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Applied Physics Letters

Microwave losses in MgO, LaAlO3, and (La0.3Sr0.7)(Al0.65Ta0.35)O3 dielectrics at low power and in the millikelvin temperature range

M. Arzeo, Floriana Lombardi, Thilo Bauch

Published May 26, 2014• 15 citations
Publisher

Abstract

We have investigated both the temperature and the power dependence of microwave losses for various dielectrics commonly used as substrates for the growth of high critical temperature superconductor thin films. We present measurement of niobium superconducting λ∕2 coplanar waveguide resonators, fabricated on MgO, LaAlO3, and (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT), at the millikelvin temperature range and at low input power. By comparing our results with the two-level system model, we have discriminated among different dominant loss mechanisms. LSAT has shown the best results as regards the dielectric losses in the investigated regimes.

DOI
10.1063/1.4880357

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We have investigated both the temperature and the power dependence of microwave losses for various dielectrics commonly used as substrates for the growth of high critical temperature superconductor thin films. We present measurement of niobium superconducting λ∕2 coplanar waveguide resonators, fabricated on MgO, LaAlO3, and (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT), at the millikelvin temperature range and at low input power. By comparing our results with the two-level system model, we have discriminated among different dominant loss mechanisms. LSAT has shown the best results as regards the dielectric losses in the investigated regimes.
We have investigated both the temperature and the power dependence of microwave losses for various dielectrics commonly used as substrates for the growth of High critical Temperature Superconductor thin films. We present measurement of niobium superconducting λ/2λ/2λ/2 coplanar waveguide resonators, fabricated on La0.3Sr0.7Al0.65Ta0.35O3La_{0.3}Sr_{0.7}Al_{0.65}Ta_{0.35}O_3La0.3​Sr0.7​Al0.65​Ta0.35​O3​ (LSAT), MgOMgOMgO (MgO) and LaAlO3LaAlO_3LaAlO3​ (LAO), at the millikelvin temperature range and at low input power. By comparing our results with the Two-Level System (TLS) model, we have discriminated among different dominant loss mechanisms. LSAT has shown the best results as regards the dielectric losses in the investigated regimes.
We have investigated the temperature dependence of microwave losses in the low-power limit and millikelvin temperature range of a thin-film YBa2Cu3O7-x(YBCO) λ/2 coplanar waveguide resonator patterned on a (La0.3Sr0.7) (Al0.65Ta0.35)O3(LSAT) substrate covered by a CeO2seed layer. The unloaded quality factor is mainly governed by the surface resistance of the YBCO film and the dielectric losses caused by resonant absorption due to a bath of two-level fluctuators in the dielectrics. The value of the unloaded quality factor at 20 mK and low power, i.e., Q0≃2000, allows for the realization of YBCO microwave quantum circuits implementing biepitaxial grain-boundary Josephson junctions.
Materials that feature very high permittivity and very low losses at low temperatures offer interesting opportunities for improving the performance of a variety of microwave-optical devices such as phase shifters and quantum transducers. In this Letter, superconducting Al coplanar waveguide resonators between 4 and 6 GHz were used to determine the complex permittivity and loss of thin film SrTiO3 on Si at cryogenic temperatures. We report a permittivity of 1950 ± 140 and a high-power loss tangent (tan δSTO) of 3.4 ± 0.1×10−4 at millikelvin temperatures. To further investigate the potential of SrTiO3 for use in emerging quantum technology applications, the transition of tan δSTO into the single photon regime was analyzed. Our findings reveal a loss scaling that aligns closely with a two-level system loss mechanism. We observe a nearly two orders of magnitude difference in tan δSTO between high and low input power levels, consistent with that two-level system loss picture.
We investigated the loss mechanisms of superconducting circuits with epitaxially grown NbN(100) on MgO(100) substrates by measuring quarter-wave coplanar waveguide resonators with various strip and slot widths. The power dependence of the internal quality factor and the temperature dependence of the resonance frequency shift were evaluated in a dilution refrigerator. The measurement and analysis of the loss in these resonators indicate that the loss was dominated by a two-level system (TLS) loss and the TLS host materials were primarily distributed at the surface of the substrate.
Abstract The performance of superconducting microwave circuits is strongly influenced by the material properties of the superconducting film and substrate. While progress has been made in understanding the importance of surface preparation and the effect of surface oxides, the complex effect of superconductor film structure on microwave losses is not yet fully understood. In this study, we investigate the microwave properties of niobium resonators with different crystalline properties and related surface topographies. We analyze a series of magnetron sputtered films in which the Nb crystal orientation and surface topography are changed by varying the substrate temperatures between room temperature and 975 K. The lowest-loss resonators that we measure have quality factors of over 10 6 at single-photon powers, among the best ever recorded using the Nb on sapphire platform. We observe the highest quality factors in films grown at an intermediate temperature regime of the growth series (550 K) where the films display both preferential ordering of the crystal domains and low surface roughness. Furthermore, we analyze the temperature-dependent behavior of our resonators to learn about how the quasiparticle density in the Nb film is affected by the niobium crystal structure and the presence of grain boundaries. Our results stress the connection between the crystal structure of superconducting films and the loss mechanisms suffered by the resonators and indicate that even a moderate change in temperature during thin film deposition can significantly affect the resulting quality factors.
We report on the characterization of microwave loss of thin aluminum oxide films at low temperatures using superconducting lumped resonators. The oxide films are fabricated using plasma oxidation of aluminum and have a thickness of 5 nm. We measure the dielectric loss versus microwave power for resonators with frequencies in the GHz range at temperatures from 54 to 303 mK. The power and temperature dependence of the loss are consistent with the tunneling two-level system theory. These results are relevant to understanding decoherence in superconducting quantum devices. The obtained oxide films are thin and robust, making them suitable for capacitors in compact microwave resonators.