Deposition of thallium-based superconducting thin films by a simple thermal evaporation method

Superconducting Tl-Ca-Ba-Cu-O thin films less than 1 mu m thick have been prepared on Y-stabilized ZrO₂ (100), MgO (100), and SrTiO₃ (100) substrates using thermal evaporation and a two-step annealing process involving the growth of BaCuO₂ films followed by ex situ crystallization and thalliation under thallium oxide vapours. The authors have been able to fabricate reasonably uniform films of the Tl₂Ca₁Ba₂Cu₂O_x (2122) and Tl₂Ca₂Ba₂Cu₃O_x (2223) superconducting phases, and have successfully reduced the density of impurity phases by controlling the stoichiometry and morphology of the precursor films and the thalliation conditions. In addition, a 150 mu m wide, and 1 cm long, track patterned in one of these films using standard photolithography techniques shows a T_c0 of 102 K, a J_c in excess of 10⁴ A cm^-2 at 90 K and a strong bolometric response when illuminated with an He-Ne 1 mW laser.