On the effect of processing parameters in the chemical-vapor deposition of YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]] thin films on polycrystalline silver

Results are reported from an investigation of the effects of selected processing parameters on the morphology and properties of YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]] (YBCO) superconducting thin films grown directly on polycrystalline silver substrates by chemical-vapor deposition (CVD). These results were achieved through a set of experimental studies which examined: (i) recrystallization mechanisms of polycrystalline silver and their effect on the deposition of YBCO thin films; and (ii) CVD processing conditions leading to the growth of high-quality YBCO films. The samples were analyzed using dynamic impedance, four-point resistivity probe, x-ray diffraction, Rutherford backscattering, and scanning electron microscopy. These studies showed that substrate temperature played a critical role not only in the formation of YBCO films, but also in the recrystallization of silver substrates, which in turn greatly influenced film growth. The studies also led to the identification of a two-stage processing scheme for the growth of YBCO films on silver. The first processing stage consisted of a substrate conditioning cycle which involved a 10 min ramping from room temperature to deposition temperature where the substrates were held for an additional 10 min in a flow of 70 sccm O[sub 2] at a reactor working pressure of 2 Torr. The second processing stage involved actual film deposition at 760--800 [degree]C for 3--10 min (depending on desired film thickness) in a mixed flow of 70 sccm O[sub 2] and 210 sccm N[sub 2]O at a reactor working pressure of 4 Torr. Samples thus produced were highly oriented along the [ital c] axis perpendicular to the substrate with a zero resistance transition temperature of 87 K and a critical current density of 2[times]10[sup 4] A/cm[sup 2] (77 K, [ital B]=0).