Study On Preparation And Properties Of YBCO Grain Boundary Junctions

Josephson junction is the core component of superconducting electronic devices,which directly determines the performance of superconcducting devices.Therefore,the preparation of Josephson junctions with good properties has become one of the research focuses of high lemperature superconducting electronic devices.Among them,grain boundary junctions have attracted much attention because of their control lable parameters,and they are easier to produce than other Josephson junctions.In this experiment,YBCO grain boundary junctions were prepared to test whether they have Josephson effect.The main contents and conclusions arc as follows:First the photosensitive sol gel method was used to prepare the BaxSr1-xTiO3(BST)film with ultraviolet photosensitivity on the substrate of LaAlO3.The step was fabricated by photolithography on BST thin film,the height of step was 146nm and the edge of step was flat,which laid a foundation for the formation of step junction by YBCO thin film growth on it.Secondly,a series of micron grade YBCO microbridges(minimum up to 5 microns)perpendicular to the edge of the step were prepared by photoreceptor sol-gel method,forming a YBCO/BST step-type microbridge grain boundary junction.The grain boundary junctions of YBCO/BST step-type micro-bridge with 5 microns were measured.R-T curve test shows that the resistance of step junction decreases with the decrease of temperature;V-I curve test shows that the voltage remains unchanged when the negative current decreases,and the voltage increes first and then decreases when the positive current increases.Subsequently,CeO2 thin films on SrTiO3 substrates were prepared by sol-gel method,and the effect of heat treatment process on the orientation of films was investigated.The results showed that a good(220)orien ted CeO2 gel film could be obtained after the pretreatment of 10min at 80℃ and the final treatment of 1h at 1000℃,which laid the experimental foundation for subsequent preparation of YBCO/CeO2 epitaxial junction.Finally,CeO2 gel film was prepared on SrTiO3 substrate by photosensitive sol-gel method,and then YBCO thin films were prepared on the substrate,forming YBCO/CeO2 epitaxial junction.R-T test shows that the resistance decreases sharply when the temperature drops below 88 K.V-I curve test shows that the voltage and current are linear when the temperature drops above 90 K,and the voltage from 50 K to 80 K is non-linear.