The current status of epitaxial technology towards high Tc electronics is summarized. Properties and processing maturity were compared for various oxide single crystals to give hints for the choice of substrate. Such problems in YBa2Cu3O7 (YBCO) film growth as precipitate formation and cracking were quantitatively investigated and shown to be solved by carefully preparing the substrate surface and by optimizing buffer layers and growth conditions. It is now possible to perform ideal layer-by-layer growth of various oxide films on atomically flat substrates by laser MBE to explore not only high Tc electronics but also a possible new field of oxide electronics.
An overview of present Josephson junctions based on high-temperature superconductors (HTSs) is described. I indicate the importance of the critical current-normal resistance (IcRn) product, and show the experimentally-obtained values of the IcRn products for the HTS Josephson junctions reported so far. The junctions include grain boundary junctions, edge junctions, and sandwich junctions. Considering the charge transport mechanism across the junctions, effective ways to increase the IcRn product are proposed.
The cellular communication market is expanding dramatically, with bands near 1-2GHz being auctioned for use. The frequency spectral regions allocated for cellular communication are rather narrow, so they are certain to have a high density of communication channels. Thus, proper filtering of transmitting and receiving signals into the allocated bands, and precise channelization of the multiple simultaneous signals within each band, are essential for providing a high standard of customer service. HTS filters are expected to be used on circuit systems of the base station as the means to maximize frequency use. Bandpass filters are typically realized by appropriately coupling a set of resonant elements which may be in the form of three-dimensional cavities, bulk rods, or resonant structures. Though planar circuits like microstrip are especially attractive because of their compactness and low cost, even cooled copper metals are unable to achieve a Q value of even 1000. This low Q value is insufficient to support the low insertion loss and sharp filter skirts needed for selecting communication frequency bands. To receive circuit systems of the base station, a nine-pole, 3.7% bandwidth HTS filter designed by microstrip resonator configuration would have a dissipation-induced insertion loss of only 0.4dB including connectors at 898MHz and would have much better out-of-band rejection. However this HTS microstrip-type filter typically needs a single 2-inch wafer. The cooling system requires small-sized cooled components for long-life reliability. There have been some ideas devised for small-sized HTS filters. Filter circuits, one-third the previous size, have been successfully designed by using hair-pin circuits. In addition, a two-pole, 0.5% b