Ag-doped double-sided PLD-YBCO thin films for passive microwave devices in future communication systems

Abstract

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.

Microstructure and microwave surface resistance of typical YBaCuO thin films on sapphire and LaAlO3

“…Large-area pulsed laser deposition (PLD) was used to cover as-received 3 in r-cut sapphire substrates with 40 nm thick CeO 2 buffer layers and (250-350) nm thick YBCO films subsequently on both sides [18]. Also, YBCO targets doped with 4 to 7% Ag were used to improve the crystalline perfection and the smoothness of the films [19]. In addition, LaAlO 3 single-crystal cylinders for dielectric resonator applications were covered by PLD with epitaxial YBCO films on both opposite cube-indexed (100) faces.…”

Epitaxial CeO2 buffer layer on deliberately miscut sapphire for microcrack-free thick YBa2Cu3O7−δ films

“…For the fabrication of high quality YBa 2 Cu 3 O 7Àd (YBCO) films for large-area and highpower applications such as microwave devices [1,2] or fault current limiters [3], sapphire substrate buffered with CeO 2 is highly preferred. Especially, as switching elements for resistive fault current limiters, thick YBCO films are necessary to increase the critical current per unit width (i.e., J c t product, here J c is the critical current density and t is the film thickness) and thereby enhance the nominal power [4].…”

Oxide Thin Film Heterostructures on Large Area, with Flexible Doping, Low Dislocation Density, and Abrupt Interfaces: Grown by Pulsed Laser Deposition

“…In particular, the large-area substrate heater as shown in Figure 2 is the result of a series of prototype heaters with different designs of the heater element and the substrate Laser Chemistry YBCO wafer with two YBCO films at both wafer sides, demonstrating the very good homogeneity of j c using the " j c -scan Leipzig." As much as 15 consecutively deposited 71 × 75 mm 2 YBCO wafers showed such excellent j c -homogeneity, indicating a high reproducibility of the "space qualified" large-area PLD process [9][10][11]. rotation.…”