CVD of Bi-Sr-Ca-Cu-O Thin Films

Abstract

We developed a chemical vapor deposition (CVD) method for high-Tc superconducting Bi-Sr-Ca-Cu-O thin films, and obtained a high-Tc phase (about 110 K) without postannealing in an atmosphere containing oxygen. Films were deposited on (001) MgO substrates in He in an open-tube reactor with O₂ and/or H₂O oxidizing agents. The source materials --anhydrous metal halides such as BiCl₃, SrI₂, CaI₂, and CuI -– were evaporated in the CVD system to be used as source gases. The deposition temperature was between 700°C and 850°C. The average deposition rate was about 1.5 nm/min and the average film thickness was about 0.1 μm. Films were a mixture of low-Tc (about 80 K) and high-Tc (about 110 K) phases. Their C-axis orientation was perpendicular to the substrate. Their electrical resistance decreased abruptly below 115 K and the zero-resistance temperature was around 98 K. A critical current density of about 1.7 x 10⁴ A/cm² was obtained at 4.2 K. The O₂ in the CVD atmosphere played an important role in determining the phase of films at higher temperature depositions.