Fabrication Of Bismuth-based High-temperature Superconducting Films And Their Josephson Effect

Bismuth-based high-temperature superconducting materials exhibit the intrinsic Josephson effect(intrinsic superconducting tunneling effect)due to their layered crystal structure,and have important applications in the field of quantum devices such as superconducting quantum interferometers,superconducting computers and terahertz sources.However,because of the complexity of the crystal structure of bismuth-based superconducting materials,the preparation and microfabrication of single crystals,especially large-sized single crystals,are highly difficult.Therefore,it is of great importance to explore the preparation and new methods of microfabrication of these thin-film materials and the possibility of the intrinsic Josephson effect for the development of superconducting quantum devices.In this paper,we propose to study Bi2Sr2CaCu2O8+δ(Bi-2212)and Bi2Sr2Ca2Cu3O10+δ(Bi-2223)in bismuth-based superconductors,and explore the feasibility and controllability of the intrinsic Josephson effect in these materials on the basis of new methods for the preparation and microfabrication of these high-quality thin films,and furthermore,we also explore the possibility of the intrinsic Josephson effect in The feasibility of epitaxial growth of Bi-2212 on YBa2Cu3O7-δ(YBCO)to form Bi-2212/YBCO heterojunctions to produce the conventional Josephson effect was further explored.The main studies are as follows:(1)Bi-2212 superconducting thin films were prepared on LaAlO3(LAO)single crystal substrates by the sol-gel method.The effect of oxygen content on the orientation of Bi-2212 films during heat treatment was investigated,and the influence of film orientation on the critical transition temperature and critical current density was analyzed to explore the optimal conditions for the preparation of high-quality Bi-2212 films.The microstructure and epitaxial growth of Bi-2212 films on LAO substrates were observed by atomic resolution spherical aberration corrected transmission electron microscopy to analyze the atomic arrangement pattern and the feasibility of preparing intrinsic Josephson junctions.On this basis,the step-like three-dimensional microscopic patterns of Bi-2212 were prepared using the photoreceptive properties of sol-gel,and their I-V curves showed multiple voltage jumps,indicating that the biaxially woven Bi-2212 films would produce an intrinsic Josephson effect similar to that of single crystals.(2)In order to increase the number of tandem intrinsic Josephson junctions in the c-axis direction and to explore the feasibility of Bi-2212 thin film materials prepared by the sol-gel method for terahertz device applications,a process method for micron-scale thickness Bi-2212 thin films has been developed.This micron-thick Bi-2212 film with a biaxial weave leads to a significant increase in the number of intrinsic junctions in series along the c-axis,resulting in a significantly larger zero-voltage current and voltage range.Further analysis reveals that the I-V characteristics are similar to those of terahertz source devices prepared from Bi-2212 single crystals,promising their application in terahertz devices.(3)In order to obtain the intrinsic Josephson effect at higher temperatures,a new method for the preparation of(Bi,Pb)-2223 films with higher critical transition temperatures and their microfabrication was investigated.The effect of heat treatment process parameters on the preparation of(Bi,Pb)-2223 thin films is discussed and the phase formation mechanism is analyzed.The possibility of chelate formation between the chemical modifier and metal ions was investigated.The graphical(Bi,Pb)-2223 step-like 3D microfabrication I-V curves prepared by using its photographic properties showed multiple voltage jumps and biaxial weaving of(Bi,Pb)-2223.(Bi,Pb)-2223 films also exhibit the intrinsic Josephson effect.(4)The Bi-2212/YBCO heterostructure was formed by epitaxially growing Bi-2212 on YBCO,and a seven-layer atomic misalignment layer with a thickness of about 1.32 nm at the interface was found to act as a potential barrier layer,causing the heterostructure to exhibit an I-V curve with Josephson characteristics.The Bi-2212 and(Bi,Pb)-2223 high-temperature superconducting films prepared by the sol-gel method have perfect crystal structures and excellent electrical properties,and show intrinsic Josephson effects similar to those of single crystals after micropatterning them.Further prepared Bi-2212/YBCO superconducting heterojunctions show conventional Josephson junction effects and provide a basis for the development of bismuth-based high-temperature superconducting devices.