Preparation And Preliminary Application Of Magnesium Diboride Superconducting Films

Though one had known the existence of magnesium diboride in1950, people had not paid much attention to it before. Things changed till the superconductivity of MgB2was discovered in2001. The transition temperature (Tc) of MgB2is about39K, and this attracted a lot of interests from scientists all over the world.Not only the Tc of MgB2is higher than that of the limit of BCS theory’s prediction for simple intermetallic compounds, but also it has many special superconducting characteristic compared with many other traditional superconductors. Therefore the superconductivity of MgB2is significant both in academic investigations and material applications.In this paper, the preparation processes of MgB2superconducting films were presented in detail. MgB2films were grown via two methods:one is called two-step ex-situ chemical vapor deposition (CVD) method, the other is the one-step in-situ hybrid physical-chemical vapour deposition (HPCVD) method. Main outcomes of this work are summarized as follows:1. In the experiments of ex-situ two-step large-area films growth, by using high purity B2H6as the B source, precursor boron films were deposited in a high-vacuum chamber on the substrate of Al2O3polycrystalline. Then the samples were annealed in magnesium (Mg) vapor in a sealed Ta crucible to form superconducting MgB2films. The samples were characterized by XRD, SEM, XPS and SQUID. The results indicated that the film has a transition temperature of39K. The current density was about1.8×106A/cm2. The preparation method was matured and suitable for the pratical application.2. An in-situ hybrid physical-chemical vapor deposition process with double heaters was developed. The prepared MgB2superconducting films on the subatrate of Al2O3polycrystalline and single crystal substrate showed a superconducting transition temperature of38.5K, about a transition width of0.5K, and a current density of1.0×105A/cm2.3. A method to fabricate sandwiched MgB2-B-MgB2multilayer structure was invented. The method may be a viable approach to the fabrication of Josephson junction.4. Two patterning techniques for MgB2superconductiing films were developed. Especially the technique by patterning the precursor boron film first and then annealed in magnesium vapor to form the patterned MgB2films, has the characteristics of easy to implement and high resolution. These techniques are important prerequisite to fabrication of Josephson junction and RSFQ devices, and the possible superconducting interconnection for the integrated circuits.