Ultrathin Indium Tin Oxide Transistors: Interplay of Oxygen Vacancy Engineering and Dimensional Scaling Effects

Abstract

Although indium tin oxide (ITO) has been widely used as a transparent conducting oxide because of its excellent optical transparency and high electrical conductivity, the intrinsically high carrier concentration of conventional thick ITO films, arising from Sn doping and oxygen-vacancy-related donor defects, makes effective electrostatic gate modulation difficult, thereby limiting their application as switchable semiconductor channels. In this work, high-performance ultrathin ITO thin-film transistors were realized through the synergistic effects of oxygen-vacancy engineering and dimensional scaling. By precisely controlling oxygen partial the pressure during sputtering combined with post-deposition annealing, the carrier density was effectively reduced, enabling strong gate modulation in ultrathin (3–15 nm) channels with an on/off ratio up to ∼1010 and improved subthreshold characteristics. Systematic thickness scaling further reveals enhanced electrostatic control in ultrathin channels while reduced channel lengths introduce geometry-dependent transport behavior, highlighting the interplay between electrostatics, contact effects, and residual free carriers. In addition, metal–ITO interface studies using Al, Ti, Cu, and Ni reveal that the contact resistance does not follow a simple trend with the nominal metal work function, indicating the importance of metal/ITO interfacial properties in carrier injection. Among these, Ni yields the lowest contact resistance (∼1.27 Ω·mm) and a low effective Schottky barrier (∼0.144 eV), enabling efficient carrier injection. This work establishes ultrathin ITO as a scalable oxide semiconductor platform by unifying defect-controlled carrier modulation, electrostatic scaling effects, and interface-limited transport physics.