power.
So why didn’t RF MEMS switches take the world by storm years ago? The answer lies in the obstacles that have defied developers’ efforts to tame them, primarily suitability for low-cost mass production and demonstrated reliability over billions of switching cycles.
However, it now appears that 35 years after IBM described the first “microelectromechanical” switch, and more than a quarter-century after Analog Devices introduced the world’s first commercial MEMS product (an accelerometer), the technology has finally overcome these hurdles. To understand why it took so long to get here, it’s important to understand the topsy-turvy development of the MEMS switch.
MEMS Memory Lane
IBM’s development marked the first time that semiconductor fabrication techniques were used to make tiny mechanical structures in silicon that were moved electrically. It showed that such a device could combine the benefits of semiconductor manufacturing processes with the inherent characteristics of electromechanical relays. The rewards were potentially so enormous, especially for defense systems, that Hughes Research Labs, Raytheon, Rockwell, and others devoted large sums of money and time to bring RF MEMS switches to fruition.
Their work solidified their belief that not only could these devices be smaller than even the smallest PIN diode, FET, or other solid-state switch, they could be orders of magnitude smaller than electromechanical types that, although invented before the Civil War, resigned supreme (and are still in use today). The next step seemed obvious: Refine the manufacturing process and solve reliability issues, and a few other less-thorny problems. After masses of journal papers were written, patents applied for, and other efforts by dozens of organizations throughout the world, commercial devices remained as far away as ever.
By this time, in the early 2000s, MEMS marketing had reached a fever pitch, promising that the remaining problems associated with MEMS switches would be soon swept away. Startups were formed to fabricate and develop commercial products, and defense and commercial customers awaited the outcome. What they got instead were sampled devices that delivered neither the required reliability or wafer-to-wafer consistency that had been promised.