Superconducting, structural and surface properties of GdBaCuO thin films deposited by electron cyclotron resonance supported sputtering

Thin films of GdBaCuO have been deposited in off-axis geometry by electron cyclotron resonance (ECR) supported DC sputtering at 2.45 GHz in an oxygen-argon mixture at a total pressure of 10−1 mbar. Using this technique the target voltage could be varied over a wide range from −40 to −200 V without influencing the plasma generation. The deposition characteristics of the sputtering device were investigated in detail for GdBa2Cu3O7 and pure Cu targets. The superconducting and structural properties of the films and their surface morphologies were determined as a function of substrate temperature, composition, total pressure and target voltage. Optimum preparation conditions were low target voltages between −40 and −75 V, an oxygen partial pressure ranging from 10−4 to 3 × 10−4 mbar and a copper content slightly above stoichiometry. At these conditions the films grew with pure c-axis orientation at comparably low substrate temperatures between 650C and 680C. They showed superconducting transition temperatures between 91 K and 92 K, critical current densities of 4 × 106 A/cm2 (77 K, zero field), surface resistances of 1.9 Mω at 18.75 GHz and 77 K, and an average surface roughness of 2.5 nm. 0 1997 Elsevier Science B.V