RF MEMS switches have proven their ability to operate under extremely harsh temperature, shock, and vibration environments and have debunked the long-standing belief that they were not robust enough to provide the operating life required in demanding applications.
When MEMS technology was first realized in production devices it didn’t take long before it displaced legacy technologies at a rapid pace, and today represents a global market size of at least $12 billion that’s growing at a rate of more than 9 % per year. However, until recently, there remained one major application, RF switching, that had not been addressed after more than a dozen companies spent over two decades trying to solve it. What is ironic today is that by taking a different approach, RF MEMS switches are not only meeting the reliability requirements of the most demanding applications, but deliver better performance in harsh environments and extreme operating conditions as well.
These advances could not have come at a better time, as virtually every market demands components that are smaller, lighter, and consume less power that can be produced in high-volumes and are extremely cost-effective. And they must also have very long operating lifetimes even when exposed to broad and varied temperatures, shock and vibration, and other onerous environmental factors.
Even though the electromechanical relay (EMR) is comparatively slow, large, and heavy, has a short operating life, and consumes lots of DC power, it remains widely used and a mainstay of automated test systems, telecommunications equipment, defense system, and dozens of other applications. Active thermal management techniques, such as fans, heat pipes, and large heatsinks, are often required to ensure electronic components can operate and survive in these extreme environments, driving up system cost and complexity. Nevertheless, EMRs pose challenges for deployment in small platforms, in which issues such as power consumption, size, and weight are critical metrics.
For example, consider a fighter aircraft in which there can be hundreds of RF switches and EMRs relays that collectively take up an outsize amount of space considering their function. In some cases they can consume hundreds of watts of power, are often heavy, low, and need to be replaced after just a few million switching operations. In contrast, multiple EMRs can be replaced by MEMS switches housed in a 2.5 x 2.5 x 0.9 mm chip-scale package, and even when employed in huge switch matrices consume less DC power than a single EMR alone. A MEMS switch not only switches 1000 times faster but is at least 90 % smaller, consumes almost no power, and can survive more than 3 billion switching operations even when handling relatively high RF power levels.
In addition, although solid-state switches are indeed small, fast, and reliable, they can be power inefficient and generate excessive heat requiring large, bulky heat sinks and complex thermal management. Additionally, semiconductors are never fully "off" resulting in leakage currents that waste power. Engineers have been trying to overcome the shortcomings of both EMRs and solid-state RF switches for years, but the end result has been a series of compromises rather than an ideal solution.
The solution that made MEMS switches viable for RF applications are the result of initial research conducted by General Electric, and spun out in the Irvine, CA-based startup - Menlo Micro. Menlo Micro is pioneering MEMS switch development for RF and power systems, and is calling their technology the “Ideal Switch”. The goal was to develop a high performance switch technology that could meet the demanding challenges of extreme operating environments, without sacrificing performance.
Existing MEMS-based switches were unreliable under harsh environmental conditions, and Menlo Micro designed its own ohmic MEMS switch from scratch, going so far as to develop an advanced proprietary fabrication process using electrodeposited alloys. The result is an electrostatically actuated beam/contact structure that combines mechanical properties near those of silicon with the conductivity of a metal.
The Ideal Switch can handle kilowatts of power and high-temperatures, with an operational lifetime of decades. Menlo Micro’s switches are fabricated using Through Glass Via (TVG) packaging (using short, metallized via holes) which enables a dramatic reduction in switch size, eliminating wire bonds for RF and microwave applications that also reduce package parasitics by more than 75 %. This allows for the current switch portfolio to operate from DC to 26 GHz, with upcoming designs pushing past 60 GHz in operating bandwidths.