HIGH-QUALITY YBA2CU3O7 FILMS ON 4-IN WAFERS OF SAPPHIRE, GALLIUM-ARSENIDE, AND SILICON

Our technique of reactive thermal co-evaporation has been extended to fabricate large films (up to 4 in.) of YBa2Cu3O7 with high quality. A rotating substrate holder is used to separate the deposition and oxida tion processes. This allows free access of the metal vapors. As large substrate wafers we use Al2O3, Si, and GaAs with buffer layers of CeO2 , YSZ, and MgO, respectively. On all substrates, the uniformity of thi ckness and composition was better than 2%. Inductively measured T(c) a nd j(c)(77 K) were 87.5 +/- 0.2 K and >1 x 10(6) A/cm2, respectively, across the full wafer area. This holds also for GaAs substrates due to a new procedure of capping by Si3N4.