Exploitable results
High temperature superconducting Josephson elements based on artificially generated, engineered grain boundaries are being fabricated and evaluated. Important issues are the controllability, reproducibility and feasibility of the fabrication process, as well as the reliability, application potential, performance limits and physics of the fabricated devices.
Engineered GBJs of the bicrystal and step edge type have been prepared using the lithographic, ion beam etching and film deposition facilities of the consortium. Furthermore, parallel and series arrays of bicrystal GBJs have been fabricated in a reproducible and controllable way. The GBJs were characterized with respect to their low frequency, high frequency, and noise properties. In addition, the spatial homogeneity of the electrical transport properties of GBJs has been analysed by low temperature scanning electron microscopy (LTSEM). Furthermore, a new method for the determination of the supercurrent correlation function has been developed.
In improving the fabrication process of bicrystal GBJs a spread of the junction parameter of less than 30% on the same substrate could be achieved. The noise temperature of bicrystal and step edge GBJs was found to be consistent with the sample temperature and junction resistance. Under certain conditions, large excess noise was found and was attributed to fluxon fluctuations. Using LTSEM flux states in bicrystal GBJs could be imaged. Based on parallel arrays of bicrystal GBJs magnetic field effect 3-terminal devices showing a current amplification of up to 5 have been fabricated.
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