Technologies for Enhancing the Stability of Metal-Oxide Thin-Film Transistors

Abstract

Indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) have emerged as a promising candidate for next-generation electronics, outperforming conventional TFTs in terms of high mobility, low off-current, and optical transparency, thereby enabling applications in high-resolution displays, flexible electronics, and low-power integrated circuits. However, the reliability of IGZO TFTs remains a critical challenge, primarily due to oxygen deficiencies, susceptibility to hydrogen-induced degradation, and poor thermal stability under high-temperature conditions. Recent studies have demonstrated that fluorine (F) plasma treatment can enhance device reliability under electrical stress and non-oxidative thermal treatment. However, the correlation between the effectiveness of fluorination and the fluorination conditions has not yet been clarified. Moreover, the thermal stability of fluorinated TFTs needs to be further enhanced.

This work systematically investigates the correlation between effectiveness of fluorination and process parameters. The results reveal that that the magnitude of the improvement is enhanced by a high fluorination temperature and a post-fluorination thermal redistribution of fluorine but by a post-fluorination exposure to an oxidizing atmosphere. Notably, replacing tetrafluoromethane (CF₄) with nitrogen trifluoride (NF₃) as the fluorination precursor broadens the applicability of the process. Additionally, reducing oxygen content during IGZO sputtering enhances fluorine incorporation in IGZO channel, further enhancing the effectiveness of fluorination.

Further studies proves that the thermal stability of metal oxide (MO) TFT is strongly influenced by the atmosphere environment surrounding the active region channel, suggesting structural optimization to encapsulate the channel in oxygen-rich and H-deficient regions as a viable solution. Key strategies include storing oxygen in adjacent silicon oxide passivation (PV) layers, depositing capping layers with gas impermeable film to prevent oxygen escape and embedding oxidation-resistant conductive liners beneath source/drain electrodes to suppress the oxygen interaction between electrode and channel. A hydrogen-deficient local environment around the channel further enhances thermal reliability.

Building on these techniques, top-gate self-aligned (TG-SA) IGZO TFTs with improved thermal stability were fabricated. Sidewall spacer structure was adopted to supress the hydrogen diffusion during non-oxidative thermal treatment.

Date of Award	2025
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Man Hoi WONG (Supervisor)