The Preparation Of MgB₂Superconducting Thin Films And MgB₂Josephson Junction By Electron Beam Annealing

As the highest metal compounds superconductor, MgB2has a lot of advantages, such as higher superconducting transition temperature TC(39K), simple structure, higher critical current density and no weak links between its grain boundaries that exsits in high-temperature superconductors. As a result of the significant application in the high magnetic field, MgB2has aroused widespread concern in the scientific community. Since modern electronic components are based on membrane, scientists from various countries have a great interest in the preparation of MgB2superconducting thin films along with the discovery of MgB2superconductivity. MgB2critical temperature is much higher than that of the Nb alloy superconductors and it can work at more than4.2K, which makes it optimistic about the prospects. Josephson junction and superconducting quantum interference device (SQUIDs) made of MgB2can also work at more than20K.In this paper, MgB2superconducting thin films were prepared by PVD method and electron beam annealing method. After getting the best annealing parameters, we tried to synthesize the MgB2-B-MgB2Josephson junction.First, the feasibility of fabricating MgB2superconducting thin films by electron beam annealing is investigated. The key factor to fabricate MgB2superconducting thin films with electron beam annealing is that the temperature in the MgB2precursor films could rise to a right value which is suitable for the combination of Mg with B while exposed by electron beam. By studied the mechanism of electron beam surface modification and temperature distribution of electron beam annealing, it is concluded that the electron beam annealing could meet the demand on temperature which is suitable for the combination of Mg with B to compose MgB2. The valid penetrating depths of high energy electrons in precursors are simulated by Monte Carlo method, a reference to select a suitable accelerating voltage is provided. Finally, the MgB2superconducting thin film with a superconducting transition temperature of33.2K is fabricated by the electron beam annealing.Second, we studied the effects of different ratio of Mg and B to MgB2superconducting thin films. A series of different Mg/B proportion of MgB2thin films have been measured. We can get the highest superconducting transition temperature while Mg was more than20%to30%. In order to get a better MgB2thin film, the beam current on superconductivity of MgB2thin film is investigated. Beam current is one of the key factors which affect the electron beam annealing. In this report the experiments are conducted in EBW-6electron beam welder at accelerating voltage32kV, beam diameter1.41cm and annealing duration0.2592s. The results show the superconducting transition temperature increased gradually when the beam current increased from9.9mA to12.8mA and decreased gradually when the beam current increased continually. Under above conditions, the best current should be between10.7mA and12.8mA. While the annealing current is12.8mA, the current density is4.9X106A/cm2under15K..Lastly, MgB2-B-MgB2multilayered films was fabricated on6H-SiC(001). We obtain the superconducting transition temperature of30K for MgB2Josephson junction which has a current density of2A/cm2by current-voltage measurement.