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 °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 cm2 V−1 s−1 and turn‐on voltages of −3.9 and −1.2 V, respectively, with current on–off ratios exceeding 108.

The influence of annealing atmosphere on sputtered indium oxide thin-film transistors

“…In addition, oxygen bonds in O-H/C-O groups are considered to generate acceptor-like states near the CB edge and enhance electron trapping during positive bias stress (PBS) applications [20]. Therefore, multiple attempts have been made to modulate oxygen-related species in the active channel layer such as multi-cation doping [21,22], changing the sputtering gas flow [23], annealing treatment [24], plasma treatment [25], or their combination [26,27]. One of the effective routines for realizing TFTs with good performance is the deposition of OS channel layers with high resistivity, followed by a postdeposition annealing treatment.…”

Investigation on Atomic Bonding Structure of Solution-Processed Indium-Zinc-Oxide Semiconductors According to Doped Indium Content and Its Effects on the Transistor Performance

“…Among them, in the studies focusing on the atomic composition ratio, the field-effect mobilities in the range 0.5–10.0 cm·V −1 s −1 were controlled by varying the ratio of In:Zn or In:Zn:Ga, and the thickness, roughness, and crystallinity of the semiconductor film were investigated relative to the atomic ratio [ 14 , 15 , 16 ]. Furthermore, a field-effect mobility of over 10 cm·V −1 s −1 was demonstrated using various dopant materials [ 17 , 18 , 19 , 20 ], and a mobility improvement of approximately ten times was achieved by applying chemical treatment or post-treatment [ 21 , 22 ]. In certain cases, the electrical characteristics of the TFT were significantly enhanced via the passivation process [ 23 ].…”