Correlation among Process, Microstructure/Stoichiometry, and Transport in Spin-Coated Al-Doped ZnO Thin-Film Transistors Subjected to Annealing-Induced Electrical Performance Enhancement

Abstract

Spin-coated oxide semiconductors enable low-cost, large-area manufacturing. Nevertheless, the quantitative correlation among the postannealing conditions, microstructure, stoichiometry, and charge transport remains unclear. To clarify these relationships, we postannealed Al-doped ZnO (AZO) thin films and analyzed their microstructures and chemistries by SEM, XRD, TEM, and XPS. Plane-view SEM revealed ∼150 nm island-like secondary aggregates, whereas XRD did not resolve the distinct AZO diffraction peaks. Cross-sectional TEM revealed primary nanoparticles that coarsened upon annealing. XPS showed increased intensity of the O 1s component near 531 eV, associated with oxygen-deficient states, indicating enhanced oxygen nonstoichiometry. These microstructural and stoichiometric changes were correlated with device behavior. Postannealing increased the field-effect mobility and on/off ratio of the AZO thin-film transistors (TFTs) by 302.4% and 602.3%, respectively. The mobility scaled linearly with the mean primary particle size within the annealing conditions investigated in this study (R2 = 0.986). This study provides an experimentally supported relationship among process, microstructure/stoichiometry, and transport under modest thermal budgets and offers practical guidelines for optimizing solution-combustion oxide TFTs.