Effect of substrate temperature and RF biasing on the composition of sputtered Bi-based superconducting thin films

The variation of the composition, as a function of the substrate temperature and RF biasing, in single-target sputtered Bi-Sr-Ca-Cu-O, Bi-Pb-Sr-Ca-Cu-O and Bi-Pb-Sb-Sr-Ca-Cu-O thin films has been studied, because of the influence on the formation of high-Tc superconducting phases. It was found that the atomic concentration of Sr in the sputter-deposited films matched well with that in the target over a wide range of substrate temperatures and RF biasing voltages. The relative concentrations of Bi, Pb, and O decreased with an increase in the substrate temperature and RF biasing. Ca, Cu, and Sb, concentrations increased above substrate temperatures of 600 degrees C. Relative concentrations of all the constituents except Pb varied approximately within a factor three, with substrate biasing in conjunction with RF biasing. The presence of Pb has been found to be beneficial to the formation of the 110-K high-temperature phase. However, it is not a essential element. The concentrations of Sb in the film is easy to control. Its role in the growth of high-Tc phases is questionable. Hot-pressed targets prepared from presintered and chemically reacted oxide mixtures resulted in better control of the composition, and better phase formation and oxygenation. The results show that it is possible to empirically adjust the concentrations of the oxides of Bi, Sr, Ca, and Cu in the target, in order to obtain the desired compositions in the thin films