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

Abstract

Superconducting Tl-Ca-Ba-CuO thin films less than 1 pm thick have been prepared on Y-stabilized ZrO, (100). MgO (100). and SrTiO, (100) substrates using thermal evaporation and a two-step annealing process involving the growth of BaCuO, films followed by exsilu crystallization and thalliation under thallium oxide vapours. We have been able to fabricate reasonably uniform films of t h e TI,Ca, Ba,Cu,O. (2122) and Ti,Ca,Ba,Cu,O, (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 pm wide, and 1 cm long, track patterned in one of these films using standard photolithography techniques shows a T,, of 102 K. a J, in excess of IO4 A cm-' at 90 K and a strong bolometric response when illuminated with an He-Ne 1 mW laser

Process optimization for the fabrication of Tl2Ba2Ca2Cu3O10 thin films

“…Both BaCaCuO and TlBaCaCuO precursor films have been used, and a variety of methods have been used in their preparation, including sputtering, 19-28 laser ablation, 29,30 evaporation, [31][32][33] and spray pyrolysis. These films have been prepared exclusively using ex situ postdeposition thallination processes, during which a precursor film is converted to the crystalline Tl 2 Ba 2 Ca 2 Cu 3 O 10 phase in the presence of a thallous oxide overpressure.…”

“…These films have been prepared exclusively using ex situ postdeposition thallination processes, during which a precursor film is converted to the crystalline Tl 2 Ba 2 Ca 2 Cu 3 O 10 phase in the presence of a thallous oxide overpressure. 19,20,29,31,[33][34][35] A few studies have used a thallium oxide source held at a lower temperature than that of the film to maintain a thallous oxide overpressure. [34][35][36] The thallination step is most often carried out in the presence of a TlBaCaCuO powder, within a sealed gold pouch or ceramic ampoule, 21,[24][25][26][27][28] or within a closed, but unsealed, platinum or ceramic container.…”

Characterization of films prepared by laser ablation of precursor targets andex situthalliation

“…Thallium-based thin superconducting films are considered to be very promising materials for the fabrication of various passive microelectronic devices (bandfilters, resonators, etc) due to their high critical temperature, T c , high critical current density, j c , and particularly low surface impedance at 77 K [1]. These features have been the motivation for the exploration of various methods of film fabrication such as RF sputtering [2,3], e-beam evaporation [4], thermal evaporation [5] and laser ablation [6,7]. The last method seems to be the most attractive, in that it enables one to deposit a ∼ 0.3-0.5 µm thick film in a short time (∼ 10-15 min) which is at least a factor of 10 shorter than the time needed for other methods (for example RF sputtering).…”

Preparation and properties of precursor Ba–Ca–Cu–(O, F) thin films deposited from fluorides for superconducting Tl- and Hg-based films

“…We did not detect any peaks belonging to carbides like BaCO 3 which may appear as a consequence of an interaction of precursor films with the surrounding atmosphere. Lai et al 14 have prepared Ba-Ca-Cu-O precursor films in a two-step process where asevaporated Cu-BaF 2 films were preannealed at 845 °C for 3-5 h in pure oxygen in the presence of water vapour as to form stable BaCaO 2 phase and to eliminate the formation of CaCu 2 O 3 phase which hinders the growth of the superconducting phase during thallination.…”