PROCESSING DEPENDENCE OF THE INTERFACIAL MICROSTRUCTURE OF AG CONTACTS TO YBA2CU3O7-DELTA THIN-FILMS

The interfacial microstructure of three differently prepared silver co ntacts on c-axis oriented YBa2Cu3O7-delta (YBCO) thin films was examin ed using high-resolution transmission electron microscopy (HRTEM). For contacts prepared in situ by Ag sputter deposition on films maintaine d at elevated temperature and ex situ by Ag vapor deposition on films annealed in ultrahigh vacuum prior to metallization, regions of atomic ally sharp YBCO(001)/Ag interfaces were observed. In contrast, the cro ss-section HRTEM images of contacts prepared by in situ Ag deposition at room temperature reveal an amorphous interfacial zone, typically 20 angstrom thick. Scattered Y2O3 precipitates are found at the YBCO sur face of all three contacts. The data suggest that intrinsic reactions between Ag and YBCO(001) are negligible, and that the amorphous interf ace layer for in situ contacts to cold films must be ascribed to react ions with gaseous impurities in the sputter chamber ambient. In conclu sion, we strongly emphasize the importance of using ultrahigh purity p rocess gases in order to avoid formation of a resistive interfacial ba rrier.