Effect of Post-Thermal Annealing of Thin-Film Transistors with ZnO Channel Layer Fabricated by Atomic Layer Deposition

We investigated zinc oxide (ZnO) thin films fabricated by atomic layer deposition (ALD) for their application in thin-film transistors (TFTs). The fabricated TFTs were annealed at various temperatures in various ambient gases. The characteristics of TFTs annealed in oxygen ambient at the temperature of up to 400 °C indicated improvements with no degradation of subthreshold swing or large shift in threshold voltage. From the annealing temperature dependences of transfer characteristics and X-ray diffraction patterns, we found that the improvements in electrical characteristics are attributed to the crystalline modification of ZnO films. The TFTs annealed at 400 °C in O2ambient indicate improved stability against the bias stress. Secondary ion mass spectrometry analysis revealed a marked decrease in the hydrogen concentration of the ZnO channel layer after the annealing at 400 °C.