Advantages of MEMS Switching in Reconfigurable and Switch Filter Banks

Many systems require configurable RF filters. The switched filter bank architecture uses multiple predefined filters, such as band-pass, high-pass, or low-pass filters, each with a different frequency range, enabling fast, discrete frequency or band switching in applications such as wideband receivers, software-defined radios (SDRs), and test equipment. Typically, RF switching is provided by MEMS devices, PIN diodes, FETs, or relays.

Though PIN diodes offer fast switching times with high linearity and isolation, they are power hungry and require significant thermal management to dissipate the heat generated and complex biasing circuitry. As a result, PIN diode implementations require many external components and heatsinks, which consume considerable PCB real estate.

FETs also offer fast switching times, but they require a large, complex thermal design to avoid increased losses and degradation. Insertion loss is also higher than that of PIN diodes.

Electromechanical relays (EMRs) are comparatively slow, large, heavy, power-hungry, and have short operating lives. However, they are still widely used across hundreds of applications, including automated test systems and telecommunications equipment. In defense and mission-critical applications, EMRs require bulky, active thermal management—fans, heat pumps, or heatsinks — to withstand harsh operating conditions. Consequently, they are unsuitable for SWaP (Size, Weight, and Power) applications.

MEMS technology overcomes the issues associated with other RF switching technologies. It offers significant advantages over PIN diodes, FETs, and EMRs across a variety of metrics, including lower insertion losses, minimal heat generation, high isolation and high linearity, lifespans of billions of operations, while being significantly lighter and smaller. MEMS also requires minimal external components or thermal management, eliminating heatsinks.

Advances in MEMS switching

Traditionally, MEMS has been used in applications such as microphones, airbags, and sensing devices. Research and development in new materials and advanced manufacturing processes have facilitated the development of MEMS devices that deliver superior performance in RF switching applications, such as switched filter banks. These new devices have a much smaller footprint, low insertion loss, greatly reduced power consumption and highly reliable support of over 3 billion operations.

For example, tactical radios weighed around 54 pounds in the 1970s and, due to MEMS technology, are expected to weigh as much as an iPhone in the near future.

Figure 1:Improvements in switches have led to smaller,lighter,more efficient, and more capable tactical radios.

Metal fatigue as a point of failure in advanced MEMS switches has been essentially eliminated due to advances in metal alloys. In addition, advanced MEMS switch actuators are tiny and have negligible mass, enabling constant performance even during extreme shock and vibration, such as acceleration environments of 100 G and higher. EMRs tend to fail under these conditions.

Advanced MEMS switches also generate negligible heat, boosting power efficiency and eliminating the need for thermal management or heatsinks. Solid-state switches, while an improvement over EMRs for RF switching, still generate significant heat and continue to draw current even when not switching.

Menlo Micro, a General Electric spin-out, has developed a proprietary high-volume, low-cost manufacturing process that electrodeposits metal alloys onto a glass substrate to form an actuated beam contact with high conductivity, strong mechanical performance, and excellent reliability. Branded the 'Ideal Switch®,’ it actuates in under 10 µs, exhibits negligible resistance, and maintains high linearity from DC to 70 GHz. Furthermore, thousands of switches can be electrodeposited on a single die.

Ideal Switches® are fabricated using through-glass-via (TGV) packaging, which employs short, metallized vias to dramatically reduce switch size. The TGV packaging approach also eliminates wire bonds for high-frequency applications and reduces package parasitics by more than 75%. The process is additionally well-suited for high-volume, low-cost manufacturing.

Moreover, the technology also allows passives and other components to be integrated directly into glass, creating highly miniaturized RF subsystems. For high channel counts, controllers can be integrated as well, further reducing the need for external components.

Advantages of RF switching in switch filter banks

The trend in requirements for RF switch filter banks is towards lower power consumption and smaller size, despite systems adding more functionality. In aerospace and defense applications, SWaP is a primary design consideration. Using advanced MEMS switches instead of PIN diodes enables designers to realize up to 90% reduction in weight and 95% reduction in size. With a manufacturing process similar to that of semiconductors and the ability to integrate most external components, MEMS switch arrays can also deliver cost savings, reducing component count by up to 70% and significantly reducing BOMs while enhancing reliability.

With more compact and lower power consumption switched filter banks, designers can use a smaller PA and extend the battery life in systems such as tactical radios. In addition, the lower insertion loss of MEMS switches, from typically 3-4 dB to 1.4 dB, provides a 2 dB improvement in RF power budget—boosting radio range.

MEMS switches easily meet IEC 60601/60068 standards and withstand MIL-STD 810G/H vibration and shock, making them ideal for miniaturization in military RF applications. Smaller, more power-efficient switch filter banks lead to significant reductions in equipment size while boosting performance.

Figure 2: Traditional switch filter bank using PIN diodes versus an ideal switch 

MEMS in chip-scale packaging can replace multiple EMRs, where even large matrices of MEMS switches consume significantly less power than a single EMR. MEMS switches are 1000 times faster than EMRs, are typically over 90% smaller, and only consume tenths of milliwatts of power.

Advanced MEMS switches can also deliver an insertion loss delta variation of around 0.05 dB across temperatures from −40 to +150°C. They can withstand extreme cold, including liquid nitrogen temperatures at −196°C and the millikelvin range used in quantum-computing refrigerators (below 10 mK). Consequently, this broad temperature tolerance makes MEMS technology ideal for military aircraft and other defense platforms that experience rapid temperature cycling at both low and high altitudes.

MEMS opens up new applications

Advances in MEMS technology have enabled switch filter banks to significantly downsize and outperform PIN diodes, FETs, and EMRs, making them ideal for SWaP-constrained applications and enhancing reliability in RF test equipment by replacing EMRs. MEMS is crucial for miniaturizing switch filter banks and unlocking high-performance capabilities in nano- and microsatellites, automotive radar and V2X, massive MIMO and carrier aggregation, frequency-agile IoT networks, and 5G/6G base stations and handsets, particularly above 6 GHz. Looking ahead, ongoing MEMS innovations, including faster switching speeds, higher operating frequencies, energy-harvesting capabilities, and embedded AI/ML integration, are set to enable next-generation RF systems that are smaller, smarter, more energy-efficient, and far more capable than ever before.

About the Author:

Chris Keimel is Co-Founder and Chief Technology Officer at Menlo Micro, where he drives the company’s technical strategy and leads R&D on its metal-MEMS “Ideal Switch” technology. He originally helped to develop the platform at GE Global Research, advancing miniaturized relay structures for power and RF applications. Chris has authored multiple peer-reviewed papers and holds numerous patents in MEMS switching. He earned his B.S. from Cornell University.