Self-Aligned Amorphous Indium-Tin-Zinc-Oxide Thin Film Transistors on Polyimide Foil

• Published in: ECS journal of solid state science and technology 2018-01, Vol.7 (4), p.P185-P191
• Main Authors: Upadhyay, Rishabh, Steudel, Soeren, Hung, Mai-Phi, Mandal, Akhilesh Kumar, Catthoor, Francky, Nag, Manoj
• Format: Article
• Language: English
• ISSN: 2162-8769; 2162-8769; 2162-8777
• DOI: 10.1149/2.0141804jss

In this work, we report on high-performance coplanar self-aligned (SA) amorphous-Indium-Tin-Zinc-Oxide (a-ITZO) thin-film transistors (TFTs) on flexible polyimide substrate. The a-ITZO films are first optimized with respect to the oxygen ratio, thickness and final anneal conditions with common-gate TFTs structure on Si/SiO2 substrate. Optimized TFTs show mobility (μlin) between 20.0-25.0 cm2/(V.s). Material characterization revealed some degree of order compared to a truly amorphous film like a-IGZO but no grain boundaries or crystalline domains were observed. The a-ITZO films were integrated in coplanar SA TFT architecture on polyimide using hydrogen rich plasma (SiH4 based chemistry) as dopant for the source/drain (S/D) regions resulting in field-effect mobility (μFE) of 27.0 cm2/ (V.s), sub-threshold slope (SS−1) of 0.40 V/decade and ION /IOFF ratio of >108. The threshold voltage shifts of the TFTs under both positive and negative gate bias stress of 1MV/cm for 104 seconds were less than 1.5 V. We have also investigated the applicability of the SA a-ITZO TFTs in logic circuitry such as 19-stage ring-oscillators (ROs).