Progress in semiconducting oxide-based thin-film transistors for displays

Recent progress in the development of transparent thin-film transistors for integration with flexible displays is discussed. Specifically, the fabrication and properties of ZnO-based thin-film transistors on glass are described. Top-gate-type thin-film transistors with transparent n-type ZnO as the active channel layer have been fabricated via wet photolithography processing. The ZnO layers were deposited using pulsed laser deposition. A low leakage current of 10^-7 A cm^-2 was realized with amorphous HfO₂ or (Ce, Tb)MgA₁₁O₁₉ as the gate dielectric. N-channel depletion-mode operation was shown for the undoped ZnO thin-film transistors. Phosphorus-doped ZnO and (Zn, Mg)O were also utilized as channel materials in order to realize a reduction in carrier density. The current-voltage measurements demonstrate an enhancement-mode device operation for the thin-film transistors with P-doped (Zn, Mg)O as the active channel layer and HfO ₂ serving as the gate dielectric.