On-axis DC sputtered YBa/sub 2/Cu/sub 3/O/sub 7/(-x) films up to 2" in diameter for microwave antenna arrays

We have extended the planar on-axis DC sputtering process under high oxygen pressure (1-4 mbar) to the epitaxial growth of YBa/sub 2/Cu/sub 3/O/sub 7-x/ films on LaAlO/sub 3/ 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 uniformity of /spl plusmn/4K at 890/spl deg/C to the 2" substrates. The quality of the large unpatterned films was controlled by inductive as well as by new microwave test systems based on niobium choke-flange or sapphire-loaded cavities. These have been designed for highly sensitive scanning measurements of the surface resistance R/sub s/ at 87 GHz and high power microwave tests at 20 GHz, respectively. Homogeneous low R/sub 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. >