A novel micro-fabrication process for integration of Superconductor niobium-based RF circuits with gold-based RF MEMS devices

A novel 8-mask fabrication process for the integration of Low Temperature Superconducting (LTS) niobium (Nb) RF circuits with gold-based RF MEMS switches is proposed. A fixed and a tunable 3-pole bandpass filter (BPF) are fabricated implementing the new Nb-based fabrication process. The tunable BPF includes nine dc-contact RF MEMS switches. The center frequency of the tunable BPF shifts from 10 GHz to 9 GHz when the three switches that change the length of the resonators are in the `on´ state and the other six are in the `off´ state. The first version of the tunable BPF is all gold-based, which is measured at room temperature. The insertion loss of the all gold-based tunable BPF is close to 5.5 dB. The switches actuation voltage is around 32 V at room temperature. The fixed version of the BPF is fabricated using Nb as the lossless metal layer. Measurement of the fixed Nb-based BPF shows 4.4 dB improvement in the insertion loss at 4 K. The tunable version of the superconducting BPF is also fabricated and measured at 4 K. There is 1 GHz shift in the center frequency of the filter when the three RF MEMS switches are actuated. The actuation voltage of the gold-based RF MEMS switches at 4 K is about 48 V.