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arXiv:2606.10719

Ultra-high Q-factor superconducting tantalum resonators on 300 mm Si wafers

R. Acharya, D. Perez Lozano, Ts. Ivanov, S. Massar, C. Vrancken, Y. Canvel, Y. Li, A. M. Vadiraj, J. Van Damme, S. Aghaeimeibodi, A. Khalajhedayati, M. Mongillo, O. Painter, D. Wan, A. Potočnik, K. De Greve

quant-phSubmitted Jun 9, 2026• Announced Jun 10, 2026• 1 citation
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Abstract

Superconducting resonators are central to superconducting quantum information technologies and essential for bosonic qubit architectures, where long-lived storage modes enable hardware-efficient error correction. Achieving ultra-high quality factors in scalable planar circuits is challenging because multiple dissipation channels contribute to the total loss. Here we report planar $α$-Ta resonators fabricated on 300 mm ultra-high-resistivity ($>10$ k$Ω$ cm) intrinsic silicon using industrial processes, achieving median internal Q factors exceeding 40 million and maxima above 60 million. Energy-participation-ratio analysis identifies a dominant participation-controlled interface loss mechanism and places conservative upper bounds on substrate-associated dissipation. For the best-performing substrate, the inferred substrate loss tangent is below $1.0 \times 10^{-8}$, establishing industrial MCZ silicon among the lowest-loss substrate platforms reported for superconducting resonators. At the same time, the exceptionally low losses show no clear correlation with commonly cited silicon substrate metrics such as room-temperature resistivity or impurity concentrations. More broadly, these studies establish industrial 300 mm processing, careful interface engineering, and 300 mm MCZ silicon substrates as a promising platform for resonator-heavy superconducting quantum architectures with ultra-high quality factors.

Comments
main text: 11 pages, 4 figures; extended and supplementary: 12 figures and 4 tables

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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.
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-Q_i) 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 ensure a body-centred cubic lattice (α-Ta) formation. We further engineer the kinetic inductance (L_K) resonators by varying Ta film thicknesses. High L_K 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 Q_i of ~ 3.6 * 10^6 is achieved at the high power regime for 100 nm Ta, while the highest kinetic inductance is obtained to be 0.6 pH/sq for the thinnest film, which is 40 nm. This combination of high Q_i and high L_K highlights the potential of Ta microwave circuits for high-fidelity operations of compact quantum circuits.
Superconducting coplanar waveguide resonators are essential components in quantum processors, where their internal quality factor (Qi) constrains qubit coherence and readout fidelity. In niobium devices, microwave losses at millikelvin temperatures are strongly influenced by two-level systems (TLS) associated with the complex NbOx surface oxide. To mitigate these losses, we investigate a surface-engineering approach in which Nb films are capped in situ with a thin tantalum layer to suppress Nb2O5 formation and replace the native NbOx interface with a Ta-based oxide. We fabricate Nb/Ta bilayer and reference Nb resonators on high-resistivity silicon using identical DC sputtering and wet etching conditions, and characterize their performance at millikelvin temperatures. Fresh Ta-encapsulated devices exhibit internal quality factors up to 2.4 x 10^6 in the near-single-photon regime, with power dependence consistent with reduced TLS-related loss at the metal-air interface. A control Nb device fabricated under the same process shows comparatively lower Q_TLS, consistent with the beneficial effect of the Ta capping layer. Furthermore, ageing tests performed on Nb/Ta resonators after six months reveal a moderate reduction in Q_TLS relative to their initial values, yet the performance remains superior to newly fabricated Nb-only devices. These results suggest that thin Ta encapsulation enhances interface quality and contributes to improved temporal stability while remaining compatible with Nb-based fabrication workflows.