Effects of Indium Composition Ratio on Electrical Stability of Top-gate Self-aligned Coplanar IGZO TFTs under Self-heating Stress Conditions

We demonstrated that the indium composition ratio in the channel layer significantly affects the electrical stability of top-gate self-aligned (TG SA) coplanar structure indium-gallium-zinc oxide (IGZO) thin-film transistors (TFTs) under self-heating stress (SHS) conditions. The transfer curves of the In-poor IGZO TFT continuously shifted in the positive direction with extended stress time, without a significant change in the subthreshold swing (SS) and field-effect mobility (μFE) values during SHS application. In contrast, the transfer curve of the In-rich IGZO TFT shifted in the negative direction until the SHS time reaches 1200 s, after which it shifted in the positive direction with extended stress time. Besides, SS and μFE values continuously increased as the SHS time increased in the In-rich IGZO TFTs. The unusual behavior of the TG SA coplanar In-rich IGZO TFT during SHS is mainly attributed to the more pronounced diffusion of hydrogen (H) atoms from the n+-IGZO source/drain extension region to the IGZO channel region in the In-rich IGZO than in the In-poor IGZO. The H atoms diffused into the IGZO channel layer act as either shallow donors or deep acceptors, depending on their concentration and environmental conditions, thus causing the abnormal behavior of IGZO TFTs during SHS.