  Amorphous oxide semiconductors, especially indium oxide-based (InOx)
thin-films, have been major candidates for high mobility with easy-to-use
device processability. As one of the dopants in InOx semiconductors, we
proposed Si to design a thin-film transistor (TFT) channel. Because the
suppression of unstable oxygen vacancies in InOx is crucial to maintaining the
semiconducting behavior, Si was selected as a strong oxygen binder that is
reasonably available for large production. In this review, we focus on the
overall properties observed in Si-incorporated amorphous InOx TFTs in terms of
bond-dissociation energy, Gibbs free energy, Si-concentration dependence of TFT
properties, carrier transport mechanism, and bias stress instability. In
comparing low and high doping densities, we found that the activation energy
and density of states decreased at a high Si concentration in InOx TFTs,
implying that the trap density was reduced. As a result, stable operation under
bias stresses could be realized. Furthermore, the inverse Meyer-Neldel rule was
observed in the highly Si-doped InOx TFT, indicating reasonable ohmic contact.
Based on our fundamental knowledge of the Si-doped InOx film, we developed a
high-mobility bilayer TFT with a homogeneous stacked channel that was different
from a TFT with an etch stop layer structure. The TFT showed remarkably stable
operation. With simple element components based on InOx, it is possible to
systematically discuss vacancy engineering in terms of conduction properties.
