The Preparation And Superconductivity Research Of MgB₂ Films

The superconductivity in magnesium diboride(MgB₂) was discovered in 2001, after that, the remarkable high transition temperature attracted a lot of interest from allover the world, and this has renewed the research of basic properties of those simple binary compound materials. Now we know that MgB₂ is a phonon-mediated BCS superconductor, which has two energy gaps and a long coherence length and so on. Great progress has been made in the fabrication of MgB₂ thin films. In this paper, we use two different way to prepare the MgB₂ films: the first is two-step ex-situ chemistry vapor deposition method (CVD), including two process: the precursor boron films deposition and post-annealing. The other one is one-step in-situ hybrid physics-chemistry vapour deposition (HPCVD) method. The main points were summarized as below:1. In the experiments of ex-situ two-step large—area films growth, we used high purity B₂H₆ as B source, in high-vacuum films—plating machine and grew excellent precursor boron films on the underlay of Al₂O₃ polycrystalline, 65mm×50mm in size. After annealed with pure magnesium (Mg) in the sealed Ta crucible, the superconducting MgB₂ films were formed at last. We used kinds of experiments to measure the superconducting character, including XRD,SEM,XPS and SQUID and so on, found that the film has a transition temperature around 39K , the currents density was about 3×10⁷A/cm² for this films. The film has a stable superconducting even under a large magnetic fields around 30K. and this results indicated this method was matured now and suitable for the industrial manufacture of MgB₂ superconducting films.2. on the basis of CVD superconductor films preparation method, we developed a new method to deposit MgB₂ films, called in-situ hybrid physics—chemistry vapor deposition with two heater. We prepared MgB₂ superconducting films on underlay of Al₂O₃ polycrystalline successfully by the method, the experiments showed the films had a superconducting transition temperature of 38.5K,ΔT_c was about0.5K.3. Discussed the application prospects of the MgB₂ superconducting films in the micro-electronics area, combined the ex-situ two-step method and in-situ one-step method, we could get two-layer or multilayer structures of MgB₂ superconducting films. This layer structure is the base of Josephson junction and RSFQ devices. The combination of those two methods has special meanings for the superconducting connections of the integrated circuit.