HIGH T_C SUPERCONDUCTING ELECTROMAGNETIC WAVE DETECTORS FOR MILLIMETER AND SUBMILLIMETER BANDS USING SILICON SUBSTRATES

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It is expected that high Tc superconducting millimeter and submillimeter wave devices such as a low loss transmission line and a high sensitivity detector, which can be operated with a simple cryogenic system, are applicable for a ultra high speed communication system in order to supply a communication demand. Specific high frequency properties of high T_C superconductors caused by the characteristic layred structure is also attractive from the application point of view. In this research project we aimed to develop fundamental technologies of electromagnetic wave detectors for millimeter and submillimeter bands using high T_C superconducting YBCO grain boundary Josephson junctions (GBJJ) on silicon bicrystal substrates. We have first succeeded a video detection of 2.525THz signal using YBCO GBJJs operated at 70K as a result of improvements of junction parameters such as the supercondcuting transition temperature, Tc and the I_CR_N product. Furthermore, we found that high frequency response (Shapiro step) was enhanced by a weak magnetic field application for wide frequency range up to submillimeter wave through microwave. This is a quite useful knowledge to develop a practical submillimater wave spectrometer using the GBJJ.Harmonic heterodyne mixing experiments were also performed using GBJJ for a submillimeter signal of f_S=2.525THz and a microwave signal of f_<LO>=19.4176268GHz then we had 130th harmonic mixing output {IF (Intermediate Frequency) output}. For the harmonic mixing we had the signal and noise ratio (S/N) of about 20dB and the spectrum resolution of 100KHz. The S/N would be improved to some extent by optimizing high frequency circuit design. In conclusion we have substantiated that the harmonic heterodyne mixing using GBJJs performs the high spectrum resolution for millimater and submillimeter waves and a precise spectrometer for the entire frequency range will be practical together with the video detection.