Atmosphere Effect in Post-Annealing Treatments for Amorphous InGaZnO Thin-Film Transistors with SiO(x) Passivation Layers

We investigated the electrical performance and positive bias stress (PBS) stability of the amorphous InGaZnO thin-film transistors (a-IGZO TFTs) with SiO(x) passivation layers after the post-annealing treatments in different atmospheres (air, N(2), O(2) 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 O(2) or air, the larger threshold voltage (V(TH)) and off current (I(OFF)), smaller field-effect mobility (μ(FE)), 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 (V(O)) and more oxygen-related defects in a-IGZO after the heat treatments in O(2) or air. For the annealing processes in vacuum or N(2), 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 V(TH) shift decreased to nearly 1 V. In this situation, the SiO(x) passivation layers were assumed to effectively prevent the oxygen diffusion, keep the V(O) concentration unchanged and refuse the oxygen-related defects into the a-IGZO films.