High-quality Indium Tin Oxide Films Research Articles

Annealing-free fabrication of high-quality indium tin oxide films for free-carrier-based hybrid metal–semiconductor nanophotonics

Recent discoveries have revealed that indium tin oxide (ITO), due to the presence of an epsilon-near-zero (ENZ) point and suitable carrier concentration and mobility, can be used to modulate the refractive index, confine fields in the nanoscale, enhance nonlinear effects, achieve ultrafast light switching or to construct so-called time-varying media. While this potential positions ITO as a key material for future nanophotonic devices, producing ITO films with precisely engineered properties remains a significant challenge. Especially when the device’s complex geometry or incorporated materials require the fabrication process to be conducted at substrate temperatures below 100 °C and without any post-annealing treatment. Here we present a comprehensive study on the low-temperature deposition of 70 nm thick ITO films using an e-beam PVD system. The nanolayers evaporated under different conditions were characterized by SEM and AFM microscopy, Hall effect measurement system as well as spectroscopic ellipsometry. We discuss the factors influencing the optical, electrical, and morphological properties of ITO films. We show that smooth nanolayers of similar quality to annealed samples can be obtained at 80 °C by controlling the oxygen plasma parameters, and the ENZ wavelength can be tuned throughout the NIR spectral range. Finally, we show that using the proposed methodology, we fabricated ITO films with resistivity as low as 5.2 × 10–4 Ω cm, smooth surface with RMS < 1 nm, high carrier concentration reaching 1.2 × 1021 cm−3 and high transmittance (85%) in the Vis/NIR spectrum.

Influence of ITO Target on Structural, Optical, and Electrical Properties of Thin Films Deposited by Magnetron Sputtering

Indium tin oxide (ITO) targets possess good performances, thereby used to produce high-quality ITO films in transparent electrodes of various optoelectronic devices. The performance of the target greatly affects the performances of prepared ITO films. However, effect of the overall performance of ITO targets on ITO films performance is still not fully understood. ITO films were prepared with four targets by magnetron sputtering in the similar condition in this study. Effects of crystal structure, resistivity, and oxygen content of the targets on photoelectric performances of ITO films were all evaluated. Results showed the important effect of target properties on obtained film characteristics. ITO films prepared by low resistivity targets are more evenly distributed on the substrate surface. Meanwhile, oxygen content of obtained ITO films decreased as oxygen content of ITO targets used in sputtering process increased. This also significantly improved the photoelectric performances. ITO thin films deposited using targets with low resistivity and low oxygen content exhibited excellent photoelectric performances. In this experiment, the prepared ITO film illustrated the lowest resistivity of 1.75×10−4 Ω·cm and average transmittance of 90.5%. In sum, these findings provided a certain experimental basis for further improving the performances of ITO films.

Effects of strain on ultrahigh-performance optoelectronics and growth behavior of high-quality indium tin oxide films on yttria-stabilized zirconia (001) substrates

Effects of strain on ultrahigh-performance optoelectronics and growth behavior of high-quality indium tin oxide films on yttria-stabilized zirconia (001) substrates

Indium Tin Oxide Thin Film Deposition by Magnetron Sputtering at Room Temperature for the Manufacturing of Efficient Transparent Heaters

Indium tin oxide (ITO) thin films are widely used as transparent electrodes in electronic devices. Many of those electronic devices are heat sensitive, thus their manufacturing process steps should not exceed 100 °C. Manufacturing competitive high-quality ITO films at low temperature at industrial scale is still a challenge. Magnetron sputtering technology is the most suitable technology fulfilling those requirements. However, ITO layer properties and the reproducibility of the process are extremely sensitive to process parameters. Here, morphological, structural, electrical, and optical characterization of the ITO layers deposited at low temperature has been successfully correlated to magnetron sputtering process parameters. It has been demonstrated that the oxygen flow controls and influences layer properties. For oxygen flow between 3–4 sccm, high quality crystalline layers were obtained with excellent optoelectronic properties (resistivity &lt;8 × 10−4 Ω·cm and visible transmittance &gt;80%). The optimized conditions were applied to successfully manufacture transparent ITO heaters on large area glass and polymeric components. When a low supply voltage (8 V) was applied to transparent heaters (THs), de-icing of the surface was produced in less than 2 min, showing uniform thermal distribution. In addition, both THs (glass and polycarbonate) showed a great stability when exposed to saline solution.

Chemical and structural analysis of low-temperature excimer-laser annealing in indium-tin oxide sol-gel films

We investigated the influence of excimer-laser annealing (ELA) on the electrical, chemical, and structural properties of indium–tin oxide (ITO) films prepared by a solution process. The ITO film was prepared by the sol-gel method and annealed by excimer-laser pulses with an energy density up to 240 mJ/cm2. Hall measurements showed that the ELA substantially enhanced the electrical properties of the ITO films, including their resistivity, carrier density, and mobility, as increasing the laser energy density. In-depth x-ray photoelectron spectroscopy analysis of the chemical states in the film surface showed that the ELA reduced carbon species and promoted both an oxidation and crystallization. These changes were consistent with results of x-ray diffraction and transmission electron microscopy measurements, where expansions in the microcrystal growth were observed for higher laser energy density. We comprehensively understand that the chemical rearrangement and concomitant crystallization are the main factors for achieving the electrical properties during the ELA. These results suggest the potential of the ELA-treated sol-gel films for providing high-quality ITO films at low temperatures toward the flexible device applications.

Fabrication and Characterization of Indium Tin Oxide Films.

BackgroundTransparent conducting oxide (TCO) films are of particular interest in the field of optoelectronics, due to the requirement for transparent electrodes in applications such as organic light-emitting diodes, solar cells and so on. The aim of this study was to obtain a better understanding of the effects of preparation temperature on indium tin oxide (ITO) films, to improve their performance for optoelectronic applications.MethodsITO films were deposited on glass substrate at different temperatures, using direct current (DC) magnetron sputtering. The influence of substrate temperature on the microstructure and electrical and optical properties was studied. The surface topography and microstructure of the films were analyzed by atomic force microscopy. The electrical resistivity and optical transmittance of the films were measured using the Hall effect measurement and spectrometer, respectively.ResultsThe results showed that both the surface roughness and film thickness increased as the substrate temperature increased. Transmittance increased from 78% to 80% in the visible wavelength region, while resistivity decreased from 6.05 × 10−4 to 3.27 × 10−4 Ω-cm as the substrate temperature increased from 25°C to 275°C.ConclusionsHigh-quality ITO films with low resistivity and high transmittance can be achieved by increasing the deposition temperature.

Low-temperature and solution-processed indium tin oxide films and their applications in flexible transparent capacitive pressure sensors

It is of great interest to fabricate indium tin oxide (ITO) films by solution-based techniques at low temperatures. Here, we combined the use of colloidal ITO nanoflowers synthesized by the strategy of limited ligand protection and oxygen plasma treatment which effectively remove the surface ligands of ITO nanocrystals to meet this goal. These efforts led to high-quality ITO films with resistivity as low as 2.33 × 10−2 Ω cm, which is the best result for solution-processed ITO nanocrystal films deposited at temperatures lower than 200 °C. The annealing-free processing allowed us to deposit ITO nanoflower films onto plastic substrates and apply them in flexible capacitive pressure sensors. The single-pixel device showed decent sensitivity and reproducibility, and the arrayed sensors exhibited good spatial resolution.

Influence of Oxygen Concentration on the Performance of Ultra-Thin RF Magnetron Sputter Deposited Indium Tin Oxide Films as a Top Electrode for Photovoltaic Devices.

The opportunity for substantial efficiency enhancements of thin film hydrogenated amorphous silicon (a-Si:H) solar photovoltaic (PV) cells using plasmonic absorbers requires ultra-thin transparent conducting oxide top electrodes with low resistivity and high transmittances in the visible range of the electromagnetic spectrum. Fabricating ultra-thin indium tin oxide (ITO) films (sub-50 nm) using conventional methods has presented a number of challenges; however, a novel method involving chemical shaving of thicker (greater than 80 nm) RF sputter deposited high-quality ITO films has been demonstrated. This study investigates the effect of oxygen concentration on the etch rates of RF sputter deposited ITO films to provide a detailed understanding of the interaction of all critical experimental parameters to help create even thinner layers to allow for more finely tune plasmonic resonances. ITO films were deposited on silicon substrates with a 98-nm, thermally grown oxide using RF magnetron sputtering with oxygen concentrations of 0, 0.4 and 1.0 sccm and annealed at 300 °C air ambient. Then the films were etched using a combination of water and hydrochloric and nitric acids for 1, 3, 5 and 8 min at room temperature. In-between each etching process cycle, the films were characterized by X-ray diffraction, atomic force microscopy, Raman Spectroscopy, 4-point probe (electrical conductivity), and variable angle spectroscopic ellipsometry. All the films were polycrystalline in nature and highly oriented along the (222) reflection. Ultra-thin ITO films with record low resistivity values (as low as 5.83 × 10−4 Ω·cm) were obtained and high optical transparency is exhibited in the 300–1000 nm wavelength region for all the ITO films. The etch rate, preferred crystal lattice growth plane, d-spacing and lattice distortion were also observed to be highly dependent on the nature of growth environment for RF sputter deposited ITO films. The structural, electrical, and optical properties of the ITO films are discussed with respect to the oxygen ambient nature and etching time in detail to provide guidance for plasmonic enhanced a-Si:H solar PV cell fabrication.

Microstructural characterization of high-quality indium tin oxide films deposited by thermionically enhanced magnetron sputtering at low temperature

In this work, high-quality indium tin oxide (ITO) films are deposited by thermionically enhanced magnetron sputtering at a low deposition temperature. Microstructural evolution in the various growth stages is elucidated using material characterization techniques including grazing-incidence X-ray diffractometry and high-resolution transmission electron microscopy.Experimental results reveal that the ITO film is mainly amorphous throughout its thickness when it is deposited at ambient temperature without thermionic enhancement (TE). In contrast, the ITO film that is deposited at ambient temperature with TE has a columnar crystalline structure with grains of 40–80 nm in size. When the deposition temperature is increased to 200 °C with TE, the film exhibits a complete columnar crystalline structure throughout its thickness with grain sizes of 60–100 nm. The sputter-deposited ITO films using TE exhibit a higher average visible transmittance and a lower electrical resistivity than those without using TE because of the enhancement in their crystalline growth by the intensive ion bombardment.

Effect of surfactants on the structure and photoelectric properties of ITO films by sol-gel method

The Indium tin oxide (ITO) thin film possesses excellent photoelectric properties that enable it to act as an ideal transparent conductor. To obtain high-quality ITO films through sol-gel method, the ionic surfactant monoethanolamine and the non-ionic surfactant polyethylene glycol (PEG) were added to the ITO precursor slurry. The influences of surfactants on the structural and photoelectric properties of ITO film samples were investigated. XRD patterns indicated that surfactant monoethanolamine contributed to film predominant grain orientation along the (400) plane. The high transmittance (over 95%) was attributed to the preferred orientation and the grain size expansion of ITO films. SEM showed that the surface particle size and the morphology of ITO films were strongly dependent on the kind of surfactants used. Moving to the shortwave region, the absorption edge of the films exhibited the Burstein-Moss shift.

Enhancement in electrical and optical properties of indium tin oxide thin films grown using a pulsed laser deposition at room temperature by two-step process

The optical and electrical properties of indium tin oxide (ITO) thin films deposited using a pulsed laser deposition at room temperature can be substantially enhanced by adopting a two-step process. X-ray diffraction patterns and atomic force microscopy images were used to observe the structural properties of the films. High quality ITO films grown by two-step process could be obtained with the resistivity of 3.02 × 10 − 4 Ω cm, the carrier mobility of 32.07 cm 2/Vs, and the transparency above 90% in visible region mainly due to the enhancement of the film crystallinity and the increase of grain size.

Preparation of high quality ITO films on a plastic substrate using RF magnetron sputtering

Indium tin oxide (ITO) thin films were prepared on a plastic substrate (PMMA) by RF magnetron sputtering. A novel deposition system where the plasma deposition region and the resistive heating region are separated in space to minimize the thermal damage to the polymer substrate was utilized. The effects of intentional heating and oxygen addition on microstructure and electrical transport properties of ITO films were investigated. Conductivity of ITO films was found to be strongly dependent on their crystallinity. High conductive (sheet resistance ∼ 19 Ω/sq) and transparent (above 85%) ITO thin films (150 nm) could be obtained with a moderate heating of substrate (about 70 °C) and without introduction of oxygen gas during the deposition. It was observed that amorphous layer with thickness of ∼ 80 nm was formed at the interface on the polymer substrate and polycrystalline ITO was deposited above this thickness. Dependence of the electrical resistivity of ITO films on their thickness was also discussed.

Electrical, structural, and optical properties of ITO thin films prepared at room temperature by pulsed laser deposition

Abstract Indium tin oxide (ITO) thin films were prepared by pulsed laser deposition (PLD) on glass substrate at room temperature. Structural, optical, and electrical properties of these films were analyzed in order to investigate its dependence on oxygen pressure, and rapid thermal annealing (RTA) temperature. High quality ITO films with a low resistivity of 3.3 × 10 −4 Ω cm and a transparency above 90% were able to be formed at an oxygen pressure of 2.0 Pa and an RTA temperature of 400 °C. A four-point probe method, X-ray diffraction (XRD), atomic force microscopy (AFM), and UV–NIR grating spectrometer are used to investigate the properties of ITO films.

Effect of substrate angle on properties of ITO films deposited by cathodic arc ion plating with In–Sn alloy target

Indium tin oxide (ITO) thin films have been deposited by cathodic arc ion plating (CAIP) using In–Sn alloy target as the source material. By varying substrate angle for deposition without using any filtering technique, macroparticle free, high quality ITO films are obtained successfully. In an oxygen atmosphere of 0.5 Pa without substrate heating, the lowest resistivity and lowest absorption coefficient obtained are 2×10 −4 Ω cm and 1.6×10 −3 nm −1, respectively. Our results show that this is a simple way to reduce the macroparticles and obtain high-quality ITO films. Other properties such as film structure, surface morphology, carrier concentration and mobility have also been investigated.

A study for the bias control of indium–tin–oxide films synthesized by cesium assisted radio frequency magnetron sputtering

In order to synthesize low resistive and high transparent indium–tin–oxide (ITO) films at room temperature, cesium assisted rf plasma sputtering was performed with additional substrate bias. We tried to control positive ions by negative substrate bias and negative ions by positive substrate bias. Plasma parameters, such as plasma density and electron temperature, were also controlled by the addition of cesium. The lowest specific resistivity of 4.4×10−4 Ω cm and high preferred oriented plane of (400) spectra from x-ray diffraction were obtained at the deposition condition of −100 V substrate bias. Our method proves to be very effective in low temperature growth of high quality ITO films.

Preparation and characterization of indium tin oxide films formed by oxygen ion beam assisted deposition

Indium tin oxide (ITO) films were produced by low-energy oxygen ion beam assisted electron-beam evaporation. The dependence of surface morphology, electrical and optical properties on evaporation rate, oxygen ion beam energy and density, as well as substrate temperatures was characterized by atomic force microscopy, X-ray photoelectron spectroscopy, Hall-effect and optical transmittance measurements. The results show that high-quality ITO films (resistivity of 7.0×10 −4 Ω cm, optical transmittance above 85% at wavelength 550 nm, surface roughness of 0.6 nm in root mean square) can be obtained at room temperature.

Nitrogen as background gas in pulsed-laser deposition growth of indium tin oxide films at room temperature

The use of nitrogen as background gas to assist pulsed-laser deposition in the fabrication of indium tin oxide (ITO) films at room temperature produces both highly conductive and transparent films (∼8×10 −4 Ω cm and ∼85% of transmittance), comparable to those obtained by using oxygen (∼4×10 −4 Ω cm and ∼90% of transmittance). Hall-effect electrical measurements, Rutherford backscattering spectrometry, X-ray diffraction and optical transmission on these films are reported. For the films with best conducting and transparent properties, atomic nitrogen is 5% of the atomic oxygen content in the films. The amount of nitrogen correlates to the amount of electron-carrier concentration in the films, which suggests that incorporation of nitrogen from the background gas plays an important role in the creation of oxygen vacancies—the main conduction mechanism in high-quality ITO films grown over substrates at room temperature.