Crystallinity and adhesiveness improvements of Ag thin films by Bi- and Sb-assisted growth

Abstract

Ag thin films are used in a variety of electrical devices, but they easily condense owing to the low cohesive energy of Ag. In this study, Bi- and Sb-assisted growth techniques were utilized to improve the stability of Ag thin films. Thin films of Ag, Bi-doped Ag, and Sb-doped Ag were deposited on polyimide (PI) films at 160 and 320 °C by radio frequency magnetron sputtering. The thin-film orientation and strain were determined by analyzing the X-ray diffraction patterns. In addition, the adhesiveness between the thin films and PI substrates was evaluated by immersion tests. The [111] growth of the Ag thin films was assisted by Bi at 160 °C and by Sb at 320 °C, where the (111) orientation possesses the lowest surface energy for the face-centered cubic structure of the Ag thin films. The strain present in the PI film was not applied to the grown thin films. Doping with Bi or Sb decreased the thin-film strain and prevented the detachment of the Ag thin film from the PI film in pH 9 buffer, with the exception of the Sb-doped Ag thin film grown at 160 °C, which exhibited non-uniform growth. Thus, Bi or Sb doping can suppress the condensation of Ag thin films by enhancing their (111) orientation and adhesiveness to the substrate. The obtained results indicate that Bi- and Sb-assisted growth techniques can stabilize Ag thin films and improve the reliability of devices based on these films.