Speaker
Description
"For the last few decades, the material of choice for SRF cavities has been bulk niobium. RF performance of bulk $Nb$ cavity has already approached its theoretical limit. To enhance RF cavity performance and cost-efficiency, research has shifted towards the use of other alternative higher $T_c$ materials, such as $NbN$, $NbTiN$, $MgB_2$, etc. However, the use of alternative superconducting materials, despite their higher $T_c$, may not allow high accelerating gradients and quality factors greater than $Nb$ due to their smaller $H_{c1}$. Addressing this problem, Alex Gurevich in 2006 proposed a theory involving superconductor-insulator-superconductor (SIS) structures to shield an underlying superconductor from the applied magnetic fields, thus increasing the maximum accelerating gradient beyond the bulk $Nb$ limits.
$NbTiN$ is one of the most promising alternative materials to $Nb$, which already displayed high-quality factors in coated cavities for research. The present work focuses on the deposition of high $T_c$ (17.3 K) $NbTiN$ thin films, primarily due to their high $T_c$ and they also encompass all the benefits of $NbN$ while displaying superior metallic conduction characteristics with higher titanium content. We used the industrial coating machine, CC800, to deposit single layers of $NbTiN$ thin films onto silicon ($Si$), a thick film of $Nb$, and aluminium nitride ($AlN$) substrates using DCMS and HiPIMS techniques. The primary focus here is solely on optimizing $NbTiN$ thin films for potential future use in SIS structures. The impact of various deposition parameters on the microstructure, phase formation, and subsequent superconducting properties of $NbTiN$ films deposited on various substrates are presented. The results indicate that HiPIMS yields films characterized by higher density and fewer voids in comparison to DCMS. Following the successful optimization of $NbTiN$ thin films, they will be utilized for the development of SIS structures."
