Role of hydrogen in the growth of Y1Ba2Cu3O7 on MgO substrates by off-axis magnetron sputtering

Abstract

Y1Ba2Cu3O7 thin films have been grown on MgO by off-axis magnetron sputtering using mixtures of argon, oxygen, and hydrogen. Reduction in film transition temperature resulting from cumulative target sputtering time (target degradation) is minimized by adding hydrogen to the sputtering gas. Without hydrogen, new targets which had produced films with 87.5 K transition temperatures degraded with deposition time and produced films with transition temperatures of only 82 K. After addition of hydrogen, these targets produced films with transition temperatures of nearly 89 K. Critical-current densities for the films made at optimum hydrogen flow were greater than 3×106 A/cm2 at 4 K. With the addition of hydrogen, we observed a significant increase in the sputtergun cathode voltage and a dramatic increase in the deposition rate. The films were predominantly c-axis oriented, and we observed a minimum c-axis lattice parameter for optimum hydrogen flow. We attribute these improvements in material properties to the catalytic effect of hydrogen in maintaining atomic oxygen in the plasma, allowing more oxygen to be incorporated into the target and the film during growth.