Tl系薄膜合成の現状

抄録

This review contains recent information on the properties of Tl-Ca-Ba-Cu-O thin films. The conditions for the Tl-Ca-Ba-Cu-O film growth by sputtering and by molecular beam deposition are described. The highest zero resistance temperature is 116K. The as-deposited films are insulators, but they become superconductive after being annealed in oxygen at 880930°C for 10min. After post-annealing, the films on MgO and SrTiO₃ substrates exhibit zero resistivity at 116K and 80K, respectively. The crystal structures of the films are tetragonal, so that the surface morphologies are essentially twin free.
Using a SQUID magnetization measuring technique in a parallel field, it was found the randomly oriented polycrystalline Tl-Ca-Ba-Cu-O thin film shows a critical current density (J_c) in excess of 1.5×10⁶A/cm² at 50K. This large J_c value indicates the presence of surface pinning, which is much stronger than any bulk pinning observed by a measurement in a perpendicular field.
It was also found that the microbridge DC-SQUID's fabricated from the Tl-Ca-Ba-Cu-O films patterned by maskless etching using focused ion beam (FIB) processes, operates up to 95K.