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We demonstrated gate insulators (GI) fabricated by solution process with the aim of replacing traditional vacuum processed GI. We selected solution siloxane-based material due to its extremely high thermal resistance, excellent transparency, flexibility, and simple cost-effective fabrication. We made top gate TFT by depositing a siloxane gate insulator through spin-coating technique on a-IGZO. For comparison, we measured a conventional a-IGZO TFT using SiO2 as a GI for a reference. The TFTs with siloxane GI showed extremely high mobility (µ= 22±3 cm2·V-1·s-1), ultra-smooth interface (no hysteresis), and including other suitable electrical characteristics that are promising to enable the possibility to fabricate high performance all-solution processed devices in the future.

In a previous work, we reported the high field effect mobility of ZnO-doped In2O3 (IZO) thin film transistors (TFTs) irradiated by excimer laser annealing (ELA) [M. Fujii et al., Appl. Phys. Lett. 102, 122107 (2013)]. However, a deeper understanding of the effect of ELA on the IZO film characteristics based on crystallinity, carrier concentrations, and optical properties is needed to control localized carrier concentrations for fabricating self-aligned structures in the same oxide film and to adequately explain the physical characteristics. In the case of as-deposited IZO film used as the channel, a high carrier concentration due to a high density of oxygen vacancies was observed; such a film does not show the required TFT characteristics but can act as a conductive film. We achieved a decrease in the carrier concentration of IZO films by crystallization using ELA. This means that ELA can form localized conductive or semi-conductive areas on the IZO film. We confirmed that the reason for the carrier concentration decrease was the decrease of oxygen-deficient regions and film crystallization. The annealed IZO films showed nano-crystalline phase, and the temperature at the substrate was substantially less than the temperature limit for flexible films such as plastic, which is 50°C. This paves the way for the formation of self-aligned structures and separately formed conductive and semi-conductive regions in the same oxide film.

Highly reliable amorphous InGaZnO (a-IGZO) (In:Ga:Zn:O  =  2:2:1:7) thin-film transistors (TFTs) were fabricated with 25 nm-thick Al2O3 passivation deposited by atomic layer deposition (ALD) using dimethylaluminum hydride (DMAH). Al2O3 passivation deposited at various temperatures was studied to determine its effect on TFT behavior following gate bias stress and humidity exposure. The Al2O3-passivated a-IGZO TFTs demonstrated an on-off current ratio (Ion/Ioff) of ~108 and linear mobility (µ) of 9 to 13 cm2 V−1 s−1. An optimum ALD temperature of 200 °C was demonstrated to result in Al2O3-passivated a-IGZO TFTs with very small on-voltage shifts of 0.3 V and  −2.7 V against positive bias stress and negative bias illumination stress (NBIS) after 10 000 s of stress time. Furthermore, negligible degradation was observed after humidity exposure. The results of x-ray photoelectron spectroscopic analysis of the O 1s spectra showed the highest peak area ratio for metal–oxygen (M–O) bonding and lowest metal–oxygen vacancy (M–Vo) bonding, relating to the least amount of trap sites both in the bulk region of a-IGZO and near the interface of Al2O3/a-IGZO, for the device passivated at 200 °C. It was also found that at a low deposition temperature (⩽100 °C), low-density Al2O3 was formed with high carbon contamination and hydrogen while at a high deposition temperature (⩾300 °C), high hydrogen concentration was also present in high-density Al2O3. The hydrogen incorporation from Al2O3 passivation to a-IGZO channel creates bulk defects and trap sites as well as in the interface of a-IGZO and SiO2 gate insulator. At 200 °C, high quality Al2O3 passivation was achieved with high density and reduced impurities leading to improved device reliability. These results can be applied to long term sustained device operations which are reliable against different stresses. [ABSTRACT FROM AUTHOR]

We demonstrate the rapid (<100 ns) activation and enhancement of solution-processed InZnO thin-film transistors (TFT) via a photo-assisted process: excimer laser annealing (ELA). A single shot is sufficient to enhance mobility from 0.19 cm2 V−1 s−1 to 3.91 cm2 V−1 s−1. Through multiphysics simulation, we confirmed that the process is instantaneous (<100 ns) and induces low substrate temperature suitable for flexible substrates. Analysis of optical properties, elemental concentration, and bonding changes after ELA revealed an improved metal-oxide formation and effective reduction of precursor-related impurities and oxygen vacancy traps. These demonstrate ELA’s potential for high-throughput fabrication of solution-processed devices for large-area, transparent, and flexible electronics. [ABSTRACT FROM AUTHOR]

Photon emission and the electrical characteristics of a InGaZnO (IGZO) thin-film transistor (TFT) were evaluated to clarify the existence of hot carriers and their effects. The photon emission was observed from the drain edge of the IGZO-TFT and the capacitance–voltage characteristics indicated that a potential barrier was formed at the drain region when the device is driven by high drain voltage of 30 V. Based on these results, the photon emission phenomenon from the IGZO-TFT was induced by hot carriers that should be considered as a significant degradation mode for a high-performance oxide semiconductor device. [ABSTRACT FROM AUTHOR]

Thin-film transistors (TFTs) using metal oxide semiconductors are very promising as driving elements of next-generation displays, and their development is rapidly progressing. However, compared to conventional Si TFTs, they exhibit numerous problems with reliability. In this paper, we outline the observations of various degradation phenomena against electrical bias stress under DC and AC voltage, discuss the degradation mechanism, introduce gate insulation film and protective film which contribute to the improvement of reliability, and propose a reliability evaluation technique using an IR microscope. [ABSTRACT FROM AUTHOR]

This paper presents a low-temperature solution-processed passivation material based on polysilsesquioxane (PSQ) which greatly improves electrical performance and stability of solution-processed amorphous InZnO (a-IZO) thin-film transistors (TFTs). PSQ-passivated TFTs exhibited maximum mobilities of 6.02 cm2 V−1 s−1 with the smallest threshold voltage shift of 2.8 V after positive bias stress test. We showed that hydrogen-related ions from PSQ passivation help passivate oxygen vacancies, thus improving the percolation path in a-IZO channel. Moreover, PSQ-passivated TFTs showed minimal change after being subjected to humidity stress. These results demonstrate the ability of low-temperature PSQ passivation as an effective barrier against atmospheric effects. [ABSTRACT FROM AUTHOR]

Electric double-layer transistors (EDLTs) are capable of achieving ultra-high carrier density and very low operating voltages. However, chemical reactions cause structural change at the semiconductor–insulator interface resulting in unstable device operation and reduced device lifetime. In this work we propose a method of depositing a 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FDTS) layer which acts as a barrier between the semiconductor layer and the ionic liquid insulator. Our work shows that the effects of adding FDTS film are isolation of the chemical reaction and reduction of damage to the amorphous InGaZnO channel, thus achieving the effect of increasing device lifetime and stability. [ABSTRACT FROM AUTHOR]

TlZnSnO films, fabricated by sputtering with TlZnSnO targets composed of TlZnSnO powder, which was prepared via two-stage calcination, were analyzed. This study reports the first trial of TlZnSnO film preparation, and its optical and electrical properties. Tl atom concentrations of 0.9–1.36 at.% in the TlZnSnO films changed the bandgap between 2.83 and 3.07 eV. The obtained TlZnSnO ionization potential of 5.57–5.9 eV was slightly smaller than that of amorphous InGaZnO (a-IGZO). We also found that the conduction band was located approximately around 3 eV or lower beneath the vacuum level for each examined film; and that a deep density of state (DOS) exists near the valence band. A similar subgap DOS to that of a-IGZO existed even in TlZnSnO. However, the bandgap (2.83–3.07 eV) and donor level (31 meV) of TlZnSnO are smaller than those of a-IGZO. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) of Al2O3 using dimethylaluminum hydride (DMAH) was demonstrated as an effective passivation for amorphous InGaZnO thin-film transistors (TFTs). Compared with the most commonly used precursor, trimethylaluminum, TFTs fabricated with DMAH showed improved stability, resulting from the lower amount of oxygen vacancies, and hence fewer trap sites, as shown by X-ray photoelectron spectroscopy (XPS) depth profiling analysis. We found that prolonged plasma exposure during ALD can eliminate the hump phenomenon, which is only present for DMAH. The higher Al2O3 deposition rate when using DMAH is in line with the requirements of emerging techniques, such as spatial ALD, for improving fabrication throughput. [ABSTRACT FROM AUTHOR]

Fabrication process conditions of a passivation (PV) layer correlated with stress stabilities of amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs). In etch-stop layer (ESL)-TFTs, by inserting a Si-based resin between SiNx and SiOx PV layers, the peak intensity in the photoinduced transient spectroscopy (PITS) spectrum was notably reduced. This suggested the suppression of hydrogen incorporation into a-IGZO, which led to the improvement of stability under negative bias thermal illumination stress (NBTIS). In contrast, the hydrogen-related defects in the a-IGZO were easily formed by the back-channel etch (BCE) process. Furthermore, it was found that, under NBTIS, the transfer curves of the BCE-TFTs shifted in parallel owing to the positive fixed charge located in the back channel of the a-IGZO TFTs. The hump-shaped shift increased with stress time. This is because hydrogen atoms located at the back-channel surfaces of the a-IGZO and/or PV layers were incorporated into the channel region of the BCE-TFTs and induced the hydrogen-related defects. [ABSTRACT FROM AUTHOR]

We demonstrate the use of excimer laser annealing (ELA) as a low temperature annealing alternative to anneal amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) passivated by a solution-processed hybrid passivation layer. Usually, a-IGZO is annealed using thermal annealing at high temperatures of up to 400 °C. As an alternative to high temperature thermal annealing, two types of ELA, XeCl (308 nm) and KrF (248 nm) ELA, are introduced. Both ELA types enhanced the electrical characteristics of a-IGZO TFTs leading to a mobility improvement of ~13 cm2 V−1 s−1 and small threshold voltage which varied from ~0–3 V. Furthermore, two-dimensional heat simulation using COMSOL Multiphysics was used to identify possible degradation sites, analyse laser heat localization, and confirm that the substrate temperature is below 50 °C. The two-dimensional heat simulation showed that the substrate temperature remained at very low temperatures, less than 30 °C, during ELA. This implies that any flexible material can be used as the substrate. These results demonstrate the large potential of ELA as a low temperature annealing alternative for already-passivated a-IGZO TFTs. [ABSTRACT FROM AUTHOR]