Microwave Product Digest – November 23, 2022
RF switches may not get the same level of attention as their more technologically glamourous counterparts like RFICs and MMICs, mmWave SoCs, and phased-array antennas, but they arguably play an equally important role in wireless infrastructure. That’s especially true today, as wireless carriers add new bands to the large number already in service. And as just so much room is available in these subsystems, it’s essential for every component to meet increasingly stringent demands. So, it should be no surprise that research and development of advanced materials, processes, and other efforts continue apace, with the most formidable being MEMS technology.
Today’s base stations have bulky, unreliable and power-hungry electromechanical relays (EMRs) that drive up power consumption, generate heat, take a considerable amount of space, and typically require coaxial interconnects. In some cases, this requires active thermal management that is necessary to ensure that they will survive. These components not only significantly increase system cost and complexity, but also aren’t well suited to small platforms such as small cells for which issues such as power consumption, size, and weight are critical metrics. And as systems shrink thanks to the “digitalization” of previously analog functions, EMRs have become a significant obstacle in the path of realizing 5G.
What’s long been needed is an alternative that does not suffer from the traditional electromechanical switch’s limitations while also providing better overall performance in a fraction of their size, with negligible power consumption and much longer operating lives. MEMS technology satisfies these requirements and many others, as well.
The closest competitor to MEMS are solid-state switches that are small, fast, and reliable but are also comparatively power inefficient and, to a lesser extent than their traditional electromechanical counterparts, generate heat that can require heat sinks and complex thermal management. Semiconductors are never fully “off,” and the resulting leakage currents waste power. Researchers throughout the world have been attempting for years to overcome the shortcomings of both traditional electromechanical and solid-state RF switches, but the result, until recently, has been a series of compromises rather than an ideal solution.
New (and Challenging) Applications for MEMS
MEMS technology has been employed for decades for a wide variety of applications, but for RF switching it is comparatively new, and a history of its development over two decades is littered with more than a dozen companies that tried and failed to solve the vexing challenges this technology presents.
MEMS switches have movable parts (a fundamental feature of MEMS in general) like their EMR counterparts, but in every other way a MEMS switch is almost entirely different. They are microscopic, are created on a wafer in a semiconductor fab, and have virtually no mass (Figure 1). In fact, they’re also different from any other MEMS application, so much different that developing and commercializing a reliable MEMS switch product has eluded researchers for more than 40 years. These efforts consumed the resources of many companies, causing nearly all of them to exit the field before they could achieve commercial success.