Fabricationof Josephson junctions using AFM nanolithography

[摘要] ENGLISH ABSTRACT: Planar weak link structures, such as micro-bridges, variable thickness bridges and nanobridges,have always attracted a lot of attention. Their potential to behave as real Josephsonelements make them useful devices, with numerous applications.Powerful techniques, such as focused ion-beam and electron-beam lithography, were successfullyused and are well understood in planar weak link structure fabrication. In thisdissertation the results of an experimental study on planar weak link structures are presented.For the first time these structures have been successfully fabricated using AFMnanolithography on hard high-temperature superconducting YBCO tracks, where diamondcoated silicon tips were used as a ploughing tool.Superconducting YBCO thin films were deposited on different substrates, using invertedcylindrical magnetron sputtering. The films were used to fabricate micro-bridges, variablethickness bridges and nano-bridges, by using conventional photolithography, argon ion-beammilling and AFM nanolithography.The measured I-V characteristics of the fabricated micro-bridges (width down to 1.9 µm),variable thickness bridges (thickness down to 15 nm) and nano-bridge (width down to 490nm) showed well defined DC and AC Josephson effect characteristics.For better understanding of the behaviour of these types of weak links, critical current versustemperature measurements, and magnetic field modulation of the critical current measurements,were also performed, with the results and discussions given inside the chapters.The major challenges that were experienced in the laboratory during the fabrication processesand the operation of the fabricated devices are also discussed, with the solutions givenwhere appropriate.

[发布机构] Stellenbosch University