Tantalum Nitride superconducting coplanar waveguide (CPW) resonators
Oral-In-person
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).
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Presenters
-
Amit Rohan Rajapurohita
- Cornell University