Preparation Study of Bi-Sr-Ca-Cu-Oxides Superconducting Thin Films by Resistive Evaporation

Abstract

A conventional vacuum system housing resistively heated sources only was used to study the evaporation conditions for Bi-Sr-Ca-Cu oxides thin film production. Thin film were prepared by sequential evaporation of CaF₂, SrF₂ and Bi pulverized mixture and Cu from the two separate sources. The starting materials were weighed to yield a stoichometric Bi₂ Sr₂ CaCu₂ film of about 1μm thickness upon evaporation to completion. Well polished MgO Substrates kept at room temperature were used in this experiment.

The films were annealed in a quartz-tube furnace at 350°C for one hour for oxidation of the copper layers thus precluding any Bismuth escape, followed by 10 minutes at 725°C in flowing O₂ bubbled through water for defluorination and then at Ca. 870°C for 14 hours.

Typical results, using four-point probe method reveal a T_c (R = 0) at 83K and critical current density of 10³ A/cm² at 66K.

This work presents one of the simplest vacuum deposition methods in which no thickness monitor or any other control system is required. The crucial point in the heating treatment was to overcome the problem of the Bismuth diffusing out of the film during the long annealing time at high temperature.