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arXiv:2302.13930 · Physical Review Applied

NbN films with high kinetic inductance for high-quality compact superconducting resonators

Simone Frasca, Ivo Arabadzhiev, Sebastien Yves Bros de Puechredon, Fabian Oppliger, Vincent Jouanny, Roberto Musio, Marco Scigliuzzo, Fabrizio Minganti, Pasquale Scarlino, Edoardo Charbon A

Published Oct 9, 2023• 37 citations
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Abstract

Niobium nitride ($\mathrm{Nb}\mathrm{N}$) is a particularly promising material for quantum technology applications, as it shows the degree of reproducibility necessary for large-scale superconducting circuits. We demonstrate that resonators based on $\mathrm{Nb}\mathrm{N}$ thin films present a one-photon internal quality factor above ${10}^{5}$ maintaining a high impedance (larger than $2\mathrm{k}\mathrm{\ensuremath{\Omega}}$), with a footprint of approximately $50\ifmmode\times\else\texttimes\fi{}100\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}{\mathrm{m}}^{2}$ and a Kerr nonlinearity of few tenths of a hertz. These quality factors, mostly limited by losses induced by the coupling to two-level systems, have been maintained for kinetic inductances ranging from tenths to hundreds of picoHenry per square. We also demonstrate minimal variations in the performance of the resonators during multiple cooldowns over more than nine months. Our work proves the versatility of niobium nitride high-kinetic-inductance resonators, opening perspectives towards the fabrication of compact, high-impedance, and high-quality multimode circuits, with sizable interactions.

DOI
10.1103/physrevapplied.20.044021

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Niobium nitride (NbN\mathrm{Nb}\mathrm{N}NbN) is a particularly promising material for quantum technology applications, as it shows the degree of reproducibility necessary for large-scale superconducting circuits. We demonstrate that resonators based on NbN\mathrm{Nb}\mathrm{N}NbN thin films present a one-photon internal quality factor above 105{10}^{5}105 maintaining a high impedance (larger than 2k\ensuremathΩ2\mathrm{k}\mathrm{\ensuremath{\Omega}}2k\ensuremathΩ), with a footprint of approximately 50\ifmmode×\else\texttimes\fi100\ensuremath\mum250\ifmmode\times\else\texttimes\fi{}100\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}{\mathrm{m}}^{2}50\ifmmode×\else\texttimes\fi100\ensuremath\mum2 and a Kerr nonlinearity of few tenths of a hertz. These quality factors, mostly limited by losses induced by the coupling to two-level systems, have been maintained for kinetic inductances ranging from tenths to hundreds of picoHenry per square. We also demonstrate minimal variations in the performance of the resonators during multiple cooldowns over more than nine months. Our work proves the versatility of niobium nitride high-kinetic-inductance resonators, opening perspectives towards the fabrication of compact, high-impedance, and high-quality multimode circuits, with sizable interactions.
Nonlinear resonators of superconducting thin-film kinetic inductance have attracted considerable research interest in the fields of detectors, qubits, parametric amplifiers, and more. By tuning the deposition parameters, niobium titanium nitride (NbTiN) films (∼12 nm in thickness) present high resistivity(∼2000 μΩ cm) and large sheet kinetic inductance (∼0.7 nH/□). We designed resonators with NbTiN micronwire as the inductor and aluminum as the capacitor, which result in a high internal quality factor and a Kerr nonlinearity of a few hertz. The radio frequency response of the resonators demonstrates nonlinear behavior similar to that of the cubic Duffing oscillator, including frequency shift and hysteresis region. The kinetic inductance resonator is a promising candidate for high saturation power parametric amplifiers.
Superconducting resonators with high-kinetic inductance play a central role in hybrid quantum circuits, enabling strong coupling with quantum systems with small electric dipole moment and improved parametric amplification. However, optimizing these resonators simultaneously for high internal quality factors (QiQ_iQi​) and resilience to strong magnetic fields remains challenging. In this study, we systematically compare superconducting resonators fabricated from niobium nitride (NbN) and granular aluminum (grAl) thin films, each having similar kinetic inductance values (Lk∼100L_k \sim 100Lk​∼100 pH/sq). At zero magnetic field, resonators made from grAl exhibit higher QiQ_iQi​ compared to their NbN counterparts. However, under applied magnetic fields, NbN resonators demonstrate significantly better resilience. Moreover, NbN resonators exhibit an unexpected increase in QiQ_iQi​ at intermediate in-plane magnetic fields (B∥∼1B_{\parallel} \sim 1B∥​∼1 T), which we attribute to an enhanced frequency detuning that reduce coupling to two-level system defects. In contrast, grAl resonators show a distinct critical field above which QiQ_iQi​ rapidly decreases, strongly depending on resonator cross-section respect to the applied field direction. Characterization of the nonlinear properties at zero magnetic field reveals that the self-Kerr coefficient in grAl resonators is more than an order of magnitude higher than in NbN resonators, making grAl particularly attractive for applications requiring pronounced nonlinear interactions. Our findings illustrate a clear trade-off between the two materials: NbN offers superior magnetic-field resilience beneficial for hybrid circuit quantum electrodynamics applications, while grAl is more advantageous in low-field regimes demanding high impedance and strong nonlinearity.
We characterize niobium nitride (NbN) λ/2 coplanar waveguide resonators, which were fabricated from a 10-nm-thick film on silicon dioxide grown by sputter deposition. For films grown at 180 °C, we report a superconducting critical temperature of 7.4 K associated with a normal square resistance of 1 kΩ, leading to a kinetic inductance of 192 pH/◻. We fabricated resonators with a characteristic impedance up to 4.1 kΩ and internal quality factors Qi>104 in the single photon regime at zero magnetic field. Moreover, in the many photon regime, the resonators present a high magnetic field resilience with Qi>104 in a 6 T in-plane magnetic field and in a 300 mT out-of-plane magnetic field. These findings make such resonators a compelling choice for circuit quantum electrodynamics experiments involving quantum systems with small electric dipole moments operated in finite magnetic fields.
Superconducting thin films with high intrinsic kinetic inductance are of great importance for photon detectors, achieving strong coupling in hybrid systems, and protected qubits. We report on the performance of titanium nitride resonators, patterned on thin films (9–110 nm) grown by atomic layer deposition, with sheet inductances of up to 234 pH/□. For films thicker than 14 nm, quality factors measured in the quantum regime range from 0.2 to 1.0 × 106 and are likely limited by dielectric two-level systems. Additionally, we show characteristic impedances up to 28 kΩ, with no significant degradation of the internal quality factor as the impedance increases. These high impedances correspond to an increased single photon coupling strength of 24 times compared to a 50 Ω resonator, transformative for hybrid quantum systems and quantum sensing.
We have designed, fabricated, and tested a frequency-tunable high-Q superconducting resonator made from a niobium titanium nitride film. The frequency tunability is achieved by injecting a DC through a current-directing circuit into the nonlinear inductor whose kinetic inductance is current-dependent. We have demonstrated continuous tuning of the resonance frequency in a 180 MHz frequency range around 4.5 GHz while maintaining the high internal quality factor Qi > 180 000. This device may serve as a tunable filter and find applications in superconducting quantum computing and measurement. It also provides a useful tool to study the nonlinear response of a superconductor. In addition, it may be developed into techniques for measurement of the complex impedance of a superconductor at its transition temperature and for readout of transition-edge sensors.
Abstract Tantalum (Ta) has recently received considerable attention in manufacturing robust superconducting quantum circuits. Ta offers low microwave loss, high kinetic inductance compared to aluminium (Al) and niobium (Nb), and good compatibility with complementary metal-oxide-semiconductor (CMOS) technology, which is essential for quantum computing applications. Here we demonstrate the fabrication engineering of thickness-dependent high-quality-factor (high-  Qi\:{Q}_{i}Qi​ ) Ta superconducting microwave coplanar waveguide resonators. All films are deposited on high-resistivity silicon substrates at room temperature without additional substrate heating. Before Ta deposition, a niobium (Nb) seed layer is used to promote a body-centred cubic lattice (  α \:\alpha\:α -Ta) formation. We further engineer the kinetic inductance (  LK\:{L}_{K}LK​ ) of the resonators by varying Ta film thicknesses. High  LK\:{L}_{K}LK​ is a key advantage for applications because it facilitates the realisation of high-impedance, compact quantum circuits with enhanced coupling to qubits. The maximum internal quality factor  Qi\:{Q}_{i}Qi​ of  ∼ \:\sim\:∼ 3.6 × 10 6 in the high power regime and  Qi\:{Q}_{i}Qi​ of  ∼ \:\sim\:∼ 4.5 × 10 5 in the single-photon regime is achieved for 100 nm Ta which represents an improvement over previous room-temperature deposited Ta resonators on silicon substrates in the single photon regime, while the highest kinetic inductance of 0.6 pH/sq is obtained for the thinnest film, which is 40 nm. This combination of high  Qi\:{Q}_{i}Qi​ and high  LK\:{L}_{K}LK​ highlights the potential of Ta microwave circuits for high-fidelity operation of compact quantum circuits.