过耦合结构超导铝共面波导谐振器温度特性研究

Temperature characteristics of over coupling superconducting coplanar waveguide resonator based on aluminum film

制备了基于超导铝膜的四分之一波长反射型共面波导谐振器,并利用矢量网络分析仪测量了该谐振器在低温超导状态下的传输特性。实验结果表明:对于拥有较大耦合电容的超导共面波导谐振器,在超导状态下随着环境温度的升高,超导薄膜的表面阻抗会增大,进而谐振器的中心谐振频率降低,谐振峰变宽。温度越高,谐振频率随温度升高而向低频偏移的速率越快。另一方面,随着环境温度升高,谐振器的外部耦合品质因数和负载品质因数也都会降低。温度越高,谐振器品质因数随温度升高而降低的速率越快。用二能级理论解释了实验现象,品质因数理论计算值与实验测量结果相接近。

In this paper, the design and fabrication processes of a quarter-wavelength superconducting Al film coplanar waveguide resonator with a large coupling capacitance were presented. The transmission characteristics of the superconducting resonator were measured by a vector network analyzer. The experimental results show that the operating temperature has a great influence on the characteristics of the quarter-wavelength superconducting coplanar waveguide resonator with the over-coupling design. As the operating temperature increases, because of the influence of the surface conductivity and dynamic inductance of the Al film, both of the resonance frequency and the Q value of the resonator decrease monotonously. Furthermore, the two-level theory was used to explain themeasurement results. The theoretical calculating result of the Q value agrees well with the experiment.