.sto / Integration Of Ybco Thin Film Pulsed Laser Deposition And Performance Research

The dielectric constant of SrTiO3(STO) thin films is voltage-dependent near the curie temperature Tc (about 40K) . And no dispersion in εis observed in STO at frequencies up to 10 GHz.YBa2Cu3O7-x(YBCO) high temperature superconducting thin film has very low microwave surface resistance. The typical value of Rs(10GHz,77K)is smaller than 1mΩ. In addition, Similarities in crystal structure and chemical compatibility between STO and YBCO open up the possibility that the unique properties of each of these films can be combined to develop an array of tunable microwave devices with novel applications such as filters, phase shifters and resonators. The major task of the dissertation is the growth of YBCO/STO for the fabrication of microwave devices.The STO, YBCO and STO/YBCO thin films were deposited on LaAlO3 (001)(LAO) substrate by pulsed laser deposition(PLD). The effects of deposition parameters, such as the substrate temperature, the of target-substrate distance, laser energy density, on the properties of the thin fillms were systematically studied. The surface morphology of the thin films was investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Under the optimized condition, the surfaces of the thin films were smooth. The root mean square roughness (rms) of STO thin film was 0.77nm in the range of 10μm. The step-flow growth mode of STO thin film was achieved. The X-ray diffraction (XRD) results showed that both STO and YBCO thin films were c-axis oriented. The superconducting transition properties of YBCO thin films were excellent, Tc0 >90K,ΔTc<1K. In order to demonstrate the dielectric properties of STO thin film, the sandwich-type capacitors and interdigitated capacitors were fabricated. The properties of capacitors were measured using an HP4284A LCR meter at 77K under 100kHz. The measurement results from sandwich-type capacitors showed that the dielectric constant decreased from 1437 to 902 when the electrical field increased from 0 to 56kV/cm.The tunability was 38% and the dielectric loss was 1.06%.The asymmetry on the C～V curve was observed. It was attributed to the formation of series capacitance by the STO thin films and the interface between STO and the bottom electrode. The measurement results from interdigitated capacitors demonstrated that the tunability is 21% when the bias is 40V and the loss is 0.25%.