Effect of deposition conditions and substrate position on the properties of superconducting YBa 2Cu 3O δ thin films prepared in a facing-target sputtering system

Abstract

Superconducting YBa 2Cu 8 O δ thin films were grown using a facing-target sputtering technique with a special substrate holder designed to produce a high oxygen partial pressure around the growing film. There existed a complementary effect of discharge gas pressure, power and substrate position for optimizing the deposition conditions. For the pressure range of 9–200 m Torr, a high transition temperature (T c) could be obtained at a given pressure by choice of substrate position. At low deposition pressure the substrate needed to be away from the plasma because of the resputtering effect from energetic O − ions, while at high pressure the substrate was close to the plasma as gas scattering reduced their effect. High quality films with a c-axis oriented epitaxial structure and lattice constant c o of 1.170–1.172 nm of stoichiometric composition, and smooth morphology were grown on (100) MgO in the pressure range of 70–90 m Torr. The as-deposited films had a relative resistance R(300K)⧹R(100K) of about 3, a transition temperature T c of 88 K, and transition width of about 2 k.