| Microwave passive devices made by high temperature superconductor thin films (HTSTF) are more and more widely used in civilian communication equipment and front ends of radar detection equipment. As the industrialization of high temperature superconductor moves on, the requirement of high quality HTSTF is increasing rapidly. During the fabrication process of thin films, the quality of thin film can be detected by measuring the surface resistance(Rs) of HTSTF and this is helpful to the adjustment of fabrication process. In the aspect of device design, the design efficiency of high performance superconductor microwave device can be guaranteed by measuring the Rs of HTSTF accurately. Therefore Rs measurement of HTSTF is significant in the industrialization of HTS. In the research of mechanism of superconductor, the relationships between Rs and other physical quantity such as frequency and temperature are always the concern of the researchers. Since correct theory requires verification in experiment, the measurement of Rs of HTSTF is also indispensable in the research of superconductor. Image dielectric resonator method, which is one of the testing methods for microwave surface resistance of HTSTF, has the advantages of single piece measuring, nondestructive testing, short measuring time and high accuracy. Therefore, image dielectric resonator method is adopted as the supplement of Chinese national standard for the measurement of Rs of HTSTF. In this dissertation, the researches on image dielectric resonator method for microwave surface resistance measurement of HTSTF are as following.Calibration in image dielectric resonator method was examined in depth and two selecting methods which were called "filtering" and "eliminating" using resonator cavity and testing probe respectively for choosing match sapphire rods were proposed. By using these methods, perfect conductor plane has been achieved at the interface of testing probe and calibration probe, so that the accuracy of the value of A was improved. Gold coated copper plate was used as the sample and its microwave surface resistance was known for the calibration in the image method. Since gold is very stable, the variation of the value of Rs caused by oxidation is neglectable and the accuracy of the value of B is improved. A cylindrical hollow resonant cavity using TE013 mode was fabricated for measuring the Rs value of the gold coated copper plate. The measured Rs value is 66.74mΩat 12GHz and 77K. Two methods using 50Ωload and lossy dielectric material respectively for the improvement of calibration probe was proposed. By these two methods the symmetry of testing probe and calibration probe was achieved. Contrasting measurement between improved device using image method and device using two-dielectric-resonator method has been done. The standard deviation and relative standard deviation of the results in the contrasting measurement are 0.038 mΩand 5.2%. The relative standard deviation is much less than 20% which is the maxium uncertainty proposed in the international standard of the microwave surface resistance measurement of HTSTF. Multimode image dielectric resonant method for Rs measurement was proposed in this dissertation. A measuring device using TE011, TE012, TE021 and TE013 modes was fabricated. By using the four modes of the device the surface resistances of superconductor thin film at four different frequencies(11.03 GHz, 17.38GHz,19.15GHz and 25.33GHz) were measured. After the calibration process of this multimode measuring method, the frequency characteristic of surface resistance for testing sample can be described within one temperature cycle.
|
PDF Full Text Request