ON-AXIS DC SPUTTERED YBA2CU3O7-X FILMS UP TO 2-INCHES IN DIAMETER FOR MICROWAVE 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 LaAlO3 substrates up to 2'' in diameter without scanning. The stability of the accordingly large plasma turned out to depend critically on the homogeneity of the stoichiometric target and its bonding to the water-cooled sputtering cathode. The radiation-shielded heater plate provided temperature +/- 4K at 890 degrees C to the 2'' substrates. The quality of the large unpatterned films was controlled by inductive as well as by new microwave test sytems based on niobium choke-flange or sapphire-loaded cavities. These have been designed for highly sensitive scanning 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 designed with lumped elements and patterned from a 1'' film by means of photolithography, ion milling and wet etching. Its measured performance agrees well with numerical simulations.