Characterization of the surface impedance of a superconducting thin film with application to propagation characteristics of surface acoustic waves

摘要

In this paper, an algorithm suitable for the computer aided design (CAD) has been developed to estimate and model the main characteristic parameters of superconducting thin films. The detailed parameters of the superconducting thin film such as the surface impedance are described with the aid of the two-fluid model. An impedance function that varies with the temperature and frequency has been obtained. The attenuation constant has been also computed and presented. The obtained results show that, within a certain range of temperature, the surface impedance exhibits a negative real part. This negative resistance phenomenon is indicative of amplification which may occur if the superconducting thin film is embedded in a proper microwave circuit. It can be seen that, the attenuation strongly depends on the frequency and the dispersion-less behavior of the superconducting thin film can be observed. As an application, the obtained surface impedance of a high Tc superconducting thin film can be used to study the propagation characteristics of a surface acoustic wave (SAW). As a result of low loss and hence negative part, the implementation of high gain surface acoustic wave amplifier becomes possible. The computer simulation results are verified by comparison with results using the surface impedance formula of Mattis-Bardeen theory and show a good agreement.