High power impulse magnetron sputtering of thin films for superconducting RF cavities S. Wilde 1,6 , R. Valizadeh 1 , O.B. Malyshev 1 , N. P. Barradas 2 , E. Alves 3,4 , G. B. G. Stenning 5 , A. Hannah 1 , S. Pattalwar 1 , B. Chesca 6 1 ASTeC, STFC Daresbury Laboratory, Warrington, UK. 2 C 2 TN, Centro de Ciȇncias Tecnológicas e Nucleares, Portugal. 3 IPFN, Instituto de Plasmas e Fusão Nuclear, Portugal. 4 Laboratório de Aceleradores e Tecnologias de Radiação, Portugal. 5 ISIS, STFC Rutherford Appleton Laboratory, Didcot, UK. 6 Department of Physics, Loughborough University, Loughborough, UK Abstract The production of superconducting coatings for radio frequency cavities is a rapidly developing field that should ultimately lead to acceleration gradients greater than those obtained by bulk Nb RF cavities. The use of thin films made from superconductors with > allows the possibility of multilayer superconductor – insulator – superconductor (SIS) films and also accelerators that could operate at temperatures above the 2 K typically used. SIS films theoretically allow increased acceleration gradient due to magnetic shielding of underlying superconducting layers [1] and higher operating temperature can reduce cost. High impulse magnetron sputtering (HiPIMS) and pulsed DC magnetron sputtering processes were used to deposit NbN and NbTiN thin films onto Si(100) substrate. The films were characterised using scanning electron microscopy (SEM), x-ray diffraction (XRD), Rutherford back-scattering spectroscopy (RBS) and a four point probe. Conclusions • NbN had T C of 16.1 K but was formed by columnar grains with voids and normal state resistivity of 835±260 μΩcm. • NbTiN had higher T C of 17.8 K and normal state resistivity of 45±7 μΩcm. [email protected] B PVD Deposition Facility 1 = 2 0 2 1.07 < Superconductor – Insulator – Superconductor (SIS) Multilayer Films • Upper superconducting layers with > and < allow increase in B C1 . • SIS films can provide magnetic shielding to the underlying superconducting layers. • Effect can theoretically allow larger accelerating gradients [1]. [1] A. Gurevich, Applied Physics Letters, 012511 (2006). NbN • NbN chosen for its T C of 17.3 K and of 2.9 nm. • Highest T C of 16.1 K • Normal state resistivity of 835±260 μΩcm NbTiN • NbN chosen for its T C of 18 K and of 3.8 nm. • Film has rough surface and columnar structure containing voids • at. % Nb = 47.5, at.% N = 42.6, at. % O = 9.9 • at. % Nb = 37.7, at.% Ti = 16.2, at. % N = 46.1 • Ideal ratio Nb = 33%, Ti = 17%, N=50% • Film appears to have smoother surface than NbN • Highest T C of 17.8 K • Normal state resistivity of 45±7 μΩcm
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High power impulse magnetron sputtering of thin films for superconducting RF cavities
S. Wilde1,6, R. Valizadeh1, O.B. Malyshev1, N. P. Barradas2 , E. Alves3,4, G. B. G. Stenning5, A. Hannah1, S. Pattalwar1, B. Chesca6
1 ASTeC, STFC Daresbury Laboratory, Warrington, UK. 2 C2TN, Centro de Ciȇncias Tecnológicas e Nucleares, Portugal. 3 IPFN, Instituto de Plasmas e Fusão Nuclear, Portugal. 4 Laboratório de Aceleradores e Tecnologias de Radiação, Portugal. 5 ISIS, STFC Rutherford Appleton Laboratory, Didcot, UK. 6 Department of Physics, Loughborough
University, Loughborough, UK
Abstract The production of superconducting coatings for radio frequency cavities is a rapidly developing field that should ultimately lead to acceleration gradients greater than those obtained by bulk Nb RF cavities. The use of thin films made from superconductors with𝑯𝑪 > 𝑯𝑪
𝑵𝒃allows the possibility of multilayer superconductor – insulator – superconductor (SIS) films and also accelerators that could operate at temperatures above the 2 K typically used. SIS films theoretically allow increased acceleration gradient due to magnetic shielding of underlying superconducting layers [1] and higher operating temperature can reduce cost. High impulse magnetron sputtering (HiPIMS) and pulsed DC magnetron sputtering processes were used to deposit NbN and NbTiN thin films onto Si(100) substrate. The films were characterised using scanning electron microscopy (SEM), x-ray diffraction (XRD), Rutherford back-scattering spectroscopy (RBS) and a four point probe.
Conclusions • NbN had TC of 16.1 K but was formed by
columnar grains with voids and normal state resistivity of 835±260 μΩcm.
• NbTiN had higher TC of 17.8 K and normal state resistivity of 45±7 μΩcm.
B
PVD Deposition Facility
𝐵𝐶1 =2𝜙0
𝜋𝑑2 𝑙𝑛𝑑
1.07𝜉 𝑑 < 𝜆
Superconductor – Insulator –Superconductor (SIS) Multilayer Films
• Upper superconducting layers with 𝑯𝑪 > 𝑯𝑪
𝑵𝒃 and 𝒅 < 𝝀 allow increase in BC1. • SIS films can provide magnetic shielding
to the underlying superconducting layers. • Effect can theoretically allow larger
accelerating gradients [1]. [1] A. Gurevich, Applied Physics Letters, 012511 (2006).
NbN • NbN chosen for its TC of 17.3 K
and 𝛏 of 2.9 nm.
• Highest TC of 16.1 K • Normal state resistivity of 835±260 μΩcm
NbTiN • NbN chosen for its TC of 18 K and 𝛏
of 3.8 nm.
• Film has rough surface and columnar structure containing voids
• at. % Nb = 47.5, at.% N = 42.6, at. % O = 9.9
• at. % Nb = 37.7, at.% Ti = 16.2, at. % N = 46.1
• Ideal ratio Nb = 33%, Ti = 17%, N=50%
• Film appears to have smoother surface than NbN
• Highest TC of 17.8 K • Normal state resistivity of 45±7 μΩcm
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