Physical vapour deposition of NbTiN thin films for superconducting RF cavities.

The production of superconducting coatings for radio frequency (RF) 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 thermodynamic critical field, Hc > HC(Nb), allows the possibility of multilayer superconductor – insulator – superconductor (SIS) films and accelerators that could operate at temperatures above 2 K. SIS films theoretically allow increased acceleration gradient due to magnetic shielding of underlying superconducting layers [1] and higher operating temperature can reduce cost [2]. High impulse magnetron sputtering (HiPIMS) and pulsed DC magnetron sputtering processes were used to deposit 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.