Description: The development of cryogenic microwave components, such as focal plane polarization modulators, first requires an RF MEMS switching technology that operates effectively at cryogenic temperatures. The approach of this project is to explore the performance of capacitive MEMS switching technology at low temperatures. MEMS capacitive switches represent an alternative to ohmic contact switches, where the RF impedance of the device is not dependent on metal-metal contacts. These MEMS switches operate with much lower effective series resistance (generally ~ 0.25 ohms) and do not have the issues associated with dry contact switching. This technology also has the advantage of operating very well at millimeter-wave frequencies and higher, where many of the most demanding performance limitations exist. This technology has seen significant investment through DARPA and the DOD, and is directly applicable to high-performance microwave components needed in several of the upcoming NASA missions.

Benefits: One of the dominant applications of RF MEMS being pursued today is that of tunable or reconfigurable filters in the microwave and millimeter-wave frequency ranges. High performance waveguide filters are a staple of satellite and earth-based communications systems. Unfortunately, those high-performance filters are large, heavy, and expensive (each one is hand crafted). One excellent application of MEMS technology is making those filter tunable, so that a single filter can be reconfigured or adapted to changing requirements and usage. One excellent application of tunable filters is in cellular base station applications. Currently, transmitter head at cell phone sites have fixed channel filters which on occasion need to be changed out do to changing requirements in base station coverage or services. This requires manual replacement of filters, a significant logistics issue for both manpower and inventory to keep the 100,000+ US cell phone sites updated. A tunable filter would enable remote retuning of filters to save significant expense. The development of this cryogenic switch technology would be compatible with the superconducting filter technology and offer some very interesting product capabilities for tunable, superconducting filters.

Low-loss, low-power microwave and millimeter-wave switching devices are very important to the development of a variety of NASA sensors and communications systems. In sensors, this RF MEMS technology will be very useful in radiometer systems. Using MEMS to switch polarizations in focal plane detectors is one very useful function. This is especially true for bolometric detectors, where very low loss and low power dissipation devices are required. The MEMS provide a convenient platform for routing and phase shifting the microwave or millimeter-wave signals being sensed. Applications include earth-based monitoring for xxx and space-based survey missions, including PATH, SCLLP, GACM, and the Beyond Einstein Inflation Probe for probing the cosmic microwave background emission.