(Invited) Highly Reliable Metal Oxide Thin Film Transistors for Flexible Devices

Abstract

Amorphous oxide semiconductors (AOS), such as amorphous InZnO (IZO), have been widely explored as channel material for thin-film transistors (TFTs) due to its high mobility (μ) and excellent uniformity.Its solution processability allows for application to cheap and flexible electronics. To achieve cheaper manufacturing cost and large-area production, successful integration of solution-based layers is necessary. In fact, other popular solution-based conductive films, such as carbon nanotubes and polymeric materials have been previously used as electrodes. However, their conductivity is generally lower and their integration requires complex processes. Meanwhile, AOS show promising optoeletronic properties as well as good contact with oxide channels. In this work, solution-based IZO semiconductor was functionalized for electrode applications using photo-assisted treatments, namely UV and excimer laser irradiation, and was employed in an all-solution oxide TFT fabrication.IZO functionalization was achieved through either UV (λ=254 nm) irradiation for 15 to 60 mins or with additional excimer laser (λ=248 nm) irradiation in vacuum, air, or N2 at a fluence from 100 to 140 mJ cm-2. The results of X-ray photoelectron spectroscopy O 1s analysis suggests oxygen vacancy generation which effectively increases the carrier concentration in the irradiated IZO film. Moreover, IZO was crystallized from the amorphous as-deposited film after irradiation as obtained from X-ray diffraction and scanning transmission electron microscopy analyses. The laser-induced heating likely caused the IZO crystallization which provided the enhanced charge transport in the oxide film. Finally, the metal-oxide functionalization was employed in an all-solution processed oxide TFT fabrication using IZO for the channel and the electrodes, and fluorinated polysiloxane for the gate insulator. The self-aligned TFT structure that was employed, enabled the selective functionalization of the IZO gate, source, and drain electrodes. The metal oxide functionalization using UV and excimer laser irradiation yielded oxide TFTs with excellent transfer characteristics and good stability even after three months of storage in air. The all-solution processed fabrication demonstrated in this work is relevant for high throughput fabrication such as roll-to-roll processing.