We report solution-processed, amorphous indium-gallium-zinc-oxide-based (a-IGZO-based) thin-film transistors (TFTs). Our proposed solution-processed a-IGZO films, using a simple spin-coating method, were formed through nitrate ligand-based metal complexes, and they were annealed at low temperature (250 °C) to achieve high-quality oxide films and devices. We investigated solution-processed a-IGZO TFTs with various thicknesses, ranging from 4 to 16 nm. The 4 nm-thick TFT films had smooth morphology and high-density, and they exhibited excellent performance, i.e. a high saturation mobility of 7.73 ± 0.44 cm 2 V −1 s −1 , a sub-threshold swing of 0.27 V dec −1 , an on/off ratio of ~10 8 , and a low threshold voltage of 3.10 ± 0.30 V. However, the performance of the TFTs degraded as the film thickness was increased. We further performed positive and negative bias stress tests to examine their electrical stability, and it was noted that the operating behavior of the devices was highly stable. Despite a small number of free charges, the high performance of the ultrathin a-IGZO TFTs was attributed to the small effect of the thickness of the channel, low bulk resistance, the quality of the a-IGZO/SiO 2 interface, and high film density.

A top-gate oxide thin-film transistor (TFT) with all spin-on-glass (SOG) insulators was developed. The SOG is based on methyl siloxane and was used for the buffer layer, gate insulator, and interlayer dielectric instead of a vacuum process. The SOG was diluted with ethanol, and a small amount of hydrogen peroxide was added. The diluted SOG was applied to top-gate amorphous indium–gallium–zinc-oxide TFTs, and the effects of the dilution and the hydrogen peroxide added were investigated. The TFTs with the optimized SOG insulators showed a mobility of 7.1 cm2/(V·s), a threshold voltage of 0.5 V, a subthreshold slope of 0.1 V/dec, and an on/off current ratio of 3.6 × 107.

A vertical oxide thin-film transistor was developed with interfacial oxidation for low voltage operation. The gate metal was used as a spacer for the definition of the transistor’s channel as well as the gate electrode. After definition of the vertical side wall, an IGZO (In-Ga-Zn Oxide) layer was deposited, followed by the interfacial oxidation to form a thin gate insulator. Ta was used for the gate material due to the low Gibbs free energy and high dielectric constant of tantalum oxide. A 15 nm tantalum oxide layer was obtained by the interfacial oxidation of Ta at 400 °C under oxygen atmosphere. The thin gate oxide made it possible to operate the transistor under 1 V. The low operation voltage enables low power consumption, which is essential for mobile application.

A solution-based spin-on glass (SOG) was applied to the gate insulator of an oxide thin-film transistor (TFT). The curing atmosphere of the SOG was investigated to enhance the performance of the self-aligned top-gate In-Ga-Zn-O (IGZO) TFT. After the SOG layer was formed on an IGZO active layer, curing was performed under N 2 , air, and O 2 atmospheres. The curing under an N 2 atmosphere resulted in the best device characteristics for the IGZO TFT. After curing, the SOG films were investigated via atomic force microscopy, secondary ion mass spectroscopy, Fourier transform infrared spectroscopy, and capacitance measurement. The results showed that the N 2 pileup at the back surface of the SOG is the main reason for the enhanced performance of the TFT after curing under an N 2 atmosphere.

In this paper, we proposed the gate driver circuit with a-IGZO TFTs for stretchable display. In addition, a proposed circuit used only two a-IGZO TFTs and it did not have the floating node. Developed circuit shows the stable output signal even if the characteristics of the TFT were changed under the strain.