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High-k amorphous SrTa2O6 (STA) thin films were successfully deposited by rf magnetron sputtering for gate insulators in thin-film transistor (TFT). Practical STA thin films with high dielectric constant of 41.8, wide band gap of 4.58 eV, and low leakage current of ~10−8 A/cm2 were obtained through by optimal sputtering condition. The TFTs with amorphous InGaZnO (IGZO) as a channel and STA as a gate insulator were fabricated and investigated for thinning effects of gate insulator on transfer characteristic. The IGZO-TFT with 70-nm-thick STA achieved high performance switching properties; (mobility of 14.9 cm2/(V·s), threshold voltage of 0.6 V, sub-threshold swing of 111 mV/decade, and on/off ratio of 1.0 × 1010). These characteristics are due to the large gate capacitance of 4.6 × 10−7 F/cm2 and low gate leakage current from use of STA.

Self-heating degradation in semiconductor devices generated by driving voltage is a serious problem in the development of highly reliable products. This letter focuses on oxide semiconductors, as a representative of flexible devices on which thermal accumulation on the substrate is critical. We propose a heat-suppressing thin-film transistor (TFT) structure to improve the reliability of transparent amorphous oxide semiconductor TFTs. Findings from this letter indicate that a structure with a curved line, such as a Corbino disk, is effective for suppressing self-heating. Based on these results, we suggest a U-shaped TFT as a heat-suppressing structure and demonstrate its device simulation and thermal analysis.

Low temperature process is required to fabricate high performance amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) on plastic substrates for flexible display applications. In addition, high-k material which allows higher mobility, higher drain current and lower threshold voltage while facilitating miniaturization, is poised to replace conventional SiO 2 gate insulators in TFTs. Therefore, hybrid material containing high-k BaTiO 3 nanoparticles and transparent Poly-siloxane (Poly-SX) were used as gate insulator in a-IGZO TFTs. Opting for a hybrid material instead of only a BaTiO 3 film enables lowering of process temperatures. This paper presents the performance of a-IGZO TFTs with solution processed hybrid gate insulators at different BaTiO 3 /Poly-SX ratios deposited at a lower temperature (300°C). The device shows a high mobility of 30.17 cm2/Vs, low threshold voltage of 0.4 V, and leakage current density of ~10−8 A/cm2.

Thermal reaction between thallium oxide (Tl2O3) and zinc oxide (ZnO), tin oxide (SnO2) or indium oxide (In2O3) annealed at 600 °C for 18 h in the air atmosphere was investigated. From XRD results of 600 °C annealed samples, Tl2O3 had the biggest reactivity compared with ZnO. The EDX results suggest the mechanism in which the thallium atoms scattered and attached uniformly only on ZnO particles. We also analyzed XPS data to compare O 1s bond and Tl 4f bond of as-mixed samples with that of annealed samples, and found that Zn and Sn can contribute in improving Tl and O bonding stability. However, the affinity of In for Tl is weaker than that of Zn or Sn. Finally, we prepared the samples mixed with ZnO, SnO2, and Tl2O3 powder and the samples mixed with Zn2SnO4 and Tl2O3 powder annealed at 600 °C for 18 h. Results show that Zn2SnO4 has the same or more reactivity than SnO2 and ZnO mixed particle despite of the more stable and sufficient dispersion of Zn and Sn atoms. More stable TlSnZnO can be fabricated from Zn2SnO4 + Tl2O3 powder by suitable thermal processes. It is expected that TlSnZnO sputtering target can be fabricated by suitable calcination.

The interaction between ambient environment or the adsorption-desorption of oxygen and water molecules at the back channel of bottom gate amorphous InZnO (a-IZO) thin-film transistors (TFTs) is one of the biggest issues that greatly affects the performance and reliability of TFTs. The issue can be overcome by depositing a passivation at the back channel as a protection barrier. This paper presents the performance of solution processed a-IZO TFTs incorporated with different types of Polysilsesquioxane (PSQ) passivation layers fabricated at low temperatures of 180 °C. A clear reliability enhancement is observed by using the low temperature PSQ which reduced the very high threshold voltage shift ( $V_{th}$ ) of 16.0 V after positive bias stress (PBS) of unpassivated a-IZO TFT to a low $V_{th}$ of 3.1 V after passivation.

We investigated the effects of the passivation layer on the characteristics of amorphous InGaZnO4 thin-film transistors (a-InGaZnO TFTs) by comparing AlOx film by thermal atomic layer deposition (TALD-AlOx) with SiOx film by plasma enhanced chemical vapor deposition (PECVD-SiOx). The PECVD-SiOx TFTs before and after final annealing exhibited conductive and hump characteristics, respectively. In contrast, both TALD-AlOx TFTs before and after final annealing exhibited enhancement characteristics. From secondary ion mass spectroscopy analysis, we found that TALD-AlOx effectively suppresses H injection into the underneath of the a-InGaZnO layer compared with PECVD-SiOx. We believe such suppression of H injection leads to the enhancement characteristics of TALD-AlOx TFTs. On the other hand, the conductive and hump characteristics of PECVD-SiOx TFTs may be attributed to a higher concentration of H injected into the a-InGaZnO layer and ion bombardment due to PECVD. From these results, we argue that plasma-free TALD-AlOx is effective for achieving good characteristics in a-InGaZnO TFTs. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0231507jss] All rights reserved.

For flexible display applications, high performance amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs) fabricated by low temperature process are required. Moreover, high dielectric constant (high-k) material which enables higher mobility and lower threshold voltage while minimizing the device size are excellent candidates to replace SiO2 gate insulators in conventional oxide semiconductor TFTs. Therefore, nanocomposite material containing high-k BaTiO3 nanoparticles and transparent poly-siloxane (PSX) hybrid polymer were deposited as gate insulator in a-IGZO TFTs to facilitate the reduction of process temperature due to the high temperature requirement (>650 oC) of BaTiO3. This paper presents the performance and analysis of a-IGZO TFTs with high-hybrid gate insulators at different ratios of BaTiO3/PSX deposited by solution process at a lower temperature (300 oC). The TFT shows a high mobility of 35.59 cm2 V−1 s−1, low threshold voltage of 0.4 V, and gate leakage current of ~10−10 A.

We demonstrate the rapid (

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.

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.

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.

Amorphous In-Ga-Zn-O thin-film transistors (a-IGZO TFTs) have attracted considerable attention as an alternative device for conventional amorphous silicon (a-Si) TFTs. The features of this material are a low fabrication temperature less than 200 ◦ C, and preferable electronic properties such as higher field-effect mobility and lower threshold voltage (Vth) compared with those of a-Si TFTs. Such desirable performances also enable us to design peripheral circuits for displays. Furthermore, a-IGZO TFTs are regarded as a prospective material for “transparent electronics”, because of their wide bandgap of ∼3.2 eV. 1‐4 On the other hand, several papers have reported that aIGZO TFTs showed poor stability against electrical stresses. 5‐7 Since reliability is an issue for the realization of next-generation displays utilizing oxide semiconductors in transparent electronics, a deeper understanding of a-IGZO and its problems are necessary. The influence of hydrogen concentration in silicon nitride (SiNx) gate insulators (GIs) on the electrical stability of a-IGZO TFTs has been actively discussed. 8‐10 Lee et al. reported that the hydrogen in SiNx film strongly induced threshold voltage shift (�V th) due to the generation of shallow charge-trapping sites for electrons. 11 Their results lead us to expect that lower hydrogen content in the gate insulator will provide quite stable TFTs. In this study, we propose a fluorinated SiNx film utilizing SiF4 and N2 as source gasses unlike conventional film fabricated with SiH4/NH3 and investigated the electrical properties of a-IGZO TFT by applying positive biased stress (PBS). In order to discuss effect on reliability of hydrogen and fluorine in the GIs, we prepared several kindsofSiNx filmswithcontrollingtheconcentrationofhydrogenand fluorine. Thermally-oxidized SiO2 gate insulator was also evaluated for comparison.

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.

Degradation of Ga2O3–In2O3–ZnO (GIZO) thin-film transistors (TFTs), which are promising for driving circuits of next-generation displays, was studied. We found a degradation mode that was not observed in silicon TFTs. A parallel shift without any change of the transfer curve was observed under gate voltage stress. Judging from the bias voltage dependences we confirmed that the mode was mainly dominated by a vertical electric field. Thermal distribution was measured to analysis the degradation mechanism. Joule heating caused by drain current was observed; however, a marked acceleration of degradation by drain bias was not found. Therefore, we concluded that Joule heating did not accelerate degradation. Recovery of electrical properties independent of stress voltage were observed.

The use of indium–gallium–zinc oxide (IGZO) has paved the way for high-resolution uniform displays or integrated circuits with transparent and flexible devices. However, achieving highly reliable devices that use IGZO for low-temperature processes remains a technological challenge. We propose the use of IGZO thin-film transistors (TFTs) with an ionic-liquid gate dielectric in order to achieve high-density carrier-accumulated IGZO TFTs with high reliability and we discuss a distinctive mechanism for the degradation of this organic–inorganic hybrid device under long-term electrical stress. Our results demonstrated that an ionic liquid or gel gate dielectric provides highly reliable and low-voltage operation with IGZO TFTs. Furthermore, high-density carrier accumulation helps improve the TFT characteristics and reliability and it is highly relevant to the electronic phase control of oxide materials and the degradation mechanism for organic–inorganic hybrid devices.

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 SiN x and SiO x 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.

We report the fabrication of high mobility amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) irradiated by a single shot of a 248 nm KrF excimer laser. Very high mobilities (μ) of up to 43.5 cm2/V s were obtained after the low temperature excimer laser annealing (ELA) process. ELA induces high temperatures primarily in the upper layers and maintains very low temperatures of less than 50 °C in the substrate region. Scanning Transmission Electron micrographs show no laser induced damage and clear interfaces after the laser irradiation. In addition, several characterization studies were performed to determine the μ improvement mechanism. The analysis of Secondary Ion Mass Spectrometry and X-ray Photoelectron Spectroscopy suggests incorporation of H mainly from the hybrid passivation layer into the channel. Moreover, Energy-dispersive X-ray Spectroscopy results show that Au diffused into the channel after ELA. Both KrF ELA-induced H and Au diffusion contributed to the higher μ. These results demonstrate...

We investigate the influence of polymer passivation on amorphous Indium Gallium Zinc Oxide (a-IGZO) TFT reliability. We made photosensitive siloxane passivation layer on bottom-gate type a-IGZO TFTs with SiO 2 /Si substrate. For photosensitive materials, contact holes can be formed by UV photolithography technique without plasma etching process, leading to serious damage to the channel layer. The samples with and without passivation layer were tested in terms of the stability during the positive bias stress (PBS; V gs = 20 V) for 1000 sec. The stability of a-IGZO TFTs was improved by using the photo-sensitive siloxane passivation layer.

Degradation by Joule heating of the thin-film transistors (TFTs) is one of the important issues for realizing next-generation displays. We have investigated the thermal distribution on the channel region of transparent amorphous oxide semiconductor TFT in pulse operation using an infrared imaging system. We also discussed the relationship between the self-heating temperature and the degradation.

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.

SiO 2 /IGZO interface was investigated by cyclic capacitance-voltage method. High pressure water vapor annealing improved interface states. We consider that this measurement method is useful for evaluating interface characteristics.

Degradation caused by Joule heating of transparent amorphous oxide semiconductor thin-film transistors (TFTs) is an important issue for display technology. Deep understanding of the mechanism of self-heating degradation generated by driving pulse voltage will pave the way for the development of highly reliable flexible displays. In this work, by using a pseudo interval measurement method, we examined the relationship of the highest and the lowest heating temperature in pulse 1 cycle and frequency. These self-heating converged to a constant temperature under pulse voltage applied at 1 kHz. Moreover, the long-term reliability under positive-bias stress voltage at 1 kHz of low converged temperature condition was improved relative to that of the stress voltage at 10 Hz of dynamic temperature change condition. We discussed the degradation mechanism of oxide TFTs generated by pulse voltage, and clarified that the degradation was accelerated by thermionic emission which occurred at low frequency.

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.

We investigated the degradation of amorphous In2O3–Ga2O3–ZnO thin-film transistors caused by dynamic AC voltage stress. When AC stress was applied, the transfer curves exhibited an increase in subthreshold swing (S) value. AC stress produced a unique phenomenon in the degradation of the S value, which did not occur under DC voltage stress. Degradation phenomena induced by the transition from positive to negative voltage under AC gate stress suggest that a high electric field introduced by switching to the negative biasing state causes degradation due to the induced high-energy electrons at the interfaces between the electrodes (source and drain) and the channel.