Atmosphere Effect in Post-Annealing Treatments for Amorphous InGaZnO Thin-Film Transistors with SiOx Passivation Layers

We investigated the electrical performance and positive bias stress (PBS) stability of the amorphous InGaZnO thin-film transistors (a-IGZO TFTs) with SiOx passivation layers after the post-annealing treatments in different atmospheres (air, N2, O2 and vacuum). Both the chamber atmospheres and the device passivation layers proved important for the post-annealing effects on a-IGZO TFTs. For the heat treatments in O2 or air, the larger threshold voltage (VTH) and off current (IOFF), smaller field-effect mobility (μFE), and slightly better PBS stability of a-IGZO TFTs were obtained. The X-ray photoemission spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) measurement results indicated that the oxygen atoms from the ambience led to less oxygen vacancies (VO) and more oxygen-related defects in a-IGZO after the heat treatments in O2 or air. For the annealing processes in vacuum or N2, the electrical performance of the a-IGZO TFTs showed nearly no change, but their PBS stability evidently improved. After 4500 seconds’ stressing at 40 V, the VTH shift decreased to nearly 1 V. In this situation, the SiOx passivation layers were assumed to effectively prevent the oxygen diffusion, keep the VO concentration unchanged and refuse the oxygen-related defects into the a-IGZO films.

Interface scattering dominated carrier transport in hysteresis-free amorphous InGaZnO thin film transistors with high-k HfAlO gate dielectrics by atom layer deposition

In this work, we systematically investigated the carrier transport of hysteresis-free amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) incorporating high-k (HfO2)x(Al2O3)y gate dielectrics with different composition and permittivity by atomic layer deposition (ALD). A dielectric surface morphology dominated interface scattering carrier transport mechanism is demonstrated, and the effect of the dielectric polarization and the interface states on the carrier mobility is discovered in TFT devices gated by high quality dielectrics with negligible charge trap effect. Accordingly, an a-IGZO TFT gated by (HfO2)0.5(Al2O3)0.5 dielectric with the smoothest surface exhibits the best performance in terms of a preferable field-effect mobility of 18.35 cm2 V-1 s-1, a small subthreshold swing of 0.105 V decade-1, a high on/off current ratio of 4.6× 106, and excellent stability under positive bias stress.