Development of Superhigh-Frequency Electromagnetic-Wave Detectors Using Grain-Boundary Junctions of BKBO

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Ba_<1-x>K_xBiO_3(BKBO)grain-boundary junctions fabricated on bicrystal substrates are Josephson tunnel junctions which show the SIS (superconductor-insulator-superconductor) feature. A highly-sensitive sensor for superhigh-frequency electromagnetic-waves is a candidate for the application of these junctions, utilizing the gap energy of BKBO wider than those of metal superconductors. In this research, we intended to develop the SIS mixers for the detection of super high-frequency electromagnetic waves using BKBO grain-boundary junctions, and studies on the use of low-permitivity substrates, the improvement of junction properties and the development of junction integration technology (high-frequency circuits) were carried out.1. Establishment of the technology for the deposition of BKBO thin films on low-permittivity substrates :In order to establish the technology for the deposition of thin films on low-permittivity substrates necessary for high-frequency application, we tried to prepar … More e BKBO thin films on Mg (permittivity : 10). Since the deposition of BKBO thin films of high quality on MgO is more difficult than on SrTiO_3 (STO), we investigated the effect of the substrate treatment, buffer layrs, etc. It was found that the in-situ annealing of the substrate before the deposition in the sputter chamber is effective, and BKBO films which shows properties similar to those on STO were obtained. A buffer BKBO layr deposited at a high substrate temperature for a short time prior to the deposition at the normal temperature for superconducting films gives a (100) BKBO film of high quality on (100) MgO substrate.2. Investigation of junction properties :We investigated the properties of the junctions on STO.The velocity of the electromagnetic wave in the barrier of the junction is an order smaller than that reported for junctions of other materials, which suggests the effect of the high permittivity of the substrate and the necessity of low-permittivity substrates.3. Study of high-frequency circuits :We studied the circuits for the basic experiments of the superhigh-frequency detector including junctions and other components such as antennas, etc. Less