Design and Fabrication of a Tunable Superconductive Resonator Utilizing Micromachined Tunable Capacitor

This paper presents the design, fabrication, and characterizations of a flip-chip-bonded micromachined capacitor for tuning a high-temperature superconductive resonator. The major issue of the tunable superconductive resonator is its high driving voltage due to the accumulated thermal stresses and the sensitivity of the superconductive material to the fabrication process. The tunable capacitor in the form of a microbridge with flexible boundaries is proposed to reduce thermal stress. Thermal stress is reduced to 10 MPa, and the pull-in voltage of the capacitor is 25 V. The micromachined capacitor and the superconductive resonator are fabricated separately and then integrated together by using a flip-chip-bonding technique. This integration method prevents the superconductor material from the high-temperature process. At 75-K operation temperature, the measured center frequency of the fabricated tunable resonator changes from 2.93 to 2.87 GHz when the driving voltage increases from 0 to 40 V.