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We report the enhancement in the electrical performance of solution-processed amorphous InZnO ( $a$ -IZO) thin-film transistors (TFTs) through incorporation of low-temperature photosensitive polysilsesquioxane (P-PSQ) passivation. P-PSQ passivated TFTs recorded smaller ${V}_{th}$ shift of 1.5 V after positive bias stress test despite annealing at 180°C. Analysis of secondary ion mass spectrometry and x-ray photoelectron spectroscopy showed that higher concentration of hydrogen reduced the amount of oxygen vacancies in the passivated IZO channel which promotes better stability against bias stress. Also, the time evolution of the ${V}_{th}$ was defined in which the activation energy for each sample was extracted. Passivated TFT also showed minimal change upon exposure to humidity test. Overall, low-temperature P-PSQ passivation is an effective barrier against atmospheric effects for solution-processed oxide TFTs.

The p-type conducting hydrogen-terminated diamond obtained from hydrogen plasma has several applications in the field of power semiconductor devices. Therefore, clarifying the effects and role of hydrogen plasma on diamond surfaces is a critical aspect in the field of hydrogen-terminated diamond devices. In this study, we focused on diamond surface etching by hydrogen plasma and revealed the dependence of the diamond crystal orientation using scanning probe microscopy and electron backscatter diffraction. Crystal grains with a low etching rate were distributed around the {100} and {111} planes, and those with a high etching rate were distributed on the {110} plane. Furthermore, we found that the etching rate increased as the intermediate orientation grains tilted toward the {110} plane. Because the surface carbon atoms that compose the {110} plane have two of their three back bonds on the surface exposed to hydrogen plasma, we expected that the {110} orientation would have a high etching rate. Even for grains with intermediate orientations, the etching tendency corresponded to the location of the back bonds. Our research provides important systematic data on the crystal orientation in diamond electronics.

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.

The reliability of oxide semiconductor TFT and the method to lower the process temperature have become serious problems. In order to solve these problems we have developed inductively coupled plasma sputtering equipment that can control the Radio Frequency (RF) power to generate Inductively Coupled Plasma (ICP) and the voltage applied to the sputtering target independently. Using this equipment, we can deposit high-density oxide semiconductor films at room temperature and fabricate highly reliable TFTs with them.

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.

Amorphous indium gallium zinc oxide thin-film transistors have attracted growing interest due to its low energy consumption, possibility of low temperature fabrication and transparency. However, it still has technological problems on reliability and hump due to hydrogen related materials. To solve these problems, we made siloxane passivation layer with less OH bond using spin coating technique and carried out the bias stress testing. TFTs passivated by less OH siloxane show excellent reliability compared with high OH bond condition which showed large hump effect on each tests of positive bias stress and negative bias stress. We achieved the stable device using an organic-inorganic hybrid material by controlling OH bond, and we found that the amount of OH in the passivation layer is a key issue in oxide TFTs reliability.

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.

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.

This report shows that an amorphous a-InGaZnO (IGZO) thin film transistor (TFT) can control the threshold voltage ( $V_{th}$ ) without thermal annealing process when depositing a-IGZO using an inductively coupled plasma (ICP) sputtering system. A two layer a-IGZO TFT with controlled oxygen concentrations was fabricated using the ICP sputtering system developed for high density thin film deposition. As a result of evaluation of TFT characteristics, a-IGZO TFTs with changed $V_{th}$ could be fabricated without a thermal annealing process.

The emphasis on ubiquitous technology means that future technological applications will depend heavily on transparent conducting materials. To facilitate truly ubiquitous applications, transparent conductors should be fabricated at low temperatures (

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.

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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.

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.

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.

Transparent amorphous oxide semiconductors (TAOS) represented by IGZO have excellent characteristics such as high mobility, and a low off current compared with amorphous Si (a-Si) semiconductor. Furthermore, TAOS can be deposit by standard sputtering systems. Large area fabrication at a lower cost than low temperature polysilicon semiconductor (LTPS) is also possible. Therefore, there is a possibility to manufacture a display with high definition / low power consumption at low cost. However, many studies have shown the insufficient electrical reliability of IGZO TFTs. Although application to flexible displays is expected, in the conventional fabrication of IGZO TFTs, post annealing processes at a high temperature of 300°C is necessary. Therefore, low temperature formation of IGZO TFT is required. The inductively coupled plasma (ICP) sputtering system under development is characterized by its capacity to deposit high density films and high target usage efficiency. Figure 1 shows the schematic of the ICP sputtering system. In this system, the antenna is installed in the chamber, and a high-frequency generator is connected to the antenna. ICP is generated in the chamber by applying high-frequency to the antennas. In this device, since the magnetic field is not arranged on the target, ICP diffuses uniformly into the chamber. In order to perform sputtering, a negative bias voltage is applied to the target, ions are pulled from the ICP, and the target material is deposited on the substrate. The target material was uniformly consumed, and usage efficiency showed a very high value of 85%. In addition, since antennas and targets are connected to independent power supplies, independent control is possible. By increasing the high-frequency power applied to the antennas and controlling the plasma density, deposition is possible without lowering deposition rate even at low target voltage. We considered that independent control of RF power and target voltage is important because both may be related to film density. The density of the IGZO films deposited by changing the RF power and the target voltage was obtained using X-ray reflectivity. The results are shown in figures 2 (a) and (b). The relationship between RF power and film density could not be confirmed. When the target voltage was increased, the film density decreased. Therefore, performing deposition at a lower target voltage yielded a high-density IGZO film. Under all conditions, the IGZO films exhibited a film density of more than 6.0 g/cm3. In this study, the bottom-gate top-contact TFTs were fabricated by low-temperature process using high-density two-layer structure IGZO film deposited by ICP sputtering system, and the transfer characteristics and reliability were examined. Bottom-gate top-contact TFTs structure is shown in figure 3. The two-layer structure IGZO (In:Ga:Zn = 1:1:1) films were deposited by ICP sputtering system with different O2/Ar gas ratio condition at room temperature. The TFTs were subjected to post annealing at 150°C or 200°C or 250°C for 2 h under the O2/N2 mixed gas atmosphere. The passivation of the photosensitive polysilsesquioxane was coated using a straightforward solution process for samples annealed at 250°C, and baked at 250°C. The TFTs were subjected to a positive gate bias stress test (PBS) by applying a gate voltage (V gs) of 20 V, for a total stress time of 10000 s. Figure 4 show transfer characteristics of each post annealing temperature. When no annealing is performed, the TFT shows switching behavior but the threshold voltage (V th) became negative. When post annealing was carried out, V th became positive. Transfer characteristics at annealing temperature of 150°C to 250°C exhibited similar values. The electric field effect mobility of V ds = 0.5 V obtained from the transfer characteristic at post annealing temperature of 150°C was 7.9 to 8.8 cm2/Vs. The results of PBS are shown in figure 5. Threshold voltage shift (ΔV th) was used as an index of reliability. ΔV th of post annealing temperature of 150°C, 200°C and 250°C were 0.73 V, 0.75 V, 0.66 V, respectively. A sample with post annealing temperature at 250°C coated with polysilsesquioxane passivation has a ΔV th = 0.09 V. The reason why TFTs showing comparatively high-mobility can be fabricated even through a low-temperature process is considered to be the deposition of high-density films with low vacancy after deposition by the ICP sputtering system. In addition, it was found that the TFT with the annealing temperature of 150°C has the same reliability as the TFT with the annealing temperature of 250°C. We are set to demonstrate TFTs showing high-reliability at low-temperature process by using passivation that can be coated even at low temperatures. Figure 1

Transparent amorphous oxide semiconducting materials such as amorphous InGaZnO used in thin film transistors (TFTs) are typically annealed at temperatures higher than 250 °C to remove any defects present and improve the electrical characteristics of the device. Previous research has shown that low cost and low temperature methods improve the electrical characteristics of the TFT. With the aid of surface and bulk characterization techniques in comparison to the device characteristics, this work aims to elucidate further on the improvement mechanisms of wet and dry annealing ambients that affect the electrical characteristics of the device. Secondary Ion Mass Spectrometry results show that despite outward diffusion of –H and –OH species, humid annealing ambients counteract outward diffusion of these species, leading to defect sites which can be passivated by the wet ambient. X-ray Photoelectron Spectroscopy results show that for devices annealed for only 30 min in a wet annealing environment, the concentration of metal-oxide bonds increased by as much as 21.8% and defects such as oxygen vacancies were reduced by as much as 18.2% compared to an unannealed device. Our work shows that due to the oxidizing power of water vapor, defects are reduced, and overall electrical characteristics are improved as evidenced with the 150 °C wet O2, 30 min annealed sample which exhibited the highest mobility of 5.00 cm2/V s, compared to 2.36 cm2/V s for a sample that was annealed at 150 °C in a dry ambient atmospheric environment for 2 h.

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...

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.

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 report the fabrication of a photosensitive hybrid passivation material on amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) that greatly enhance its stability and improve its electrical characteristics. The hybrid passivation based on polysilsesquioxane is transparent and fabricated using a simple solution process. Because the passivation is photosensitive, dry etching was never performed during TFT fabrication. TFTs passivated with this material had a small threshold voltage shift of 0.5 V during positive bias stress, 0.5 V during negative bias stress, and −2.5 V during negative bias illumination stress. Furthermore, TFTs passivated by this layer were stable after being subjected to high relative humidity stress — confirming the superb barrier ability of the passivation. Analysis of secondary ion mass spectrometry showed that a large amount of hydrogen, carbon, and fluorine can be found in the channel region. We show that both hydrogen and fluorine reduced oxygen vacancies and that fluorine stab...