Compact superconducting microwave resonators based on Al-AlOx-Al capacitor

We address the scaling-up problem for superconducting quantum circuits by using lumped-element resonators based on an alternative fabrication method of aluminum -- aluminum oxide -- aluminum ($\mathrm{Al/AlO_x/Al}$) parallel-plate capacitors. The size of the resonators is only 0.04~$\mathrm{mm^2}$, which is more than one order smaller than the typical size of coplanar resonators (1~$\mathrm{mm^2}$). The fabrication method we developed easily fits into the standard superconducting qubits fabrication process. We have obtained capacitance per area 14~fF/$\mathrm{\mu m^2}$ and the internal quality factor $\mathrm{1\times 10^3 - 8\times 10^3}$ at the single-photon level. Our results show that such devices based on $\mathrm{Al/AlO_x/Al}$ capacitors could be further applied to the qubit readout scheme, including resonators, filters, amplifiers, as well as microwave metamaterials and innovative types of qubits, such as $0-\pi$ qubit.