Josephson Oscillators Based on Amorphous Superconductors

Thin films of amorphous Mo _x Ge _{1- x} grown with magnetron sputtering are known to exhibit excellent homogeneity and fairly high superconducting transition temperatures (up to 7.5 K). These properties make MoGe thin films suitable to form high-quality tunnel junctions, as demonstrated recently by our group [see Supercond. Sci. Technol. 35, 035008 (2022)]. Here, we report the experimental demonstration of an MoGe/Al/AlO _x /(Al)MoGe Josephson oscillator based on amorphous superconductor MoGe, which allows for continuous tuning of the oscillation frequency from about 1 GHz up to tens of GHz. We believe such an oscillator may be useful as a compact on-chip microwave source suitable to control some types of qubits based on Josephson junctions.