Amorphous metal oxide thin-film transistors (TFTs) are fabricated using InOx-based semiconductors doped with TiO2, WO3, or SiO2. Even at low-dopant densities, the electrical properties of the film strongly depend on the dopant used. We found that this dependence could be reasonably explained by differences in the bond-dissociation energy of the dopants. By incorporating a dopant with a higher bond-dissociation energy, the film became less sensitive to the partial pressure of oxygen used during sputtering and remained electrically stable upon thermal annealing. Thus, choosing a dopant with an appropriate bond-dissociation energy is important when fabricating stable metal-oxide TFTs for flat-panel displays.

Thin-film transistors (TFTs) with a high stability and a high field-effect mobility have been achieved using W-doped indium oxide semiconductors in a low-temperature process (∼150 °C). By incorporating WO₃ into indium oxide, TFTs that were highly stable under a negative bias stress were reproducibly achieved without high-temperature annealing, and the degradation of the field-effect mobility was not pronounced. This may be due to the efficient suppression of the excess oxygen vacancies in the film by the high dissociation energy of the bond between oxygen and W atoms and to the different charge states of W ions.

Incorporating SiO₂ into amorphous In₂O₃-based thin films is found to suppress the formation of unstable oxygen vacancies. The SiO₂ incorporated thin film transistors exhibited reliable device characteristics after being annealed at 250 °C. Increasing the SiO₂ content of the sputtering target decreased the sensitivity of the subthreshold swing and turn-on voltage of the device to the sputtering conditions used to deposit the amorphous oxide, making them more stable against electrical and thermal stresses. The increased activation energy of the charge carriers in the current off region indicated a smaller density of states at the conduction-band tail, supporting stable transistor operations.