Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2403.00723 · APL Quantum

Characterization of process-related interfacial dielectric loss in aluminum-on-silicon by resonator microwave measurements, materials analysis, and imaging

Lert Chayanun, Janka Biznárová, Lunjie J. Zeng, Per Malmberg, Andreas Nylander, Amr Osman, Marcus Rommel, Pui Lam Tam, Eva Olsson, Per Delsing, August Yurgens, Jonas Bylander, Anita Fadavi Roudsari

Published Jun 1, 2024• 13 citations
arXivHTMLPDF

Abstract

We systematically investigate the influence of the fabrication process on dielectric loss in aluminum-on-silicon superconducting coplanar waveguide resonators with internal quality factors (Qi) of about one million at the single-photon level. These devices are essential components in superconducting quantum processors; they also serve as proxies for understanding the energy loss of superconducting qubits. By systematically varying several fabrication steps, we identify the relative importance of reducing loss at the substrate–metal and substrate–air interfaces. We find that it is essential to clean the silicon substrate in hydrogen fluoride (HF) prior to aluminum deposition. A post-fabrication removal of the oxides on the surface of the silicon substrate and the aluminum film by immersion in HF further improves the Qi. We observe a small, but noticeable, adverse effect on the loss by omitting either standard cleaning (SC1), pre-deposition heating of the substrate to 300 °C, or in situ post-deposition oxidation of the film’s top surface. We find no improvement due to excessive pumping meant to reach a background pressure below 6 × 10−8 mbar. We correlate the measured loss with microscopic properties of the substrate–metal interface through characterization with x-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, transmission electron microscopy, energy-dispersive x-ray spectroscopy, and atomic force microscopy.

DOI
10.1063/5.0208140

Related papers

Substrate surface engineering for high-quality silicon/aluminum superconducting resonators

C T Earnest, J. H. Béjanin, T G McConkey +4 more

Abstract Quantum bits (qubits) with long coherence times are an important element for the implementation of medium- and large-scale quantum computers. In the case of superconducting planar qubits, understanding and improving qubits’ quality can be achieved by studying superconducting planar resonators. In this paper, we fabricate and characterize coplanar waveguide resonators made from aluminum thin films deposited on silicon substrates. We perform three different substrate surface treatments prior to aluminum deposition: one chemical treatment based on a hydrofluoric acid clean; one physical treatment consisting of a thermal annealing at 880 °C in high vacuum; and one combined treatment comprising both the chemical and the physical treatments. The aim of these treatments is to remove the two-level state (TLS) defects hosted by the native oxides residing at the various samples’ interfaces. We first characterize the fabricated samples through cross-sectional tunneling electron microscopy, acquiring electron energy loss spectroscopy maps of the samples’ cross sections. These measurements show that both the chemical and the physical treatments almost entirely remove native silicon oxide from the substrate surface and that their combination results in the cleanest interface. Additionally, we analyze the effects of the various substrate treatments on the roughness of the silicon surface by means of atomic force microscopy surface morphology mapping. We then study the quality of the resonators by means of microwave measurements in the ‘quantum regime’, i.e., at a temperature T ∼ 10 mK and at a mean microwave photon number 〈 n ph 〉 ∼ 1 . In this regime, we find that both surface treatments independently improve the resonator’s intrinsic quality factor by ≈172%. The highest quality factor is obtained for the combined treatment, Q i ≈ 0.82 million, corresponding to an improvement by ≈256%. Finally, we find that the TLS quality factor averaged over a time period of 3 h is ∼3 million at 〈 n ph 〉 ∼ 10 , indicating that substrate surface engineering can potentially reduce the TLS loss below other losses such as quasiparticle loss and flux noise.

arXiv:1807.08072•Superconductor Science and Technology•Oct 1, 2018•73 citations

Mitigation of interfacial dielectric loss in aluminum-on-silicon superconducting qubits

Janka Biznárová, Amr Osman, Emil Rehnman +9 more

Abstract We demonstrate aluminum-on-silicon planar transmon qubits with time-averaged T 1 energy relaxation times of up to 270 μs, corresponding to Q = 5 million, and a highest observed value of 501 μs. Through materials analysis techniques and numerical simulations we investigate the dominant source of energy loss, and devise and demonstrate a strategy toward its mitigation. Growing aluminum films thicker than 300 nm reduces the presence of oxide, a known host of defects, near the substrate-metal interface, as confirmed by time-of-flight secondary ion mass spectrometry. A loss analysis of coplanar waveguide resonators shows that this results in a reduction of dielectric loss due to two-level system defects. The correlation between the enhanced performance of our devices and the film thickness is due to the aluminum growth in columnar structures of parallel grain boundaries: transmission electron microscopy shows larger grains in the thicker film, and consequently fewer grain boundaries containing oxide near the substrate-metal interface.

arXiv:2310.06797•npj Quantum Information•Aug 14, 2024•41 citations

Fabrication artifacts and parallel loss channels in metamorphic epitaxial aluminum superconducting resonators

Christopher J. K. Richardson, Nathan Paul Siwak, Justin C. Hackley +5 more

Abstract Fabrication of coplanar waveguide resonators with internal quality factors near 10 6 remains challenging. Here, high-purity superconductors are implemented through metamorphic epitaxial aluminum that is grown via molecular beam epitaxy on silicon and sapphire substrates. X-ray diffraction and scanning transmission electron microscopy indicate an abrupt highly ordered interface that results in crystal relaxation within a few monolayers of the substrate interface and no measurable interfacial contamination. Quarter-wave coplanar waveguide resonators are fabricated using optical lithography and measured at temperatures below 100 mK. Post measurement characterization with charge contrast imaging in a scanning electron microscope identifies processing artifacts at the waveguide sidewalls, on the exposed substrate area and on the exposed aluminum surface. Of primary importance are processing induced corrosion defects on aluminum sidewalls, nanoparticle contamination, and photoresist residue that is difficult to remove without affecting the superconductor material. Likely correlations between these artifacts and the measured quality factor are discussed in context of device to device variations in resonator performance.

Superconductor Science and Technology•Apr 15, 2016•46 citations

Thin film metrology and microwave loss characterization of indium and aluminum/indium superconducting planar resonators

Corey Rae McRae, J. H. Béjanin, C. T. Earnest +6 more

Scalable architectures characterized by quantum bits (qubits) with low error rates are essential to the development of a practical quantum computer. In the superconducting quantum computing implementation, understanding and minimizing material losses are crucial to the improvement of qubit performance. A new material that has recently received particular attention is indium, a low-temperature superconductor that can be used to bond pairs of chips containing standard aluminum-based qubit circuitry. In this work, we characterize microwave loss in indium and aluminum/indium thin films on silicon substrates by measuring superconducting coplanar waveguide resonators and estimating the main loss parameters at powers down to the sub-photon regime and at temperatures between 10 and 450 mK. We compare films deposited by thermal evaporation, sputtering, and molecular beam epitaxy. We study the effects of heating in a vacuum and ambient atmospheric pressure as well as the effects of pre-deposition wafer cleaning using hydrofluoric acid. The microwave measurements are supported by thin film metrology including secondary-ion mass spectrometry. For thermally evaporated and sputtered films, we find that two-level state are the dominant loss mechanism at low photon number and temperature, with a loss tangent due to native indium oxide of ∼5×10−5. The molecular beam epitaxial films show evidence of the formation of a substantial indium-silicon eutectic layer, which leads to a drastic degradation in resonator performance.

arXiv:1712.08706•Journal of Applied Physics•May 24, 2018•13 citations

Low loss superconducting resonators enabled by aluminum microstructural engineering and dielectric trimming

Mahmoud Almansouri, Umar T. F. Alhuwaymel, Ibraheem AlYousef +5 more

Material losses in superconducting circuits fundamentally limit qubit coherence times and resonator quality factors. Most research efforts focus on mitigating losses at circuit interfaces, including metal--substrate, substrate--air, and metal--air interfaces. However, the correlation between TLS and non-TLS losses with the intrinsic properties of the superconducting metal and the dielectric edge smoothness is not well studied. In this work, we link the aluminum film grain size to non-TLS losses and the dielectric trimming profile and roughness to TLS loss; both loss mechanisms are subsequently mitigated. To reduce metal-related losses, we engineer the aluminum microstructure by heating during deposition, increasing grain size and reducing grain boundary density. Beyond mitigating metal losses, we introduce a two-step etching technique, Tropic etching, to suppress dielectric TLS loss by producing an ultra-smooth silicon surface with minimal defects and redeposition. These results lay out the fabrication pathway for aluminum resonators with lower loss, demonstrating two-orders-of-magnitude improvement in quality factor from $6\times10^{4}$ to $2.3\times10^{6}$. Since aluminum is the basis for most high-coherence Josephson junctions and dielectric edges are inherent to all common device geometries, the improvements in aluminum microstructure and edge profiling, presented here, can enhance the performance of superconducting quantum devices.

quant-pharXiv:2607.22265•Jul 27, 2026•0 citations

Comparison of dielectric loss in titanium nitride and aluminum superconducting resonators

Alexander J. Melville, Greg Calusine, Wayne H. Woods +8 more

Lossy dielectrics are a significant source of decoherence in superconducting quantum circuits. In this report, we model and compare the dielectric loss in bulk and interfacial dielectrics in titanium nitride (TiN) and aluminum (Al) superconducting coplanar waveguide resonators. We fabricate isotropically trenched resonators to produce a series of device geometries that accentuate a specific dielectric region's contribution to the resonator quality factor. While each dielectric region contributes significantly to loss in TiN devices, the metal–air interface dominates the loss in the Al devices. Furthermore, we evaluate the quality factor of each TiN resonator geometry with and without a post-process hydrofluoric etch and find that it reduced losses from the substrate–air interface, thereby improving the quality factor.

arXiv:2007.07338•Applied Physics Letters•Sep 21, 2020•69 citations
We systematically investigate the influence of the fabrication process on dielectric loss in aluminum-on-silicon superconducting coplanar waveguide resonators with internal quality factors (Qi) of about one million at the single-photon level. These devices are essential components in superconducting quantum processors; they also serve as proxies for understanding the energy loss of superconducting qubits. By systematically varying several fabrication steps, we identify the relative importance of reducing loss at the substrate–metal and substrate–air interfaces. We find that it is essential to clean the silicon substrate in hydrogen fluoride (HF) prior to aluminum deposition. A post-fabrication removal of the oxides on the surface of the silicon substrate and the aluminum film by immersion in HF further improves the Qi. We observe a small, but noticeable, adverse effect on the loss by omitting either standard cleaning (SC1), pre-deposition heating of the substrate to 300 °C, or in situ post-deposition oxidation of the film’s top surface. We find no improvement due to excessive pumping meant to reach a background pressure below 6 × 10−8 mbar. We correlate the measured loss with microscopic properties of the substrate–metal interface through characterization with x-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, transmission electron microscopy, energy-dispersive x-ray spectroscopy, and atomic force microscopy.
Abstract Quantum bits (qubits) with long coherence times are an important element for the implementation of medium- and large-scale quantum computers. In the case of superconducting planar qubits, understanding and improving qubits’ quality can be achieved by studying superconducting planar resonators. In this paper, we fabricate and characterize coplanar waveguide resonators made from aluminum thin films deposited on silicon substrates. We perform three different substrate surface treatments prior to aluminum deposition: one chemical treatment based on a hydrofluoric acid clean; one physical treatment consisting of a thermal annealing at 880 °C in high vacuum; and one combined treatment comprising both the chemical and the physical treatments. The aim of these treatments is to remove the two-level state (TLS) defects hosted by the native oxides residing at the various samples’ interfaces. We first characterize the fabricated samples through cross-sectional tunneling electron microscopy, acquiring electron energy loss spectroscopy maps of the samples’ cross sections. These measurements show that both the chemical and the physical treatments almost entirely remove native silicon oxide from the substrate surface and that their combination results in the cleanest interface. Additionally, we analyze the effects of the various substrate treatments on the roughness of the silicon surface by means of atomic force microscopy surface morphology mapping. We then study the quality of the resonators by means of microwave measurements in the ‘quantum regime’, i.e., at a temperature T ∼ 10 mK and at a mean microwave photon number 〈 n ph 〉 ∼ 1 . In this regime, we find that both surface treatments independently improve the resonator’s intrinsic quality factor by ≈172%. The highest quality factor is obtained for the combined treatment, Q i ≈ 0.82 million, corresponding to an improvement by ≈256%. Finally, we find that the TLS quality factor averaged over a time period of 3 h is ∼3 million at 〈 n ph 〉 ∼ 10 , indicating that substrate surface engineering can potentially reduce the TLS loss below other losses such as quasiparticle loss and flux noise.
Abstract We demonstrate aluminum-on-silicon planar transmon qubits with time-averaged T 1 energy relaxation times of up to 270 μs, corresponding to Q = 5 million, and a highest observed value of 501 μs. Through materials analysis techniques and numerical simulations we investigate the dominant source of energy loss, and devise and demonstrate a strategy toward its mitigation. Growing aluminum films thicker than 300 nm reduces the presence of oxide, a known host of defects, near the substrate-metal interface, as confirmed by time-of-flight secondary ion mass spectrometry. A loss analysis of coplanar waveguide resonators shows that this results in a reduction of dielectric loss due to two-level system defects. The correlation between the enhanced performance of our devices and the film thickness is due to the aluminum growth in columnar structures of parallel grain boundaries: transmission electron microscopy shows larger grains in the thicker film, and consequently fewer grain boundaries containing oxide near the substrate-metal interface.
Abstract Fabrication of coplanar waveguide resonators with internal quality factors near 10 6 remains challenging. Here, high-purity superconductors are implemented through metamorphic epitaxial aluminum that is grown via molecular beam epitaxy on silicon and sapphire substrates. X-ray diffraction and scanning transmission electron microscopy indicate an abrupt highly ordered interface that results in crystal relaxation within a few monolayers of the substrate interface and no measurable interfacial contamination. Quarter-wave coplanar waveguide resonators are fabricated using optical lithography and measured at temperatures below 100 mK. Post measurement characterization with charge contrast imaging in a scanning electron microscope identifies processing artifacts at the waveguide sidewalls, on the exposed substrate area and on the exposed aluminum surface. Of primary importance are processing induced corrosion defects on aluminum sidewalls, nanoparticle contamination, and photoresist residue that is difficult to remove without affecting the superconductor material. Likely correlations between these artifacts and the measured quality factor are discussed in context of device to device variations in resonator performance.
Scalable architectures characterized by quantum bits (qubits) with low error rates are essential to the development of a practical quantum computer. In the superconducting quantum computing implementation, understanding and minimizing material losses are crucial to the improvement of qubit performance. A new material that has recently received particular attention is indium, a low-temperature superconductor that can be used to bond pairs of chips containing standard aluminum-based qubit circuitry. In this work, we characterize microwave loss in indium and aluminum/indium thin films on silicon substrates by measuring superconducting coplanar waveguide resonators and estimating the main loss parameters at powers down to the sub-photon regime and at temperatures between 10 and 450 mK. We compare films deposited by thermal evaporation, sputtering, and molecular beam epitaxy. We study the effects of heating in a vacuum and ambient atmospheric pressure as well as the effects of pre-deposition wafer cleaning using hydrofluoric acid. The microwave measurements are supported by thin film metrology including secondary-ion mass spectrometry. For thermally evaporated and sputtered films, we find that two-level state are the dominant loss mechanism at low photon number and temperature, with a loss tangent due to native indium oxide of ∼5×10−5. The molecular beam epitaxial films show evidence of the formation of a substantial indium-silicon eutectic layer, which leads to a drastic degradation in resonator performance.
Material losses in superconducting circuits fundamentally limit qubit coherence times and resonator quality factors. Most research efforts focus on mitigating losses at circuit interfaces, including metal--substrate, substrate--air, and metal--air interfaces. However, the correlation between TLS and non-TLS losses with the intrinsic properties of the superconducting metal and the dielectric edge smoothness is not well studied. In this work, we link the aluminum film grain size to non-TLS losses and the dielectric trimming profile and roughness to TLS loss; both loss mechanisms are subsequently mitigated. To reduce metal-related losses, we engineer the aluminum microstructure by heating during deposition, increasing grain size and reducing grain boundary density. Beyond mitigating metal losses, we introduce a two-step etching technique, Tropic etching, to suppress dielectric TLS loss by producing an ultra-smooth silicon surface with minimal defects and redeposition. These results lay out the fabrication pathway for aluminum resonators with lower loss, demonstrating two-orders-of-magnitude improvement in quality factor from 6×1046\times10^{4}6×104 to 2.3×1062.3\times10^{6}2.3×106. Since aluminum is the basis for most high-coherence Josephson junctions and dielectric edges are inherent to all common device geometries, the improvements in aluminum microstructure and edge profiling, presented here, can enhance the performance of superconducting quantum devices.
Lossy dielectrics are a significant source of decoherence in superconducting quantum circuits. In this report, we model and compare the dielectric loss in bulk and interfacial dielectrics in titanium nitride (TiN) and aluminum (Al) superconducting coplanar waveguide resonators. We fabricate isotropically trenched resonators to produce a series of device geometries that accentuate a specific dielectric region's contribution to the resonator quality factor. While each dielectric region contributes significantly to loss in TiN devices, the metal–air interface dominates the loss in the Al devices. Furthermore, we evaluate the quality factor of each TiN resonator geometry with and without a post-process hydrofluoric etch and find that it reduced losses from the substrate–air interface, thereby improving the quality factor.