Manufacturing of radiofrequency cavities by deposition of superconducting thin films has never emerged as an alternative method to the niobium bulk technology because of the poor performances of accelerating fields (Eacc) achieved. Nevertheless this established fact could be soon in balance again because of the necessity to use any superconductor else than Nb to overcome actual fundamental limitations.
Historically R & D studies have been much more intensive on bulk Nb cavities and performances increased steadily by decisive findings in appropriate chemical, thermal and surface treatments. The purpose of this paper is to give a review of these experimental advances and theoretical explanations to attempt to understand limited performances of thin film cavities and cast a new light on this issue.
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