Tantalum Nitride superconducting coplanar waveguide (CPW) resonators
ORAL
Abstract
Superconducting qubits and resonators made of tantalum have exhibited high
performance [1] due to low-loss natural oxides at the metal-air interface [2]. Recently,
we successfully realized thin-film growth of γ-Ta2N by molecular beam epitaxy on
c-plane sapphire substrates. 38 nm γ-Ta2N thin-films grown on c-plane sapphire
exhibited superconducting transition temperature of 0.48 K, a room temperature re-
sistivity of 75.5 μΩ·cm and RRR=2.6 [3]. CPW resonators in hanger mode with a 3-6-3
geometry were fabricated using the NIST 4-8 GHz design [4], targeting a coupling qual-
ity factor Qc ∼ 106, and characterized at 12 mK. The γ-Ta2N resonator exhibited a
power-independent Qi ∼ 1.5×104 and Qc ∼ 6×103, much lower than the target.
A 5 minute 10% HF treatment increased the Qi to ∼ 4×104 but reduced the Qc to
∼ 4.3×103. To understand the origin of the low Qi and Qc of these early γ-Ta2N
resonators, a control sample of a 130 nm thick Nb resonator on c-plane sapphire de-
posited by dc-sputtering was fabricated using the same mask. This control resonator
exhibited Qi ∼ 106 and 105 < Qc < 106 at 〈n〉 ∼ 104, confirming that the low Qc
of the early γ-Ta2N resonators is related to the material. The potential cause of the
low Qc, and comparison with other MBE-grown superconducting resonators will be
presented.
[1] Place et al., Nature Communications 12, 1779 (2021).
[2] Crowley et al., Physical Review X 13, 041005 (2023).
[3] Ithepalli et al., Applied Physics Letters 126, 222601 (2025).
[4] Kopas et al., arXiv:2204.07202 (2022).
performance [1] due to low-loss natural oxides at the metal-air interface [2]. Recently,
we successfully realized thin-film growth of γ-Ta2N by molecular beam epitaxy on
c-plane sapphire substrates. 38 nm γ-Ta2N thin-films grown on c-plane sapphire
exhibited superconducting transition temperature of 0.48 K, a room temperature re-
sistivity of 75.5 μΩ·cm and RRR=2.6 [3]. CPW resonators in hanger mode with a 3-6-3
geometry were fabricated using the NIST 4-8 GHz design [4], targeting a coupling qual-
ity factor Qc ∼ 106, and characterized at 12 mK. The γ-Ta2N resonator exhibited a
power-independent Qi ∼ 1.5×104 and Qc ∼ 6×103, much lower than the target.
A 5 minute 10% HF treatment increased the Qi to ∼ 4×104 but reduced the Qc to
∼ 4.3×103. To understand the origin of the low Qi and Qc of these early γ-Ta2N
resonators, a control sample of a 130 nm thick Nb resonator on c-plane sapphire de-
posited by dc-sputtering was fabricated using the same mask. This control resonator
exhibited Qi ∼ 106 and 105 < Qc < 106 at 〈n〉 ∼ 104, confirming that the low Qc
of the early γ-Ta2N resonators is related to the material. The potential cause of the
low Qc, and comparison with other MBE-grown superconducting resonators will be
presented.
[1] Place et al., Nature Communications 12, 1779 (2021).
[2] Crowley et al., Physical Review X 13, 041005 (2023).
[3] Ithepalli et al., Applied Physics Letters 126, 222601 (2025).
[4] Kopas et al., arXiv:2204.07202 (2022).
*This work was supported by the AFOSR/LPS programMaterials for Quantum Computation (MQC) as part of the EpiQteam monitored by Dr. Ali Sayir of AFOSR and Dr. Erin Clevelandof LPS, and partially by an ONR Grant No. N00014-22-1-2633monitored by Dr. Paul Maki. This material is based upon worksupported by the Air Force Office of Scientific Research underAward No. FA9550-23-1-0688. This work was performed in part at theCornell NanoScale Facility, a member of the NationalNanotechnology Coordinated Infrastructure (NNCI), which issupported by the National Science Foundation (Grant No. NNCI-2025233).
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Presenters
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Amit Rohan Rajapurohita
- Cornell University