Epitaxial Al2O3 capacitors for low microwave loss superconducting quantum circuits

Abstract

We have characterized the microwave loss of high-Q parallel plate capacitors fabricated from thin-film Al/Al2O3/Re heterostructures on (0001) Al2O3 substrates. The superconductor-insulator-superconductor trilayers were grown in situ in a hybrid deposition system: the epitaxial Re base and polycrystalline Al counterelectrode layers were grown by sputtering, while the epitaxial Al2O3 layer was grown by pulsed laser deposition. Structural analysis indicates a highly crystalline epitaxial Al2O3 layer and sharp interfaces. The measured intrinsic (low-power, low-temperature) quality factor of the resonators is as high as 3 × 104. These results indicate that low-loss grown Al2O3 is an attractive candidate dielectric for high-fidelity superconducting qubit circuits

Material matters in superconducting qubits

“…Generating heteroepitaxial arrangements of superconducting metallization on select substrates provides a path to minimizing microstructural defects, such as grain boundaries, present in polycrystalline films. For example, Re (0002) films are closely matched to c-plane sapphire substrates, but with a 30 0 in-plane offset [101]. CPW resonators composed of Re [197] and Al [198] have been fabricated on sapphire through the use of elevated temperature depositions.…”

“…FIG. 5: Comparison of loss tangents extracted from measurements below 100 mK for (a) SiOx [75], [98], [99], AlOx [100][101][102][103], SiNx [104], amorphous Si [75], [98] and MgO [75] dielectric films, and (b) single crystal substrates [105]- [107]. A wide range of values can be observed due to differences in fabrication and the corresponding impurity levels and defectivity.…”

Rhenium Metal and Rhenium Nitride Thin Films Grown by Atomic Layer Deposition

“…Although rhenium is rare and can be difficult to synthesize, various methods have still been employed to grow particles, powders, thin films, and coatings. These techniques include chemical vapor deposition (CVD), chemical vapor infiltration (CVI), pulsed laser evaporation (PLE), electron‐beam evaporation, electrodeposition, molecular beam epitaxy (MBE), and magnetron sputtering . Even more limited has been the preparation of rhenium nitrides which have been synthesized by sputtering, ion implantation, pulsed laser deposition, and high‐pressure solid‐state metathesis .…”

Rhenium Metal and Rhenium Nitride Thin Films Grown by Atomic Layer Deposition

“…Although rhenium is rare and can be difficult to synthesize,v arious methods have still been employed to grow particles,p owders,t hin films,a nd coatings.T hese techniques include chemical vapor deposition (CVD), [7,12] chemical vapor infiltration (CVI), [15] pulsed laser evaporation (PLE), [16] electron-beam evaporation, [12] electrodeposition, [5] molecular beam epitaxy (MBE), [8] and magnetron sputtering. [17] Even more limited has been the preparation of rhenium nitrides which have been synthesized by sputtering, [18,19] ion implantation, [20] pulsed laser deposition, [21] and high-pressure solid-state metathesis. [22,23] There is thus still room for introducing new methods for preparing these intriguing refractory/noble metal materials to make them more widely available for various applications using highly controllable methods with moderate deposition conditions.…”