Progress in the growth of YBa2Cu3O7−x thin films by MOCVD and prospects for large area, low temperature deposition AIP Conf.

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An arrangement for large area PLD on 3-inch wafers is proposed. In order to get a homogeneous stoichiometry and thickness distribution and small variations of superconducting properties on the 3-inch diameter, the substrate is foreseen to be rotated and additionally laterally moved up to 45 mm during deposition whereas the laser plume remains fixed.YSZ buffer layers showed thickness homogeneity of 1% within 10 mm, of 4% within 2 inch and of 8% within 3 inch diameter, respectively. For in-situ deposited YBCO thin films on r-plane sapphire with YSZ buffer layer we inductively measured within 3 inch diameter values of the critical temperature Tc(90%) from 85.9 K to 86.7 K and values of the critical current density jc(77 K) from 1 × 106 to 2 × 106 A/cm2. However, up to now the degree of epitaxy of the YBCO thin films on r-plane sapphire with YSZ buffer layer is lower compared to YBCO on MgO(100) as determined by Raman spectroscopy. Nevertheless, large area PLD seems to be a very promising technique for homogeneous coating of 3-inch wafers by epitaxial oxide thin films.

Abstroci -Pulsed laser deposited (PLD) Agdoped Y B a~c u &~ (YBCO) thin films on both sides of 3-inch diameter sapphire wafers are used routinely for development of microwave filters for future communication systems. The reproducibly deposited YBCOAg films of about 250 om thickness show critical current densities of 4 W c m 2 at 77 K and laterally homogeneous maps of microwave surface resistance R off about 45 mQ at 145 GHz and 77 K measured by an open resonator technique. The R, at 8.4 GHz and 77 K determined in the center position of the YaBCO:Ag films with a sapphire resonator technique remains constant at about 380 pi2 up to a microwave surface magnetic field of 7-10 mT. Correlations of transport and microwave properties to the film microstructure are shown in terms of in-plane epitaxy, size of particulates on the films, and composition ratios C d O and Y/O, and growth defects like stacking faults as shown by Raman spectroscopy, SEM, and SNMS depth profiling, and TEM cross sections, respectively. The optimum Ag-content of the PLD-YBCO target was determined to be about 4 weight WO.The results demonstrate that Ag-doping supports the PLD process for YBCO in terms of reliability and cost effectiveness. R-mapping using an open resonator technique [51 providesinformation on lateral R, homogeneity over the 3 -inch diam~. film surface which is very important for control of lateral homogeneity of deposition process. The sapphire resonator measurements in dependence on microwave surface magnetic field at the center position of the wafers [6] give direct information on the power handling capability of the films, which is necessary for filter devices designed for higher transmitted power.Mapping of critical current density j, at 77 K is used as a simple and fast routine control of wafer quality employing im inductive and side-selective method [7]. Films with j, in the range 2 -4 W c m * are usually used for structuring of filters or R, measurements and we found lowest R values not imperatively correlated to highest critical current. Therefore, attempts are made to correlate the transport and microwave properties of the YBCO films to their microsmcture based on results of polarized Raman spectroscopy, cross sectional transmission electron microscopy (TEM), scanning electron microscopy (SEM). and depth profiling by secondary neutrads mass spectrometry (SNMS). In addition, the percentage of silver doping of the YBCO films was optimized concerning their microwave pedormance.

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