The two types of MEMS switches — metal-to-metal contact and capacitive — are prone to failure because of sagging cantilever structures. Metal-to-metal contact switches consist of a metal transmission line and a metal bridge/cantilever that are separated by an air gap. The metal contacts in these switches are susceptible to wearing down and welding over time. Capacitive switches use both a thin insulator and an air gap between the transmission line and the bridge/cantilever, preventing the two metal structures from touching in an effort to stop the metal connects from welding together. Both of these types suffer from their reliance on metal bridge/cantilever structures that are prone to severe sagging and eventual failure through prolonged operations.
NASA’s Glenn Research Center has developed a radio frequency microelectro-mechanical systems (RF MEMS) switch that overcomes this problem through the use of thin film, stress- and conductivity-controlled, non-metallic bridge/cantilever structures that are extremely resistant to sagging and failure. The improved performance and reliability of the RF MEMS switch can greatly benefit wireless communications systems, phased-array antennas, filter banks, programmable attenuators, relays, and micro-switches.
The device uses non-metallic cantilevers/bridges as the main mechanical component, which significantly improves the RF characteristics and dramatically enhances the reliability of the switch. The device can withstand and operate in harsh environments, survive high-power applications, and be assembled into various configurations.
Glenn’s technology supplants metallic cantilevers and/or bridges with ones fabricated with silicon carbide (SiC), which is an ideal material for these bridges/cantilevers because of its inherent stiffness and tensile stresses that result in beams that are completely resistant to sagging and failure. In addition, SiC is highly resistant to oxidation and chemicals, so its surfaces remain virtually stiction-free, a significant advantage when the material is fabricated into narrow-gapped, micromachined bridges for use in contact switches.
A thin metal layer is placed over the SiC bridge for biasing the device. Because there is no need for an additional layer of insulating film to prevent stiction, the device can use a low-voltage DC bias for actuation instead of the low-frequency peak-to-peak voltage waveform most capacitive MEMS switches require. This switch can be assembled into a number of different configurations, including single-pole single-throw (SPST), single-pole double-throw (SPDT), and as many throws as the layout permits.