Joint study on application of oxide superconducting films.

利用氧化物超导体实现高频器件对制备小表面电阻薄膜具有重要意义。高质量的胶片具有较小的Rs值。山形大学与卡尔斯鲁厄核研究中心合作研究的目的是：(1)建立高质量薄膜的制备技术。高质量薄膜是由山形大学的MOCVD方法和卡尔斯鲁厄核研究中心的圆柱靶磁控溅射制备的。用MOCVD法制备了略大面积的YBCO薄膜(50×50 mm~2)，用溅射法制备了外延薄膜。(2)表面阻抗测量系统的建立。BSCCO和YBCO薄膜的Rs值均在超导转变温度以下降低，超导状态下的Rs值约为5mOmega。(3)缓冲层高频器件需要较小的介电常数衬底。硅和蓝宝石的介电常数很小，但这些衬底很容易与YBCO发生反应。研究了保护衬底与YBCO反应的缓冲层NdGaO_3。采用溅射法在硅衬底上制备了c轴取向的NdGaO_3薄膜。

The realization of high frequency devices using oxide superconductors is very important to prepare small surface resistance films. High quality films have small Rs values. The purpose of joint study between Yamagata University and nuclear research center of Karlsruhe is as follows.(1) Establishment of the preparation technique for high quality films.The high quality films are prepared by MOCVD method in Yamagata University, and by magnetron sputtering with a cylindrical target in nuclear research center of Karlsruhe. We get slightly large-area YBCO thin films (50X50mm^2) by MOCVD and epitaxial films by sputtering.(2) Establishment of the measuring system of surface impedance.The surface impedance of superconducting films is measured by a strip-line resonating method. The Rsvalues of BSCCO and YBCO films decrease below superconducting transition temperature and the value of BSCCO at superconducting state was about 5mOMEGA. .(3) Buffer layerSmall dielectric-constant substrates are needed for high frequency devices. The dielectric constant of Si and sapphire is small, however these substrates easily react on YBCO. We study the buffer layer, NdGaO_3, which protect the reaction between substrate and YBCO. We prepared c-axis oriented NdGaO_3 films on Si substrate by sputtering.