Double Layer Processes of LBMO/YBCO and Crystalline Degradations Oxide microwave devices will be widely expected in mobile communication system in the near future in the world. Superconducting YBa2Cu3Ox (YBCO) thin films are most advisable for microwave filter devices due to their very low surface resistance. Next generation devices are tunable microwave filters formed by double layers consisting of YBCO and ferromagnetic manganites such as La(Ba)MnO3 (LBMO).
In order to complete excellent double layers, we must first obtain proper techniques to fabricate perfect a/c-phases of YBCO and excellent crystalline LBMO single layers on substrate at low substrate temperatures (Ts), and then fabricate their double layers. We have tried an ion beam sputtering (IBS), then now we can control the perfect a-c orientation growths of YBCO. The minimum surface roughness is 1 nm for the c-phase and 0.3 nm for the a-phase.
Excellent crystalline thin films of LBMO can be grown by IBS with controlling Ts, oxygen pressure (Po) and oxygen molecular or plasma supply on MgO and LAO substrates. It can be grown down to 480 deg C. The minimum rocking half-width is 0.01 deg, and the minimum surface roughness is 0.8 nm. As-grown LBMO film shows different metal-insulator transition and Curier temperatures. The results are interpreted by a phase separation and magnetostriction.
The double layers of YBCO on LBMO and LBMO on YBCO were fabricated by IBS. In YBCO/LBMO, the excellent a/c-YBCO can be grown on the underlying LBMO at 600-650 °C. The crystallinity of overlying YBCO is nearly the same with that of the single layers on MgO and LAO. The mosaicity of YBCO is much better than that of the single layers on MgO and LAO. It is noticed that the underlying LBMO crystallinity can be improved, and the mosaicity is not degraded after the double layer deposition. A n inferiority is that the double layer surface is much degraded. Then we should fabricate the smooth underlying LBMO. In LBMO/YBCO, the excellent crystalline LBMO can be grown on the underlying a/c-YBCO at 650-700 deg C. The better crystalline LBMO grows on the better crystalline YBCO. The LBMO/a-YBCO clearly shows XRD peak separations while the LBMO/c-YBCO shows peak overlappings. The crystallinity of overlying LBMO is slightly poorer that that of the single layers on LAO. The mosaicity of LBMO is much poorer than that of the single layers of LBMO on LAO, but is almost the same with that of the underlying YBCO. It should be noticed that the crystallinity of underlying YBCO is degraded considerably after the double layer deposition. Then we should deposite the overlying LBMO at low temperatures. However a superiority is that the double layer surface is not degraded or rather improved. Now we are estimating time-dependence of the crystalline degradations on the single and double layers. YBCO crystallinity is easily degraded with time but LBMO is very stable. Then LBMO/YBCO is advisable in terms of a long term degradation.