Low-Temperature Superconducting DC-Contact RF MEMS Switch for Cryogenic Reconfigurable RF Front-Ends

A niobium-based superconducting dc-contact RF microelectromechanical systems switch is introduced and is thoroughly analyzed. The switch is amenable to integration with superconducting microelectronics technology. A comparison of the switch's RF performance at room and cryogenic temperatures indicates a significant improvement in the insertion loss of the switch when niobium is superconducting. The mechanical characteristic of the switch at extremely low temperature (4 K) is also investigated. The switch exhibits an increase of 18% on the actuation voltage as the temperature changes from 293 K (room temperature) to 4 K. A niobium superconducting tunable resonator is designed and tested, employing the proposed switch as the tuning element in the form of a switched capacitor bank monolithically integrated with the resonator. The measured results at 4 K clearly indicate the discrete resonance frequency states of the resonator. A three-pole tunable bandstop filter is designed with a center frequency of 1.2 GHz and dimensions of only 5 mm × 1.2 mm. The results demonstrate a tuning range of 12% while maintaining an excellent RF response of the filter.