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LAL-Orsay is developing an important effort on R&D and technology studies on RF power couplers for superconductive cavities. These are complex and high technology devices due to their basic functions: RF power matching between source and cavity, vacuum and temperature separation from the environment to the cavity. One of the most critical components of high power couplers is the RF ceramic window that allows the power flux to be injected in the coaxial line. The presence of a dielectric window on an RF power line has in fact a strong influence on the multipactor phenomena, a resonant electron discharge that is strongly limiting for the RF components performances. The most important method to reduce the multipactor is to decrease the secondary emission yield of the ceramic window. Due to its low secondary electron emission coefficient, TiN thin film is used as a multipactor suppressor coating on ceramic coupler windows. In addition, TiN permits to drain away electric charges on the surfaces to avoid material break down.
In this framework, a sputtering machine was developed allowing thin layer titanium nitride coating on ceramic. The coupler operating conditions, the physical properties of TiN layer and alumina substrate in addition to windows geometries have defined the strict constraints that have been taken into account in the definition of the coating bench design. In this study, a full description of sputtering machine will be given.
By maintaining a constant bias and a fixed ionisation gas flow, an optimisation of reactive gas flow will be necessary for stoichiometric deposit obtaining. Once these parameters determined, a study of deposition rate variation for different process pressure value will be done. The influence of substrate to target distance on deposit stoichiometry and thickness will be also presented.
As TiN deposit thickness is a very important parameter to control, a correlation between quartz crystal microbalance given value and the real deposition thickness is determined for a better in-situ monitoring.