ON-AXIS DC SPUTTERED YBA2CU3O7-X FILMS UP TO 2-INCHES IN DIAMETER FORMICROWAVE ANTENNA-ARRAYS

We extended the planar on-axis DC sputtering process under high oxygen pressure (1-4 mbar) to the epitaxial growth of YBa2Cu3O7-x films on L aAlO3 substrates up to 2'' in diameter without scanning. The stability of the accordingly large plasma turned out to depend critically on th e homogeneity of the stoichiometric target and its bonding to the wate r-cooled sputtering cathode. The radiation-shielded heater plate provi ded temperature +/- 4K at 890 degrees C to the 2'' substrates. The qua lity of the large unpatterned films was controlled by inductive as wel l as by new microwave test sytems based on niobium choke-flange or sap phire-loaded cavities. These have been designed for highly sensitive s canning measurements of the surface resistance R(s) at 87 GHz and high power microwave tests at 20 GHz, respectively. Homogenenously low R(s ) values have been achieved on the large films up to surface fields of 5 mT at 77 K. A frequency. diplexer at 5 GHz for antenna arrays was d esigned with lumped elements and patterned from a 1'' film by means of photolithography, ion milling and wet etching. Its measured performan ce agrees well with numerical simulations.