Variation of oxygen deficiency in solution-processed ultra-thin zinc-tin oxide films to their transistor characteristics

Ultra-thin zinc-tin oxide (ZTO) films (∼7 nm thick) with different Sn/(Sn+Zn) molar ratios, fabricated by using a solution process in combination of spin coating method, are applied as channel layers in thin film transistors (TFTs) with a bottom-gate top-contact structure. With regard to material characteristics, oxygen deficiency in ZTO films can be substantially decreased with the addition of different Sn contents. The non-Sn added ZnO TFT cannot be turned on whereas the Sn added ZTO channel layers perform TFT characteristics adequately, indicating the necessity of reducing oxygen deficiency by introducing Sn during the solution synthesizing process. With a Sn/(Sn+Zn) molar ratio of 0.5, the ZTO TFT exhibits the best field-effect mobility of ∼2.0 cm²/V s and a large on/off current ratio of ∼10⁸. The electrical characteristics of ZTO TFTs are explored and correlated to the levels of oxygen deficiency associated with various Sn contents.