Crystalline Indium Tin Oxide Research Articles

Junctionless Structure Indium-Tin Oxide Thin-Film Transistors Enabling Enhanced Mechanical and Contact Stability.

In recent years, considerable attention has focused on high-performance and flexible crystalline metal oxide thin-film transistors (TFTs). However, achieving both high performance and flexibility in semiconductor devices is challenging due to the inherently conductive and brittle nature of crystalline metal oxide. In this study, we propose a facile way to overcome this limitation by employing a junctionless (JL) TFT structure via oxygen plasma treatment of the crystalline indium-tin oxide (ITO) films. The oxygen plasma treatment significantly reduced oxygen vacancies in the ITO films, contributing to the significant reduction in the carrier concentration from 4.67 × 1020 to 1.39 × 1016. Importantly, this reduction was achieved without inducing any noticeable structural changes in the ITO, enabling the successful realization of ITO JL TFTs with an adjustable threshold voltage. Furthermore, the ITO JL TFTs demonstrate good stability and reliability under various bias stress conditions, aging in the air atmosphere, and high-temperature processes. In addition, the ITO JL TFTs exhibit low light sensitivity due to the wide bandgap of ITO and further suppression of Vo defects, making them suitable for applications requiring stable performance under light exposure. To compare and analyze the flexibility of the JL structure and conventional structure with additional source/drain (S/D) junction in ITO TFTs with nonencapsulation, we utilized mechanical simulations and transmission line method (TLM). By employing the JL structure in ITO TFT through carefully optimized oxygen plasma treatment, we successfully mitigated stress concentration at the S/D-channel interface. This resulted in a JL ITO TFT that exhibited a change in contact resistance of less than 20% even after 20,000 bending cycles. Consequently, a stable and flexible ITO TFT with field-effect mobility (μFE) of 12.74 cm2/(V s) was realized, outperforming conventionally structured ITO TFTs with additional S/D junction, where the contact resistance nearly tripled.

In-situ construction of plasma-pretreated CNT networks endow the LPDS dual-layer coating with advanced thermal management and anti-static properties

Carbon nanotubes (CNTs) for temperature regulation have been proven to be promising for passive radiative heat dissipation. However, it remains a considerable challenge to assemble a CNTs layer in situ while simultaneously achieving horizontal electrical conductivity, vertical electrical insulation, and radiative heat dissipation. Herein, plasma pretreatment was employed to functionalize CNTs in an aqueous solution, thus improving their dispersion capability. Subsequently, a liquid-plasma-assisted particle deposition and sintering (LPDS) technology was proposed to prepare a dual-layer coating with an Al2O3-P2O5-SiO2-In2O3 glass system embedded with crystalline indium tin oxide (ITO) as the porous bottom layer and ITO-CNTs as the top layer on the aluminum alloy surface. The results show that plasma pretreatment significantly increases the deposition amount of ITO nanoparticles and functionalized CNTs on the coating surface, resulting in the transition from a single-layer composite coating to a dual-layer coating. The surface micro-/nano hierarchical structure favors strong absorptance/emittance, exhibiting a high infrared emittance of 0.94 (3-20 μm) and high solar absorptance of 0.92 (0.2-2.5 μm). Meanwhile, the surface balance temperature of the dual-layer coating is about 392 K, which is 146 K lower than that of aluminum alloy. Furthermore, the top conductive ITO-CNTs layer contributes to the low surface resistivity of 3.46×102 Ω, while the glass phase of the bottom layer ensures vertical electrical insulation with a volume resistance of 4.20×107 Ω. The process provides a new path for preparing thermal control coatings with anti-static function.

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.

A controllable fabrication of flat absorber dual-layer coating with electric shielding on 6061 aluminum alloy by PEO with nanoparticles additive

In spacecraft, thermal control coatings with anti-static functionality are vital for electronic packages to ensure proper operation of devices and instruments while preventing the reduction of component lifetime due to extreme temperatures or electrostatic discharge. However, simultaneously integrating thermal control and static charge dissipation into one coating remains a huge challenge. Herein, a dual-layer black coating composed of an Al2O3-In2O3-P2O5-SiO2 glass bottom layer embedded with crystalline indium tin oxide (ITO) and a top layer with ITO and carbon nanotubes (CNTs) as sealed conductive and radiative components grows in situ on the 6061 aluminum alloy surface using a modified PEO method with nanoparticles additive under special parameters, experiencing one-step liquid-plasma-assisted particle deposition and sintering (LPDS) process. During the LPDS process, the addition of CNTs to the electrolyte promotes the deposition and sintering of ITO nanoparticles on the bottom layer, resulting in the transition from a single-layer coating to a dual-layer coating. CNTs with high absorption/emissivity assisted further by the infrared-trapping effect of the micro/nanostructure lead to flat absorber dual-layer coating. The black coating offers both high solar absorptance (~0.93) in the 0.2–2.5 μm waveband and infrared emissivity (~0.94) in the 3–20 μm waveband. Notably, CNTs with high aspect ratio connect the ITO nanoparticles to form a complete conductive channel on the coating surface, thus eliminating in-plane charges. At only 1.27 × 102 Ω, the surface resistivity of the dual-layer coating is five orders of magnitude lower than that of the single-layer Al2O3 coating (1.15 × 107 Ω). Such an all-in-one design provides a feasible and sustainable strategy for anti-static black products in space applications.

Versatile Solution‐Processed Organic–Inorganic Hybrid Superlattices for Ultraflexible and Transparent High‐Performance Optoelectronic Devices

AbstractCrystalline or amorphous metal oxides are widely used in various optoelectronic devices as key components, such as transparent conductive electrodes, dielectrics or semiconducting active layers for thin‐film transistor (TFT) backplanes in large‐area displays, photovoltaics, and light‐emitting diodes. Although crystalline inorganic materials demonstrate outstanding optoelectronic performance, owing to their wide bandgaps, large conductivities, and high carrier mobilities, their inherent brittleness makes them vulnerable to mechanical stress, thereby limiting the use of metal‐oxide films in emerging flexible electronic applications. In this study, stress‐diffusive organic–inorganic hybrid superlattice nanostructures are developed to overcome the mechanical limitation of crystalline oxides and to provide high mechanical stability to metal‐oxide semiconductors. In particular, hybrid transparent superlattice electrodes based on crystalline indium–tin oxide exhibit high electrical conductivities of up to 555 S cm–1 (resistance variation < 3%) and effectively reduce the mechanical stress on the inorganic layer (up to 10 000 bending cycles with a radius of 1 mm). Furthermore, to ensure the viability of the hybrid superlattice flexible electronics, all solution‐processed superlattice crystalline indium–gallium‐oxide TFTs are implemented on a thin (≈5 µm) polyimide substrate, providing highly robust and excellent electrical performance (average mobility of 7.6 cm2 V–1 s–1).

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.

Effects of Zn Ratio Tuning on the Structural and Transport Properties of Amorphous Indium Zinc Tin Oxide Thin Films

In this study, various indium zinc tin oxide (IZTO) films were fabricated using co-sputtering to explore amorphous transparent conducting oxides as alternatives to crystalline indium tin oxide (ITO). Various Zn ratios were tuned to study their effects on the structural evolution of IZTO. Amorphous IZTO (aIZTO) films were obtained when the Zn concentration was higher than approximately 17 at.%. X-ray diffraction and transmission electron microscopy analyses indicated that amorphous structures were formed due to the high crystallization temperatures of IZTO and nanocrystalline In2Zn5O8, which also caused aIZTO to exhibit small band gaps. On average, 87% transmittance was achieved in the visible light range. The aIZTO films had substantially higher transmittance in the infrared region than the ITO films did. Samples with Zn ratios between approximately 17 at.% and 27 at.% exhibited resistivity (approximately 3 × 10−4 Ω-cm), mobility (7 cm2 V−1 s−1), and carrier concentrations (4 × 1021 cm−3) comparable to those of crystalline ITO. Thus, the aIZTO films are promising alternative TCO materials. The mechanisms of competition between the crystallinity, oxygen deficiency, high-mobility In2Zn5O8, and electron and hole generation rates were applied to shed light on the excellent electrical and transport properties of aIZTO films.

Role of plasma parameters on the characteristics properties of flexible transparent ITO films deposited by 3D facing and planar facing magnetron sources

A rectangular closed and hollow three-dimensionally confined large area magnetron source (3-DCLAMS) and a conventional moderate area facing target magnetron source (FTMS) have been used to study the plasma characteristics using different diagnostics at different working pressures. Flexible indium tin oxide (ITO) films deposited at similar operating conditions using these sources were characterized by numerous standard analyses to study their film properties. The 3-DCLAMS with high discharge current at a low-discharge voltage is capable of generating high plasma density, which assists a high ion flux and energy density on the substrate that is necessary for the high growth rate deposition of highly conductive crystalline ITO films with smooth surface morphology. Utilizing suitable plasma characteristics, highly conductive and transparent ITO films of 30 nm with the minimum resistivity ρ ∼ 4.1 × 10−4 Ω cm and ∼9.3 × 10−4 Ω cm and average transmittance T ∼ 84% and 82%, respectively, were deposited in the 3-DCLAMS and the FTMS system. The presented result shows that the 3-DCLAMS system could be useful for making high-quality, flexible ITO films at a very high deposition rate of ∼250 nm/min.

Matrix-material dependence on the elongation of embedded gold nanoparticles induced by 4 MeV C60 and 200 MeV Xe ion irradiation

We report the elongation of embedded Au nanoparticles (NPs) in three different matrices, i.e. amorphous carbon (a-C), crystalline indium tin oxide (InxSn1-xOz; ITO) and crystalline calcium fluoride (CaF2), under irradiations of 4 MeV C60+ cluster ions and 200 MeV Xe14+ ions. Under 4 MeV C60 cluster irradiation, strong sputtering is induced in CaF2 layer so that the whole the layer was completely lost at a fluence of 5 × 1013 ions cm−2. Au NPs were partly observed in the SiO2, probably due to the recoil implantation. Amorphous carbon (a-C) layer exhibits low sputtering loss even under 4 MeV C60 irradiation. However, the elongation in a-C layer was low. While the ITO layer showed a certain decrease in thickness under 4 MeV C60 irradiation, large elongation of Au NPs was observed under both 4 MeV C60 and 200 MeV Xe irradiation. The ITO layer preserved the crystallinity even after large elongation was induced. This is the first report of the elongation of metal NPs in a crystalline matrix.

Optical and electrical properties of crystalline indium tin oxide thin film deposited by vacuum evaporation technique

Indium tin oxide (ITO) thin film was deposited on glass substrate by means of vacuum evaporation technique and annealed at 200 °C, 300 °C and 400 °C in air for 1 h. The characterization and properties of the deposited film samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-VIS-NIR spectroscopy techniques. From the XRD patterns, it was found that the deposited thin film was of crystalline at an annealing temperature of 400 °C. The crystalline phase was indexed as cubic structure with lattice constant and crystallite size of 0.511 nm and 40 nm, respectively. The SEM images showed that the films exhibited uniform surface morphology with well-defined spherical grains. The optical transmittance of ITO thin film annealed at 400 °C was improved from 44% to 84% in the wavelength range from 250 nm to 2 100 nm and an optical band gap was measured as 3.86 eV. Hall effect measurement was used to measure the resistivity and conductivity of the prepared film.

Microfluidic electrochemical cell for in situ structural characterization of amorphous thin-film catalysts using high-energy X-ray scattering.

Porous, high-surface-area electrode architectures are described that allow structural characterization of interfacial amorphous thin films with high spatial resolution under device-relevant functional electrochemical conditions using high-energy X-ray (>50 keV) scattering and pair distribution function (PDF) analysis. Porous electrodes were fabricated from glass-capillary array membranes coated with conformal transparent conductive oxide layers, consisting of either a 40 nm-50 nm crystalline indium tin oxide or a 100 nm-150 nm-thick amorphous indium zinc oxide deposited by atomic layer deposition. These porous electrodes solve the problem of insufficient interaction volumes for catalyst thin films in two-dimensional working electrode designs and provide sufficiently low scattering backgrounds to enable high-resolution signal collection from interfacial thin-film catalysts. For example, PDF measurements were readily obtained with 0.2 Å spatial resolution for amorphous cobalt oxide films with thicknesses down to 60 nm when deposited on a porous electrode with 40 µm-diameter pores. This level of resolution resolves the cobaltate domain size and structure, the presence of defect sites assigned to the domain edges, and the changes in fine structure upon redox state change that are relevant to quantitative structure-function modeling. The results suggest the opportunity to leverage the porous, electrode architectures for PDF analysis of nanometre-scale surface-supported molecular catalysts. In addition, a compact 3D-printed electrochemical cell in a three-electrode configuration is described which is designed to allow for simultaneous X-ray transmission and electrolyte flow through the porous working electrode.

Fabrication of Nanopillar Crystalline ITO Thin Films with High Transmittance and IR Reflectance by RF Magnetron Sputtering.

Nanopillar crystalline indium tin oxide (ITO) thin films were deposited on soda-lime glass substrates by radio frequency (RF) magnetron sputtering under the power levels of 100 W, 150 W, 200 W and 250 W. The preparation process of thin films is divided into two steps, firstly, sputtering a very thin and granular crystalline film at the bottom, and then sputtering a nanopillar crystalline film above the bottom film. The structure, morphology, optical and electrical properties of the nanopillar crystalline ITO thin films were investigated. From X-ray diffraction (XRD) analysis, the nanopillar crystalline thin films shows (400) preferred orientation. Due to the effect of the bottom granular grains, the crystallinity of the nanopillar crystals on the upper layer was greatly improved. The nanopillar crystalline ITO thin films exhibited excellent electrical properties, enhanced visible light transmittance and a highly infrared reflectivity in the mid-infrared region. It is noted that the thin film deposited at 200 W showed the best combination of optical and electrical performance, with resistivity of 1.44 × 10−4 Ω cm, average transmittance of 88.49% (with a film thickness of 1031 nm) and IR reflectivity reaching 89.18%.

Roll-to-Roll fabrication of ITO thin film for flexible optoelectronics applications: The role of post-annealing

We have developed and examined new and cost effective methods for fabrication indium tin oxide (ITO) film on flexible substrate. The ITO film is deposited to polyethylene terephthalate film using roll-to-roll (RTR) sputtering advanced technology. The film's properties are evaluated before and after heat treatment. Effect of post annealing time on the electrical, optical, structural and surface properties of RTR sputtered ITO films is estimated. In addition, mechanical flexibility of as-sputtered amorphous ITO and annealed crystalline ITO films are compared. It is estimated that post-annealing at 150 °C reduces sheet resistance and increase the optical transmittance of the ITO films. The best results are observed when annealing time is 60 min. In this case the sheet resistance of ITO is measured to be 125 Ω/sq. and optical transmittance is 87.3% at wavelength range from 380 nm to 780 nm. It is demonstrated successful operation of touch screen panels fabricated on annealed ITO film. It is estimated that post-annealing significantly improves ITO performance as compare of that as-deposited film. Based on Hall measurement and transmittance electron microscopy examinations, possible mechanism to explain the effect of post-annealing time on RTR sputtered ITO films is manifested.

Thermoelectric properties and thermal tolerance of indium tin oxide nanowires

Highly crystalline indium tin oxide (ITO) nanowires were grown via a vapor–liquid–solid method, with thermal tolerance up to ∼1300 °C. We report the electric and thermoelectric properties of the ITO nanowires before and after heat treatments and draw conclusions about their applicability as thermoelectric building blocks in nanodevices that can operate in high temperature conditions. The Seebeck coefficient and the thermal and electrical conductivities were measured in each individual nanowire by means of specialized micro-bridge thermometry devices. Measured data was analyzed and explained in terms of changes in charge carrier density, impurities and vacancies due to the thermal treatments.

In-Situ Growth and Characterization of Indium Tin Oxide Nanocrystal Rods

Indium tin oxide (ITO) nanocrystal rods were synthesized in-situ by a vapor-liquid-solid (VLS) method and electron beam evaporation technique. When the electron-beam gun bombarded indium oxide (In2O3) and tin oxide (SnO2) mixed sources, indium and tin droplets appeared and acted as catalysts. The nanocrystal rods were in-situ grown on the basis of the metal catalyst point. The nanorods have a single crystal structure. Its structure was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The surface morphology was analyzed by scanning electron microscopy (SEM). During the evaporation, a chemical process was happened and an In2O3 and SnO2 solid solution was formed. The percentage of doped tin oxide was calculated by Vegard’s law to be 3.18%, which was in agreement with the mixture ratio of the experimental data. The single crystal rod had good semiconductor switch property and its threshold voltage of single rod was approximately 2.5 V which can be used as a micro switch device. The transmission rate of crystalline nanorods ITO film was over 90% in visible band and it was up to 95% in the blue green band as a result of the oxygen vacancy recombination luminescence.

Eco-friendly method of fabricating indium-tin-oxide thin films using pure aqueous sol-gel

An indium-tin-oxide (ITO) thin film with approximately 50 nm thickness was successfully synthesized on glass substrates by using a fully aqueous sol-gel process. The sol was prepared from indium nitrate hydrate and tin fluoride as a precursor. Thermogravimetric analysis confirmed that the sol converted into crystalline ITO at 286 °C. The optical band gap and transmittance of the thin film were observed to increase with annealing temperature and plasma treatment time. X-ray photoelectron spectroscopy and transmittance studies established that the number of oxygen vacancies in the thin film drastically increased with increasing temperature and plasma treatment. The annealing temperature and argon plasma treatment time appear to be key factors in reducing resistivity and increasing the transmittance of the thin film. A considerable decrease in the resistivity of the ITO thin film was observed after Ar plasma treatment. This eco-friendly sol-gel ITO thin film may find potential applications in n-type ohmic electrodes for ink-jet printable electronics.

Effect of different thermo-treatment at relatively low temperatures on the properties of indium‑tin-oxide thin films

Pulsed DC magnetron sputtering was used to deposit indium‑tin-oxide (ITO) thin films on glass substrates for application in photovoltaic devices as the final window layer. The evolution of crystal phase, morphology, resistivity and transmittance of the ITO films under different thermal annealing procedure (in-situ annealing versus post-annealing) at relatively low temperatures (up to 300°C) were studied. Fully crystalline ITO films with low sheet resistance of 24Ω/□ and high average transmittance (exclude glass substrate) of 90.10% with a Haacke's figure of merit 1.47×10−2Ω−1 were obtained by in-situ annealing at 200°C. In comparison, the minimum temperature observed to fully crystalize the ITO thin films with competitive crystallinity, electrical and optical properties by post-annealing was 250°C. The corresponding post-annealed 300nm thick films showed sheet resistance of 49Ω/□ and average transmittance (exclude glass substrate) as high as 91.93% with a Haacke's figure of merit 0.882×10−2Ω−1. The surface morphology of the as-deposited ITO films remained homogeneous after post-annealing whereas large particles (up to 100nm) were observed on the surface of the films deposited by in-situ annealing. The results indicated that different thermal treatment procedures at lower temperatures produce significant effect on the electrical, optical and other physical properties of the ITO thin films which are critical for the window layer in photovoltaics.

Flexible Indium\u2013Tin Oxide Crystal on Plastic Substrates Supported by Graphene Monolayer

Flexible and crystallized indium–tin oxide (ITO) thin films were successfully obtained on plastic polyethylene terephthalate (PET) films with monolayered graphene as a platform. The highly crystalline ITO (c-ITO) was first fabricated on a rigid substrate of graphene on copper foil and it was subsequently transferred onto a PET substrate by a well-established technique. Despite the plasma damage during ITO deposition, the graphene layer effectively acted as a Cu-diffusion barrier. The c-ITO/graphene/PET electrode with the 60-nm-thick ITO exhibited a reasonable sheet resistance of ~45 Ω sq−1 and a transmittance of ~92% at a wavelength of 550 nm. The c-ITO on the monolayered graphene support showed significant enhancement in flexibility compared with the ITO/PET film without graphene because the atomically controlled monolayered graphene acted as a mechanically robust support. The prepared flexible transparent c-ITO/graphene/PET electrode was applied as the anode in a bulk heterojunction polymer solar cell (PSC) to evaluate its performance, which was comparable with that of the commonly used c-ITO/glass electrode. These results represent important progress in the fabrication of flexible transparent electrodes for future optoelectronics applications.

Direct Patterning of Robust One-Dimensional, Two-Dimensional, and Three-Dimensional Crystalline Metal Oxide Nanostructures Using Imprint Lithography and Nanoparticle Dispersion Inks

Dimensionally stable one-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) high aspect ratio crystalline metal oxide nanostructures are fabricated using soft nanoimprint lithography with inks comprised of nanoparticle (NP) dispersions in solvent or in sol–gel precursors for the metal oxide. Crystalline TiO2 and indium tin oxide (ITO) NP dispersions in solvent are imprinted using a solvent permeable patterned poly(dimethylsiloxane) (PDMS) stamp to yield robust crystalline nanostructures that are dimensionally stable to calcination (less than 8% linear shrinkage in imprinted feature heights upon heat treatment at 500 °C). Inks comprised of 80% crystalline NPs dispersed in 20% sol–gel binder are patterned using thermal- or UV-assisted imprinting with a PDMS stamp. The composition and physical properties of the dimensionally stable imprinted metal oxides (TiO2 and ITO) can be altered by varying the composition of the ink. Rapid printing of high aspect ratio nanostructures and sub-100 nm fe...

Effect of Temperature on Nucleation of Nanocrystalline Indium Tin Oxide Synthesized by Electron-Beam Evaporation

Indium tin oxide (ITO) has been widely applied as a transparent conductive layer and optical window in light-emitting diodes, solar cells, and touch screens. In this paper, crystalline nano-sized ITO dendrites are obtained using an electron-beam evaporation technique. The surface morphology of the obtained ITO was studied for substrate temperatures of 25°C, 130°C, 180°C, and 300°C. Nano-sized crystalline dendrites were synthesized only at a substrate temperature of 300°C. The dendrites had a cubic structure, confirmed by the results of x-ray diffraction and transmission electron microscopy. The growth mechanism of the nano-crystalline dendrites could be explained by a vapor–liquid–solid (VLS) growth model. The catalysts of the VLS process were indium and tin droplets, confirmed by varying the substrate temperature, which further influenced the nucleation of the ITO dendrites.