Tham khảo tài liệu 'handbook of high temperature superconductor electronics part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 4 Step-Edge Josephson Junctions F. Lombardi Chalmers Institute of Technology and Goteborg University Goteborg Sweden A. Ya. Tzalenchuk National Physical Laboratory Middlesex England INTRODUCTION In the framework of high-critical-temperature Josephson Junctions HTS-JJs the development of grain-boundary GB junctions has represented an important innovation. The structures involving extrinsic interfaces are well established for metallic low-temperature superconductors. A similar approach in HTS multilayer technology remains very difficult for both physical the short coherence length as well as chemical surface instability reasons although significant progress has recently been achieved in the fabrication of the ramp-type multilayer JJs. These difficulties have motivated the fabrication methods of HTS-JJs to deeper exploit the unique combination of structure and properties of the high-critical-temperature superconductors. Soon after the discovery of the HTS superconductors it was realized that at least some of the grain boundaries in a polycrystalline material behave as weak links for the superconducting current. The IBM group 1 first managed to separate a single grain boundary and proved that it worked as a Josephson junction. Later the same group found a method to artificially create individual grain boundaries in otherwise single-crystalline thin films the bicrystal technol Copyright 2003 by Marcel Dekker Inc. All Rights Reserved. ogy 2 . The intrinsic Josephson effect in the c-axis direction 3 or the use of a controlled nucleation of grains with different crystallographic orientation the biepitaxial technique 4 are other examples of valid alternative methods to realize Josephson structures. In these methods intrinsic interfaces and or barrier layers determine the Josephson junction properties. The fabrication of devices which are useful in complex circuits requires however the optimization and a precise control of these intrinsic interfaces barriers. Among the .
