LARGE-AREA DEPOSITION OF YBA2CU3O7 FILMS BY THERMAL COEVAPORATION

Reactive evaporation techniques cannot be simply scaled up for larger YBCO films because the zone of enhanced O2 pressure in front of the substrate will also increase in height and is impenetrable for the metal vapours. We have circumvented this problem by separating the evaporation and oxidation zones. Smooth films without any precipitates on a 10x10 mum2 scale could be fabricated on 30x30 mm2 MgO substrates. The homogeneity of the stoichiometry and of the thickness was 2%. Good normal state electrical properties have been achieved: rho(300 K)/rho(100 K) = 3.0 and rho(100 K) = 40 muOMEGAcm. The superconducting transition temperature was typically 87 K with a variation of DELTAT(c) less-than-or-equal-to 0.5 K over the sample area while J(c) at 77 K varied between 1 and 6.10(6) A/cm2. The microwave surface resistance at 77 K was found to be R(eff) = 60 mOMEGA at 87 GHz. In addition, we deposited YBCO films on 3 inch LaAlO3 wafers with T(c) = 86 K +/- 1 K and tested the feasibility of deposition of YBCO films on 4 inch silicon wafers with a YSZ buffer.