Amorphous Indium Tin Oxide Research Articles

Resistive switching and battery-like characteristics in highly transparent Ta2O5/ITO thin-films

Highly transparent resistive-switching (RS) devices were fabricated by growing amorphous tantalum pentoxide (a-Ta2O5) and indium tin oxide (a-ITO) thin films on barium-borosilicate glass (7059) substrates, using electron beam evaporation. These layers exhibited the transmittance greater than ~ 85% in the full visible region and showed RS behavior and battery-like IV characteristics. The overall characteristics of RS can be tuned using the top electrode and the thickness of a-Ta2O5. Thinner films showed a conventional RS behavior, while thicker films with metal electrodes showed a battery-like characteristic, which could be explained by additional redox reactions and non-Faradaic capacitive effects. Devices having battery-like IV characteristics showed higher enhanced, retention and low-operation current.

Preparation of large-scale uniformly crystallized ITO thin films by rapid infrared annealing technique

This paper proposes three engineering application technology applications for rapid infrared annealing (RIA): scanning annealing, lamp array preheating and scanning annealing, and lamp array annealing. For the dynamic scanning annealing method, the influence of the working distance from the infrared lamp to the amorphous indium tin oxide (ITO) film and the scanning speed on the heating of the film surface were studied. For lamp array preheating and scanning annealing, the attenuation of the compressive stress on the surface of the chemically strengthened glass under the condition of low temperature and the long holding time were revealed. For lamp array annealing, the influence of this technology on the optical and electrical properties of the ITO film and the surface compressive stress of chemically strengthened glass were studied. Using the lamp array preheating and scanning annealing and lamp array annealing technology, not only a crystalline ITO film with excellent optical and electrical properties and uniformity can be prepared quickly, but also the impact of the crystallization process on chemically strengthened glass can be reduced greatly.

Zinc oxide and indium tin oxide as embedding layers for ultrathin-silver-based transparent electrodes: A comparative study

The triple-layered structure comprising an ultrathin (∼10 nm) Ag layer embedded between two dielectric layers exhibits high visible light transmittance, electrical conductivity, and flexibility, and this triple-layered structure is thus considered as a promising candidate to replace the conventional single-layered indium tin oxide (ITO) transparent conductive electrodes in optoelectronic devices. While various dielectrics have been employed for the underlayer and overlayer, ITO and zinc oxide (ZnO) are the two common choices. In this study, we investigated the structural, electrical, optical, and thermal properties of triple-layered electrodes (dielectric underlayer/Ag/dielectric overlayer) comprising Ag, ZnO, and ITO; namely, ZnO/Ag/ZnO, ZnO/Ag/ITO, ITO/Ag/ITO, and ITO/Ag/ZnO electrodes, in which all layers were sputter-deposited at 293 K. The deposition of crystalline Ag onto crystalline ZnO and amorphous ITO surfaces exhibited distinctly dissimilar Ag nucleation dynamics, resulting in significant differences in the structural and thus electrical characteristics prior to Ag-layer-closure. After the formation of continuous Ag layers, the electrical conductivities became similar, whereas the optimized ITO/Ag/ZnO structure exhibited a considerably higher visible light transmittance than the other electrodes (with an average transmittance of 92.8%). Further, we found that the ZnO/Ag interface stability was significantly higher than that of the ITO/Ag interface during an electrically driven Joule heating process.

Different Crystallization Behavior of Amorphous ITO Film by Rapid Infrared Annealing and Conventional Furnace Annealing Technology.

An amorphous indium tin oxide (ITO) film (Ar/O2 = 80:0.5) was heated to 400 °C and maintained for 1-9 min using rapid infrared annealing (RIA) technology and conventional furnace annealing (CFA) technology. The effect of holding time on the structure, optical and electrical properties, and crystallization kinetics of ITO films, and on the mechanical properties of the chemically strengthened glass substrates, were revealed. The results show that the nucleation rate of ITO films produced by RIA is higher and the grain size is smaller than for CFA. When the RIA holding time exceeds 5 min, the sheet resistance of the ITO film is basically stable (8.75 Ω/sq). The effect of holding time on the mechanical properties of chemically strengthened glass substrates annealed using RIA technology is less than that of CFA technology. The percentage of compressive-stress decline of the strengthened glass after annealing using RIA technology is only 12-15% of that using CFA technology. For improving the optical and electrical properties of the amorphous ITO thin films, and the mechanical properties of the chemically strengthened glass substrates, RIA technology is more efficient than CFA technology.

Serially connected tantalum and amorphous indium tin oxide for sensing the temperature increase in IGZO thin-film transistor backplanes

A temperature sensor embedded in an In-Ga-Zn oxide (IGZO) TFT was evaluated after fabrication to facilitate monitoring of the temperature distribution on a thin-film transistor (TFT) array. Because the proposed temperature sensor uses the same material as the TFT, no additional process or material is required. Moreover, it can be used as a light shield layer because the temperature sensor is located on a TFT. The temperature sensor used in this study was serially connected to indium tin oxide and a metal. As the temperature increased to 120 °C, the output voltage of the temperature sensor increased to 176.6 mV. The sensitivity, hysteresis, and repeatability were 0.85 mV/°C, 3.56 %, and 0.04 %, respectively. The temperature sensor was integrated into an amorphous IGZO bottom-gate TFT. The TFT exhibited a field-effect mobility of 8.2 cm2V−1·s−1 and threshold voltage of 5.2 V. As the drain current increased from 300 µA to 1.1 mA, the temperature increased from 26 to 32.9 °C, and the output voltages of the temperature sensor augmented from 66 to 76 mV. The integrated temperature sensors enable us to measure the temperature distribution in a display panel and compensate for image deterioration due to increased temperature.

High-Performance Amorphous InGaSnO Thin-Film Transistor with ZrAlOx Gate Insulator by Spray Pyrolysis

Here, we report the high-performance amorphous gallium indium tin oxide (a-IGTO) thin-film transistor (TFT) with zirconium aluminum oxide (ZAO) gate insulator by spray pyrolysis. The Ga ratio in the IGTO precursor solution varied up to 20%. The spray pyrolyzed a-IGTO with a high-k ZAO gate insulator (GI) exhibits the field-effect mobility (μFE) of 16 cm2V−1s−1, threshold voltage (VTH) of −0.45 V subthreshold swing (SS) of 133 mV/dec., and ON/OFF current ratio of ~108. The optimal a-IGTO TFT shows excellent stability under positive-bias-temperature stress (PBTS) with a small ΔVTH shift of 0.35 V. The enhancements are due to the high film quality and fewer interfacial traps at the a-IGTO/ZAO interface. Therefore, the spray pyrolyzed a-IGTO TFT can be a promising candidate for flexible TFT in the next-generation display.

Solution-processed amorphous zinc indium tin oxide thin-film transistors with high stability under AC stress

Amorphous zinc–indium–tin oxide thin-film transistors with various Zn : In : Sn ratios are investigated to improve AC stress stability by suppressing hot carrier effects in the channel layer.

Ion-gating analysis on conduction mechanisms in oxide semiconductors

• Self-gated field-effect by ion adsorption at the solid–liquid interface (ion-gating). • Resistive factors of indium tin oxide controlled depending on sputtering conditions. • A fundamental correlation between the ion-gating effect and the resistive factors. • Ion-gating analysis on the resistance-dependent behavior of electrons in the electrode. • Identification of conduction mechanisms in amorphous oxide semiconductors. The electric field-effect is one of the common methods to tune the conductivity of materials in semiconductor devices because it can control the accumulation or depletion of charge carriers. However, to efficaciously dominate the electrical properties of the semiconductor in such a way, the application of an external voltage through the gate is an inevitable condition. Here, we propose an ion-dynamics-driven (ionovoltaic) transducer focusing on a self-gated field-effect by ion adsorption at the solid–liquid interface (an ion-gating effect without applied electric field). Considering an effective resistance derived from the generated signal, we establish an equivalent circuit of the ion-gating field-effect transducer to specifically analyze the conduction behavior of traveling electrons in an amorphous indium tin oxide film. As a result, using water droplet flow, we provide a convenient method to identify inherent conduction mechanisms of amorphous oxide semiconductors. This analysis has great potential as a tool to leap forward into a new interdisciplinary approach covering interface science and solid-state physics from a peculiar concept based on the ion-gating effect.

ITO@TiO2 nanoarray: An efficient and robust nitrite reduction reaction electrocatalyst toward NH3 production under ambient conditions

Ambient electrochemical nitrite (NO2-) reduction is viewed as an effective and sustainable approach for simultaneously removing NO2- and producing ammonia (NH3). However, the complex multi-electron transfer steps involved in the NO2- reduction reaction (NO2-RR) lead to sluggish kinetics and low product selectivity toward NH3, underscoring the need for NH3 synthesis electrocatalysts with high activity and durability. Herein, we report amorphous indium–tin oxide sputtered on a TiO2 nanobelt array on a Ti plate (ITO@TiO2/TP) as a 3D NH3-producing catalyst for the NO2-. In 0.5 ​M LiClO4 with 0.1 ​M NO2-, it shows greatly boosted NO2-RR activity toward NH3 production, with excellent selectivity, achieving a large NH3 yield of 411.3 ​μmol ​h−1 ​cm−2 and a high Faradaic efficiency of 82.6%. It also shows high durability for continuous electrolysis. A Zn‐NO2- battery with ITO@TiO2/TP cathode offers an NH3 yield of 23.1 ​μmol ​h−1 ​cm−2 and a peak power density of 1.22 ​mW ​cm−2.

12.42% Monolithic 25.42 cm2 Flexible Organic Solar Cells Enabled by an Amorphous ITO-Modified Metal Grid Electrode.

Printed metal nanogrid electrode exhibits superior characteristics for use in flexible organic solar cells (OSCs). However, the high surface roughness and inhomogeneity between grid and blank region is adverse for performance improvement. In this work, a thin amorphous indium tin oxide (ITO) film (α-ITO) is introduced to fill the blank and to improve the charge transporting. The introduction of α-ITO significantly improves the comprehensive properties of metal grid electrode, which exhibits excellent bending resistance and long-term stability under double 85 condition (under 85°C and 85% relative humidity) for 200 h. Both experimental and simulation results reveal α-ITO with a sheet resistance of 20 000 Ω □-1 is sufficient to improve the charge transporting within the adjacent grids, leading to a remarkable efficiency of 16.54% for 1 cm2 flexible devices. With area increased to 4.00, 9.00, and 25.42 cm2 , the devices still display a performance of 16.22%, 14.69%, and 12.42%, respectively, showing less efficiency loss during upscaling. And the 25.42 cm2 monolithic flexible device exhibits a certificated efficiency of 12.03%. Moreover, the device shows significantly improved air stability relative to conventional high-conductive poly(3,4-ethylenedioxythiophene):polystyrene sulfonate-modified device. All these make the α-ITO-modified Ag/Cu electrode promise to achieve high-efficient and long-term stable large-area flexible OSCs.

Transparent Flexible Piezoelectric Ultrasound Transducer for Photoacoustic Imaging System

Photoacoustic imaging (PAI) has become a popular technique for biomedical diagnosis. However, current systems are overly complex or use bulky piezoelectric materials, necessitating options other than these methods for future PAI systems. In this study, a wearable transparent ultrasonic transducer was developed and applied in a PAI system with excellent performance. The acoustic sensor was fabricated with a sandwich structure consisting of 150 nm thick amorphous indium tin oxide on both sides of a <inline-formula> <tex-math notation="LaTeX">$110~\mu \text{m}$ </tex-math></inline-formula> commercial polyvinylidene fluoride film. This single-element sensor exhibited the performance of a 6.7 MHz center frequency, an 86.3&#x0025; &#x2212;3 dB fractional bandwidth, and a <inline-formula> <tex-math notation="LaTeX">$20\times20\,\,\times $ </tex-math></inline-formula> 36 mm³ volumetric imaging field. Modified imaging phantoms were made to evaluate the lateral resolution, imaging depth, ability to make a convex photoacoustic image, quality of 3D imaging, and capability to perform PAI directly in the ambient environment with a customized phantom. In summary, the study has demonstrated the sensor&#x2019;s potential for large-field PAI application in wearable health devices at a low cost.

Influences of vacuum annealing induced oxygen defects on the transfer characteristics of a-ITO thin-film transistors

Amorphous indium–tin-oxide (a-ITO) films are fabricated by pulsed laser deposition at room temperature and annealed in vacuum. Although vacuum annealing could ameliorate the carrier mobility and subthreshold swing, the threshold voltage shows a negative shift upon vacuum annealing at 450 K, and a hump emerges in the subthreshold region. The density of electronic states extracted by Grünewald method demonstrate that the hump is caused by shallow donor-like states. Furthermore, the X-ray photoelectron spectra and the photoconductivity experiment reveal that the shallow donors are ascribed to the increased oxygen defects upon thermal annealing.

Effect of Oxygen Flow Rate on Properties of Aluminum-Doped Indium-Saving Indium Tin Oxide (ITO) Thin Films Sputtered on Preheated Glass Substrates

Amorphous aluminum-doped indium tin oxide (ITO) thin films with a reduced indium oxide content of 50 mass% were manufactured by co-sputtering of ITO and Al2O3 targets in a mixed argon–oxygen atmosphere onto glass substrates preheated at 523 K. The oxygen gas flow rate and heat treatment temperature effects on the electrical, optical and structural properties of the films were studied. Thin films were characterized by means of a four-point probe, ultraviolet–visible-infrared (UV–Vis-IR) spectroscopy and X-ray diffraction. Transmittance of films and crystallization temperature increased as a result of doping of the ITO thin films by aluminum. The increase in oxygen flow rate led to an increase in transmittance and hindering of the crystallization of the aluminum-doped indium saving ITO thin films. It has been found that the film sputtered under optimal conditions showed a volume resistivity of 713 µΩ cm, mobility of 30.8 cm2/V·s, carrier concentration of 2.9 × 1020 cm−3 and transmittance of over 90% in the visible range.

Unveiling the Annealing-Dependent Mechanical Properties of Freestanding Indium Tin Oxide Thin Films.

A fundamental understanding of the mechanical behavior of the indium tin oxide (ITO) layer is very important because cracking and delamination of the ITO layers have been a critical obstacle for mechanically robust flexible electronics. In this study, the intrinsic mechanical properties of ITO thin films without a substrate were measured by utilizing a freestanding tensile testing method. Young's modulus (89 ± 1 GPa), elongation (0.34 ± 0.02%), and tensile strength (293 ± 13 MPa) of amorphous as-deposited ITO thin films were successfully measured. The sheet resistance, transparency, and thickness of the as-deposited films were 32.9 ± 0.5 Ω/sq, 92.7% (400-700 nm), and 152 ± 6 nm, respectively. First, we investigated the effects of annealing temperature on the mechanical properties of ITO thin films. For 100- and 150 °C-annealed ITO thin films, which were amorphous, Young's modulus, elongation, and tensile strength were enhanced by increasing the packing density and reducing the structural defects. For 200 °C-annealed ITO thin films, which were polycrystalline, Young's modulus was further increased because of their highly packed crystalline nature. However, there was a significant decrease in elongation and tensile strength because grain boundaries act as critical defects. Next, the annealing time was varied from 0.5 to 6 h for a better understanding of the effects of the annealing time. As a result, the maximum elongation (0.54 ± 0.03%) and tensile strength (589 ± 11 MPa) were obtained at 150 °C for 1 h. Annealing for 1 h was appropriate for sufficient defect reduction; however, excessive annealing for more than 1 h increased the degree of partial crystallization of the ITO thin films. The proposed annealing conditions and the corresponding mechanical properties provide guidelines for the optimum annealing process of ITO thin films and quantitative data for mechanical analysis to design mechanically robust flexible electronics.

Probing free carrier plasmons in doped semiconductors using spatially resolved electron energy loss spectroscopy

We report spatially resolved measurements of free carrier collective excitations in a doped semiconductor. Using $\ensuremath{\sim}10$ meV resolution electron energy loss spectroscopy (EELS) in an electron microscope with $\AA{}$ spatial resolution, we identify both surface and bulk carrier plasmons at infrared energies in a freestanding film of indium tin oxide (ITO). The interference patterns of long wavelength propagating surface carrier plasmons are revealed using spatially resolved EELS, from which we extract a dispersion relation. We further show that the energies of these plasmons vary near the surfaces and grain boundaries of the film due to band bending. Modeling based on dielectric theory agrees very well with experimental results. Finally, carrier plasmons in amorphous and crystalline ITO films are compared. These results should also be helpful for understanding the free carrier plasmons in other doped semiconductors in nanoscale volumes.

High-temperature optical properties of indium tin oxide thin-films

Indium tin oxide (ITO) is one of the most widely used transparent conductors in optoelectronic device applications. We investigated the optical properties of ITO thin films at high temperatures up to 800 °C using spectroscopic ellipsometry. As temperature increases, amorphous ITO thin films undergo a phase transition at ~ 200 °C and develop polycrystalline phases with increased optical gap energies. The optical gap energies of both polycrystalline and epitaxial ITO thin films decrease with increasing temperature due to electron–phonon interactions. Depending on the background oxygen partial pressure, however, we observed that the optical gap energies exhibit reversible changes, implying that the oxidation and reduction processes occur vigorously due to the low oxidation and reduction potential energies of the ITO thin films at high temperatures. This result suggests that the electronic structure of ITO thin films strongly depends on temperature and oxygen partial pressure while they remain optically transparent, i.e., optical gap energies > 3.6 eV.

Highly transparent conductors for optical and microwave access to spin-based quantum systems

Spin-based quantum systems are among the best sensors in terms of sensitivity and spatial resolution for a variety of physical properties. A key factor to broaden the range of applications is the control over the microwave field used to manipulate the quantum system. We present the implementation of a transparent microwave conductor, suitable for optical read-out of a spin-based quantum sensor. For this, the interaction of an indium tin oxide (ITO) strip line on diamond with nitrogen vacancy centres was investigated. The amorphous ITO can be fabricated at room temperature, has a transmittance larger than 80% in the visible spectrum and a low resistivity. We show that these strip lines are completely scalable which enables highly homogeneous microwave fields from the nanometre up to the millimetre scale. ITO structures can therefore serve as excellent transparent microwave conductors, widening the current use of spin-based quantum sensors.

Preparation of Low-Resistance and Residue-free ITO Films for Large-scale 3D Displays.

The large-sized naked-eye three-dimensional (3D) display is a critical device in the real-time topographic survey for deep-sea scientific research. As a core component, the low-impedance transparent conductive indium tin oxide (ITO) thin-film electrode lacks a reliable industrial preparation method. In the 3D display, the grating element with a low-resistance ITO film electrode should have a good binocular parallax to drive the display favorably. However, an increase in the ITO film temperature during deposition may induce its crystallization, and its etching residue may cause a short circuit between the ITO electrodes and abnormal display operation. In this work, we propose a simple and straightforward technique to produce amorphous thin ITO films by controlling the water vapor flow rate during the deposition process. The obtained ITO amorphous thick film (300 nm) can be etched without leaving residues on the display surface, ensuring vivid display performance of the 3D display. A field test employing the 3D display, consisting of a 3D parallax barrier and a two-dimensional (2D) display, does not exhibit a short-circuit phenomenon caused by residues encountered in previous devices. This work makes the 3D display applicable for the real-time topographic survey on the basis of both satisfying the nonetching residue and the decrease of the resistance value.

Ultra-flat ITO films on mica for high temperature transparent flexible electrodes

Indium tin oxide (ITO) films were deposited on transparent and flexible mica substrates by RF magnetron sputtering at room temperature. The ITO films exhibit atomically flat morphology on the cleaved natural mica surface. Excellent thermal stability of mica allows heat treatment at high temperature up to 500 oC. The electronic and optical characteristics of the ITO films are improved by annealing process, which can be explained by the preferred (2 2 2)-oriented crystallization at temperatures higher than 200 oC. The resistivity of as-deposited amorphous ITO film is ~2.1 × 10−3 Ωcm and remarkably decrease to ~5.0 × 10−4 Ωcm for the annealed samples. Accompanying the rapid increase in the conductivity, the transmittance also increases to more than 90% for the crystallized ITO films. Furthermore, the mechanical tests indicate excellent flexibility and durability of the ITO films on mica. These results demonstrate that the ITO films on mica can endure high temperature process for the applications in flexible electronics.

Ultrathin channels make transistors go faster.

Reducing the thickness of an amorphous conductive indium tin oxide layer down to a few nanometres has enabled the realization of 40-nm-long channel transistors with remarkable operating characteristics.