Indium and Tin Doping of Zinc Oxide Film by Cation Exchange and its Application to Low-Temperature Thin-Film Transistors

Abstract

Thin-film transistors (TFTs) based on ternary or quaternary metal oxides possess features that are advantageous for the commercialization of large-area and flexible displays. These features include high mobility, high current on-off ratio, and uniformity over large areas. However, the manufacture of TFTs mainly uses costly sputtering equipment with low throughput. Here, it is demonstrated that cation exchange is a novel, solution-based route for obtaining high-quality ternary metal oxide films from binary metal oxide films. Specifically, some Zn ions in the parent ZnO film are replaced with In or Sn ions in a solution at room temperature, while preserving the ionic framework of the parent ZnO lattice to some degree. Consequently, annealing the resulting cation-exchanged film at 250 degrees C yields an In- or a Sn-doped ZnO film, in which In or Sn acts as a substitutional donor, with its electrical properties superior to those of the parent ZnO film. With the use of these In- and Sn-doped ZnO films as channel layers, TFTs exhibit field-effect mobilities of 10.3 and 7.1 cm(2) V-1 s(-1) and turn-on voltages of -3.9 and -1.2 V, respectively, with current on-off ratios exceeding 10(8).