On The Mgo Substrate Ybco Hts Thin Film Growth Studies

Large-area double-sided YBCO high temperature superconductor (HTS) thin films with excellent electrical and microwave properties, which can improve the performance of the microwave passive devices, have been paid intensive attention. MgO substrate with isotropic dielectric constant and very low dielectric loss is very suitable for the application of the microwave devices. It is difficult to prepare YBCO film on MgO substrate because of the large lattice mismatch between MgO and YBCO, and the deliquescency of MgO in the air. The growth of YBCO thin film on MgO substrate aiming at these difficult issues was studied in this thesis. The content in detail is as follows:1. The influence of the substrate temperature, and sputtering pressure, etc. on the film structure, surface state and performance has been studied. By analyzing the microstructure, orientation and surface state, optimum process parameters were obtained: substrate temperature being 650℃, sputtering power being 0.5(×2)A, sputtering pressure being 30Pa, and PO2:PAr being 1:2.2. YBCO self-epitaxy method and MgO homogenous epitaxy method were adopted to improve its properties. The critical current density (Jc) of YBCO film was relatively higher than that of YBCO thin film prepared by common sputtering method.3. The improvement of Jc and in-plain and out-of-plain grain orientation of YBCO film had been realised by pre-annealing of MgO substrates. The properties of YBCO films deposited on the annealed substrates were greatly improved, with Jc=2.3MA/cm2, and Rs(microwave resistance)≈0.16m?, which met the requirement of high performance microwave device.4. The stability of YBCO film in different environments was discussed and further suggestion has been given for preserving the films.