介质谐振器测量超导薄膜的微波表面阻抗

发布时间：2018-12-11 11:57

【摘要】：超导薄膜的微波表面阻抗Zs=Rs+iωμ0γ是它的一个重要性能指标,其中Rs是表面电阻,Xs是表面电抗。Rs表征超导薄膜的微波损耗,反映了准粒子的密度；x。正比于磁穿透深度,反映了电子对的密度,从它随温度的变化关系,还可以得到超导能隙的有关信息,因此精密测量这一参数对于了解材料的物理和电子学特性,发展新材料和设计超导电子学元件都有重要意义。本文中所采用的测试方法为蓝宝石介质谐振器法,它用超导薄膜单端短路在介质谐振器的一端,通过测量微波介质谐振器的品质因数Q和谐振频率f0随温度变化的关系来确定超导薄膜的微波表面阻抗。由于介质损耗在低温下非常小,谐振时绝大部分电磁能量集中在介质内部,辐射损耗低,因此谐振腔的品质因数高；另外蓝宝石介质的介电常数的温度稳定性很高,因此可以近似认为谐振器的频率随温度的变化主要来自于超导薄膜穿透深度随温度的变化。因此介质谐振器可以较精确地测量超导薄膜的表面阻抗。本文设计和制作了一个工作于TEo1s模式,谐振频率在18.3GHz左右的蓝宝石介质谐振器,其无载品质因数在3K时可达到130900。用此方法可以对薄膜进行无损伤测量,测量后的薄膜还可继续使用。通过测量和计算两片Nb超导薄膜和两片NbN超导薄膜样品的表面阻抗、穿透深度、电导率等,来验证整个测试系统的准确与否,同时也可以从数据中反应出我们的测试系统存在哪些问题存在,以及将来如何解决这些问题等。
[Abstract]:The microwave surface impedance (Zs=Rs I 蠅渭 0 纬) of the superconducting thin films is one of its important performance indexes, in which Rs is the surface resistance and Xs is the surface reactance. Rs characterizes the microwave loss of the superconducting films and reflects the density of quasiparticles. It is proportional to the depth of the magnetic penetration and reflects the density of the electron pair. From the relationship between the electron pair and the temperature, the information about the superconducting energy gap can also be obtained. Therefore, the precise measurement of this parameter is useful for understanding the physical and electronic properties of the material. The development of new materials and the design of superconducting electronic components are of great significance. The test method used in this paper is the sapphire dielectric resonator method, which shortens the dielectric resonator at one end of the dielectric resonator by using a single end of the superconducting thin film. The microwave surface impedance of the superconducting film is determined by measuring the relationship between the quality factor Q and the resonant frequency f _ 0 of the microwave dielectric resonator. Because the dielectric loss is very small at low temperature, most of the electromagnetic energy is concentrated in the medium and the radiation loss is low, so the quality factor of the resonator is high. In addition, the temperature stability of dielectric constant of sapphire medium is very high, so it can be approximated that the frequency of the resonator varies with temperature mainly because the penetration depth of superconducting film varies with temperature. Therefore, the dielectric resonator can accurately measure the surface impedance of the superconducting film. In this paper, a sapphire dielectric resonator working in TEo1s mode with resonance frequency of about 18.3GHz is designed and fabricated. Its no-load quality factor can reach 130900 at 3K. The method can be used to measure the film without damage, and the measured film can be used. The surface impedance, penetration depth and conductivity of two Nb superconducting films and two NbN superconducting films were measured and calculated to verify the accuracy of the whole testing system. At the same time, it can also reflect from the data what problems exist in our test system and how to solve these problems in the future.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.2

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