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

低损耗传输线、高灵敏度探测器等高Tc超导毫米波和亚毫米波器件可在简单的低温系统中运行，有望应用于超高速通信系统，以满足通信需求。从应用的角度来看，高T_C超导体的特殊高频特性也是有吸引力的。在本研究项目中，我们旨在利用高T_C超导YBCO晶界Josephson结（GBJJ）在硅双晶衬底上开发毫米波和亚毫米波探测器的基础技术。由于改进了超导转变温度、Tc和I_CR_N积等结参数，我们首次使用工作在70K下的YBCO GBJJs成功地检测了2.525THz信号。此外，我们发现弱磁场通过微波在宽频率范围内（高达亚毫米波）应用增强了高频响应（夏皮罗阶跃）。这对于利用GBJJ研制实用的亚毫米波光谱仪是非常有用的。在f_S=2.525THz的亚毫米信号和f_<LO>=19.4176268GHz的微波信号下，利用GBJJ进行了谐波外差混频实验，得到了第130次谐波混频输出{IF （Intermediate Frequency）输出}。对于谐波混合，我们的信噪比（S/N）约为20dB，频谱分辨率为100KHz。通过优化高频电路设计，可以在一定程度上提高信噪比。综上所述，我们已经证实了使用GBJJs的谐波外差混合对毫米波和亚毫米波具有高的频谱分辨率，并且在整个频率范围内使用精确的光谱仪以及视频检测是可行的。

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.