In the dissertation, the scientific problem of microwave electrodynamics of superconducting films Nb, MoRe, YBCO and their application in passive devices of superhigh - frequency (microwave) electronics has been solved. The use of superconductors in microwave electronics is very promising, as it allows to meet needs of more advanced devices compared to existing ones based on normal metals (copper, silver) and to create devices with much better parameters - high-quality resonators, filters and antennas with high signal sensitivity and selectivity, etc. However, there are problems specific to superconducting materials. In particular, it is necessary to reduce the residual surface resistance of the superconducting material in the microwave range, high-frequency energy losses associated with oscillations of magnetic flux trapped or induced by the microwave field associated with Abrikosov vortices, and the nonlinearity of the microwave response inherent in a superconducting material.
Superconducting YBCO films on sapphire and LaAlO3 substrates were obtained by pulsed laser deposition. Superconducting niobium films on sapphire substrates have been obtained by magnetron DC sputtering with the addition of a small component of a radio-frequency current. Superconducting films of the MoRe alloy on polycortical substrates were obtained by magnetron sputtering. The studied microstrip structures were fabricated using standard photolithography and subsequent etching, and then placed in a cryostat. The frequency response of the samples was measured using a vector circuit analyzer that operated in an automatic mode in the range from 300 kHz to 3.6 GHz and had a dynamic power change range of 40 dB. During the frequency response experiment, the values of the loaded Q factor and the resonant frequency have been calculated.
Numerical calculations (the method of moments) were used to obtain the frequency response of microstrip resonators with different topologies, and copper with a thickness of 10 μm greater than the thickness of the skin layer was chosen as the material. Using the resulting dependence of the quality factor on the frequency and calculating the value of the surface resistance of the copper microstrip, the frequency dependences of the frequency-normalized geometric factor were obtained. It has been shown that the geometric factor increases significantly with increasing frequency for all topologies in the form of a meander, and takes fixed values for topologies in the form of segments and fractals Using approximations of the surface resistance of YBCO film and the calculation of the copper film surface resistance, the frequency dependences of the surface resistance of YBCO and copper films in a wide frequency range were constructed and it was estimated that the studied HTSC films should be used as a replacement for traditional materials.
Experimental studies of magnetic-field and temperature dependences of electrodynamic parameters of thin YBCO films were performed at the minimum possible microwave signal power of -40 dBm. It was the way for achieving a linear mode of the microwave response of superconducting films. The measured dependences of the change in the real and imaginary parts of the complex resistance on the magnitude of the magnetic field induction B were linear, i.e., the change in the complex resistance was proportional to the magnetic field induction . This indicated that there were no weak links in the samples. It was shown that the dependence of the Labush parameter kp and the viscosity coefficient on the magnetic field to large values of the magnetic field (~ 1T) was not observed. This indicates that the individual pinning mode was implemented, even near the critical temperature, which may be due to the presence of a large number of long linear and planar defects formed in YBCO films during the deposition. The angular dependences viscosity and kp showed the presence of maxima for the parallel plane of the film of the magnetic field orientation 0o, which may show the presence of internal pinning due to the layered structure of YBCO films.
Practical implementations of broad-band and narrow-band microwave superconducting filters made of high-temperature superconducting YBCO films is considered. An experimental comparison of the characteristics of superconducting and copper filters showed significant advantage in the use of superconductors in realizing filters with unique characteristics. Dependence of the variations in the bandwidth loss of a narrow-band YBCO filter on the applied microwave signal power was measured while the presence of a nonlinear response in superconducting filters has been demonstrated. According to the results of the research, we conclude that it is possible to apply superconducting YBCO filters with only small values of the microwave input signal power.
