Sol Gel Indium Tin Oxide Research Articles

Enhancement of Electrical Properties of Sol-Gel Indium-Tin-Oxide Films by Microwave Irradiation and Plasma Treatment.

We proposed the enhancement of the electrical properties of solution-processed indium–tin–oxide (ITO) thin films through microwave irradiation (MWI) and argon (Ar) gas plasma treatment. A cost- and time-effective heat treatment through MWI was applied as a post-deposition annealing (PDA) process to spin-coated ITO thin films. Subsequently, the sheet resistance of MWI ITO thin films was evaluated before and after plasma treatment. The change in the sheet resistance demonstrated that MWI PDA and Ar plasma treatment significantly improved the electrical properties of the ITO thin films. Furthermore, X-ray photoelectron spectroscopy and X-ray diffraction analyses showed that the electrical properties of the ITO thin films were enhanced by the increase in oxygen vacancies due to the ion bombardment effect of high-energy plasma ions during Ar plasma treatment. Changes in the band gap structure of the ITO thin film due to the ion bombardment effect were also analyzed. The combination of MWI PDA and Ar plasma treatment presents new possibilities for improving the high-conductivity sol–gel ITO electrode.

Improvement of Structural, Electrical, and Optical Properties of Sol–Gel-Derived Indium–Tin-Oxide Films by High Efficiency Microwave Irradiation

Herein, indium-tin-oxide (ITO) thin films are prepared by a solution-based spin-coating process followed by a heat-treatment process with microwave irradiation (MWI). The structural, electrical and optical properties of the films are investigated. The properties of the microwave-irradiated sol-gel ITO films are compared with those of as-spun ITO films and sol-gel ITO films subjected to conventional furnace annealing (CFA) or a rapid thermal process (RTP). After microwave irradiation, the sol-gel ITO thin films are found to have crystallized, and they indicate enhanced conductivity and transparency. Furthermore, the resistances of the ITO films are decreased considerably at increased microwave power levels, and the resistivity of the films almost saturate even at a low microwave power of 500 W. The improved physical properties of the MW-irradiated samples are mainly due to the increase in the electron concentration of the ITO films and the increase in the carrier mobility after MWI.

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.

Fabrication and characterization of highly transparent and conductive indium tin oxide films made with different solution-based methods

Solution-based fabrication methods can greatly reduce the cost and broaden the applications of transparent conducting oxides films, such as indium tin oxide (ITO) films. In this paper, we report on ITO films fabricated by spin coating methods on glass substrates with two different ITO sources: (1) a commercial ITO nanopowder water dispersion and (2) a sol-gel ITO solution. A simple and fast air annealing process was used to treat as-coated ITO films on a controlled temperature hot plate. Thermogravimetric analysis and x-ray diffraction showed that highly crystalline ITO films were formed after the annealing steps. The final ITO films had a good combination of optical properties and electrical properties, especially for films made from five layers of sol-gel ITO (92.66% transmittance and 8.7 × 10−3 Ω cm resistivity). The surface morphology and conducting network on the ITO films were characterized by non-contact and current atomic force microscopy. It was found that conducting paths were only partially connected for the nanoparticle ITO dispersion films, whereas the sol-gel ITO films had a more uniformly distributed conducting network on the surface. We also used the sol-gel ITO films to fabricate a simple liquid crystal display (LCD) device to demonstrate the excellent properties of our films.

Sol–gel versus sputtering indium tin oxide films as transparent conducting oxide materials

The aim of this paper is the replacing of the expensive sputtering method with the low cost sol–gel one in TCO applications. To this end two sets of indium tin oxide (ITO) thin films are compared and discussed in this paper: one obtained by r.f. sputtering and one by the sol–gel technique and dip-coating. For each of these sets of samples, a series of deposition parameters have been varied in an effort to obtain the most promising optical and electrical properties. Comparative structural, morphological and opto-electrical characterization of sol–gel and sputtered ITO-based films was performed by X-ray diffraction, Scanning electron microscopy, Atomic force microscopy, Spectroellipsometry, UV–VIS Spectroscopy and Hall Effect measurements in order to establish whether the chemical deposition method could lead to thin films with competitive properties as those obtained through the physical method. Comparable, high transmittance (85–90 %) in the VIS–NIR range (250–1050 nm) and carrier concentration values (1020–1021 cm−3) were obtained between sputtered and sol–gel ITO films. The sputtered ITO film in 75 % N2, annealed at 500 °C and the sol–gel 0.1 M ITO film with 10 layers deposited on SiO2/glass exhibit degenerate semiconductor behavior.

Influence of the substrate type on the microstructural, optical and electrical properties of sol–gel ITO films

Indium tin oxide (ITO) is recognized as the best transparent and conductive material [transparent conducting oxide (TCO)] until now and its properties are dependent on the preparation method. In the present work ITO films with In:Sn atomic ratio 9:1 were prepared by a sol–gel route on different substrates (microscope glass slides, microscope glass covered with one layer of SiO2 and Si wafers) for TCO applications. The multilayer ITO films were obtained by successive deposition by the dip-coating method and the films were characterized from the structural, morphological, optical, and electrical points of view using X-ray diffraction, scanning electron microscopy, atomic force microscopy, spectroscopic ellipsometry and by Hall effect measurements, respectively. The results showed that the thickness, optical constants and carrier numbers depend strongly on the type of substrate, number of deposited layers and sol concentration. The optical properties of ITO films are closely related to their electrical properties. The enhancement of the conductivity was possible with the increase of crystallite size (which occurred after thermal treatment) and with the reduction of surface roughness.

Synthesis and characterization of smoke-like porous sol–gel indium tin oxide coatings on glass

A precursor for porous indium tin oxide (ITO) coatings with smoke-like surface feature was prepared from the hydrated metal [In(III)/Sn(IV)] salts and polyvinyl alcohol (PVA) solvated in a mixed aqueous-organic medium. Films were prepared by dip coating and cured at four temperatures (60 °C, 150 °C, 250 °C and 400 °C) where different surface features and morphological properties were obtained. The thickness of the films ranged from 0.5 to 1.2 μm. After the 60 °C cure, the surface showed a unique “smoke-like” feature of combustion products of PVA-ITO precursor. Increasing the cure temperature to 150 °C led to the development of In(III) and Sn(IV) moieties incorporated in crystalline PVA having the shape close to the hexagonal. Study of thermogravimetric analysis and differential thermal analysis of the material suggests that the gel to oxide transformation occurs by the removal of physisorbed water, PVA and nitrate ion followed by the condensation of hydroxide groups. Electrical parameters such as resistivity, conductivity, sheet resistance were evaluated by two- and four-point probe methods. Field emission scanning electron microscopy and transmission electron microscopy studies of the sample cured at 400 °C showed that the films were a porous network containing 5–40 nm clusters of ITO.

Reduced Graphite Oxide-Indium Tin Oxide Hybrid Materials for use as a Transparent Electrode

Reduced graphite oxide (rGO)-indium tin oxide (ITO) hybrid materials suitable for spin-coating transparent electrodes were synthesized and evaluated. GO was made using a modified Hummers method and was reduced by p-phenylene diamine (PPD-rGO) or hydrazine hydrate (HYD-rGO). Raman spectra showed that the G-band of PPD-rGO or HYD-rGO down-shifted from 1599 to 1583 cm−1 and the intensity ratio of the D-band with respect to the G-band increased from 0.67 to 0.91 or 0.83, indicating the recovery of the hexagonal network of carbon atoms with defects. According to elemental analysis data, oxygen content decreased from 44.34 to 19.58 and 18.30 after GO was treated by PPD or HYD. After adding 0.66 wt % PPD-rGO or HYD-rGO into sol-gel ITO, the sheet resistance of the film decreased from 2 × 103 to 1.0 × 103 or 0.7 × 103 Ω/sq, respectively. Further, transmittances as high as 87% were maintained. The operating voltage at 30 mA/cm2 in organic light emitting diodes using hybrid materials of HYD-rGO and ITO as anodes decreased from 23.8 to 14.2 V. Luminance at 90 mA/cm2 increased from 7500 to 11000 cd/m2. Therefore, rGO effectively reduces the sheet resistance of sol-gel ITO.

UV Irradiation Effect on Pattern Size Shrinkage of Sol-gel Indium Tin Oxide Replicated by Nanoimprint Lithography

The spin-coated ITO film can be delineated by room-temperature nanoimprint lithography (RT-NIL), but the patterns disappeared after 200 ?C annealing process. To overcome the above problem, we examined 254 nm UV irradiation effect onto a spin-coated ITO film. However, this result suggests that UV irradiated pattern shrink in size. In this paper, we confirmed UV irradiation effect on pattern shrinkage of sol-gel ITO replicated by RT-NIL.

UV irradiation effect on sol-gel indium tin oxide nanopatterns replicated by room-temperature nanoimprint

The authors report the first room-temperature nanoimprint lithography (RT-NIL) process using sol-gel indium tin oxide (ITO) as a replicated material. The spin-coated ITO film has to be annealed over 600°C to obtain a low resistivity. The spin-coated ITO film can be delineated by RT-NIL, but the patterns disappear after annealing at 200°C. To overcome the above problem, they examined UV irradiation effects on a spin-coated ITO film. As a result, they found that the ITO patterns imprinted by RT-NIL stayed the same after being annealed at 600°C for 1h due to 254nm UV irradiation before annealing.

Room-Temperature Nanoimprint using Sol-Gel ITO Film

We report room-temperature nanoimprint (RT-NIL) process using sol-gel indium tin oxide (ITO) as a replicated material. The spin-coated ITO film has to be annealed at over 600 °C to obtain a low resistivity. The spin-coated ITO film can be delineated by RT-NIL, but the patterns disappeared after 200 °C annealing process. To overcome the above problem, we examined the O2 plasma irradiation effect onto a spin-coated ITO film. As a result, we found that the ITO patterns imprinted by RT-NIL were kept at annealing of 600 °C for 1 hour by O2 plasma irradiation before annealing.

Synthesis of nanostructured sol–gel ITO films at different temperatures and study of their absorption and photoluminescence properties

Nanostructured indium tin oxide (ITO) films were deposited on silica glass by sol–gel dipping method from salt derived PVA based aqueous precursor. The films were cured at 250 °C, 350 °C, 450 °C, 600 °C, 700 °C and 900 °C and characterized by XRD, SEM, AFM techniques to observe heating effect on nanostructured feature. Nanocluster sizes were determined by TEM study. Different crystal phases of ITO were existed in the temperature range 250–900 °C. Quantum confinement behavior of the nanoclusters was observed for their size being near Bohr radius. Absorption, band gap and photoluminescence behavior of the nanstructured ITO films supported excitonic transitions due to the formation of electron hole pair generated by interaction of electromagnetic radiation.

Study of annealing time on sol–gel indium tin oxide films on glass

Indium and tin salt-based precursors maintaining In:Sn atomic ratio as 90:10 were utilized for the development of sol–gel dip coated indium tin oxide films (ITO) on SiO 2 coated (∼ 200 nm thickness) soda lime silica glass substrate. The gel films were initially cured in air at ∼ 450 °C to obtain oxide films of physical thickness ∼ 250 nm. These were then annealed in 95% Ar–5% H 2 atmosphere at ∼ 500 °C. The annealing time was varied from 0.5 h to 5 h. Variation of annealing time did not show any considerable change of transmittance in the visible region. Thermal emissivity ( ε d, 0.67–0.79) of the films were evaluated from their hemispherical spectral reflectance. These passed through a minima with increasing annealing time as the reflectivity of the films in the mid-IR passed through a maxima. The microstructure of the films revealed systematic growth of the ITO grains. XRD and XPS studies revealed the presence of both In and Sn metals in addition to the metal oxides. The energy dispersive X-ray (EDX) analysis showed little lowering of tin content in the films with increasing annealing time.

ITO Thin Films on Silicon Buffer by Sol Gel Method

Sol gel indium tin oxide thin films (In: Sn = 90:10) were prepared by the sol-gel dipcoating process on silicon buffer substrate. The precursor solution was prepared by mixing SnCl2.2H2O and InCl3 dissolved in ethanol and acetic acid. The crystalline structure and grain orientation of ITO films were determined by X-ray diffraction. The surface morphology of the films was characterized by scanning electron microscope (SEM). Optical transmission and reflectance spectra of the films were analyzed by using a UV-visible spectrophotometer. The transport properties of majority charge carriers for these films were studied by Hall measurement. ITO thin film with electrical resistivity of 7.6 ×10-3 3.cm, Hall mobility of approximately 2 cm2(Vs)-1 and free carrier concentration of approximately 4.2 ×1020 cm-3 are obtained for films 100 nm thick films. The I-V curve measurement showed typical I-V characteristic behavior of sol gel ITO thin films.

Work function of sol–gel indium tin oxide (ITO) films on glass

Indium tin oxide (ITO) films (physical thickness, 250–560±25nm) were deposited on soda lime silica (SLS) glass and silica layer coated (∼200nm physical thickness) SLS glass substrates by sol–gel technique using alcohol based precursors containing different In:Sn atomic percentages, namely, 90:10, 70:30, 50:50, 30:70. Cubic phase of In2O3 was observed up to 50at.% Sn while cassiterite SnO2 phase was observed for 70at.% Sn. Work function of the films was evaluated from inelastic secondary electron cutoff of ultraviolet photoelectron spectroscopy (UPS) energy distribution curve (EDC) obtained under two experimental conditions (i) as-introduced (ii) after the cleaning of the surface by sputtering. Elemental distribution and the presence of oxygen containing contaminant and carbon contaminant of the samples were done by XPS analysis under same conditions. The work function changed little due to the presence of surface contaminants. It was in the range, 3.9–4.2eV (±0.1eV).

Synthesis and photoluminescence property of nanostructured sol–gel indium tin oxide film on glass

Sol–gel dip coated indium tin oxide film of In:Sn = 90:10 was prepared on glass at 350 °C from aqueous precursor. Nanostructured feature and cubic phase of the film were characterized by scanning electron microscopy and X-ray diffraction studies, respectively. Average cluster of 4.7 nm diameter was measured by the transmission electron microscopy and it is near to Bohr radius of In 2O 3. The evaluated bandgap of the nanocluster ( E g = 4.0 eV) is consistent with the absorption band appearing for quantum confinement. The confinement phenomenon resulted in photoluminescence (PL) when excited at different photoluminescence excitation wavelengths. The PL bands have been identified as the emissions of bound and free excitons.

Study of sol–gel-derived high tin content indium tin oxide (ITO) films on silica-coated soda lime silica glass

Sol–gel indium tin oxide films (ITO) of different thickness (120±25−40 to 560±25−40 nm) and of various compositions (In:Sn=90:10, 70:30 and 50:50) prepared from In metal and Sn salt were deposited on silica-coated (∼200 nm thickness) sheet glass substrate by the spinning technique. The films were cured in reducing atmosphere (N 2+H 2O vapour) at 500±5 °C, and these were of bixbyite-type structure with cubic In 2O 3 phase. Directional hemispherical reflectance ( R h) and transmittance ( T h) of the films were measured in the wavelength range 0.25–18 μm. The R h in the IR region was found to be maximum (∼0.62 at 10 μm) for In:Sn=70:30 resulting in minimum thermal emissivity ( ε d=0.36). The thermal emissivity ( ε d) was evaluated from the relation, ε d=1− R h− T h ( T h≈0 for sheet glass in the wavelength range 5–18 μm), and it was in the range 0.36–0.85. The achieved sheet resistance of the films was in the range 55–1700 Ω/□. Resistivity of the films of relatively low sheet resistance measured by van der Pauw method at ambient temperature was in the range (1.4±0.2)×10 −3 to (3.5±0.6)×10 −3 Ω cm, and it was minimum for In:Sn=70:30 which resulted in maximum carrier concentration. Free electron carrier concentration ( N) and Hall mobility ( μ) of the films were in the range (1.4±0.4)×10 20 to (4.8±1.3)×10 20 cm −3 and (9.5±2.4) to (13±3) cm 2/V s, respectively. The Hall mobility of the films passes through minima with an increase in tin content.

Morphology, structure and optical properties of sol–gel ITO thin films

The alkoxidic route and the spinning deposition were used to prepare monolayer sol–gel indium tin oxide (ITO) films. The morphology and crystalline structure were investigated by cross-section transmission electron microscopy (XTEM) and atomic force microscopy (AFM). The ITO sol–gel mono-layer contains three regions of different porosities. The basic crystalline structure is that of the In 2O 3 lattice. The optical properties have been studied by optical transmission and spectroscopic ellipsometry.

Effects of tin on IR reflectivity, thermal emissivity, Hall mobility and plasma wavelength of sol–gel indium tin oxide films on glass

Sol–gel indium tin oxide films (ITO) of various composition (In:Sn atomic ratio=90:10 to 30:70) prepared from salt-based precursors were deposited on bare and SiO2 coated (∼200 nm thickness) sheet glass substrates. The films were cured in air and then annealed under N2/H2O at ∼500 °C to obtain ITO films of thickness 250–320 nm. Directional hemispherical reflectance (Rh) and trasmittance (Th) of the films were measured in the wavelength range 0.25–18 μm. The reflectance of the films at 10 μm (near the peak wavelength of black body radiation) was in the range 0.18–0.55. The thermal emissivity (εd) was evaluated from the relation: εd=1−Rh−Th (Th≈0, for sheet glass in the wavelength range 5–18 μm) and it was in the range 0.47–0.90. Reflectance (Rh) was also evaluated from measured sheet resistance values (R□), from the relation Rh=(1+2ε0c0R□)−2, where ε0 and c0 are the permittivity of electron in vacuum and velocity of light, respectively. Specific resistivity of the films, measured by van-der Pauw method at ambient temperature was in the range 1.7±0.3×10−3 to 6.6±1.2×10−3 Ω cm. The sheet resistance (R□) of the films was in the range 68–212 Ω/□. Free electron carrier concentration (N) and Hall mobility (μ) of the films were in the ranges (0.66±0.18)×1020 to (3.7±1.0)×1020 cm−3 and (4.4±1.5) to (20±5) cm2/V s, respectively. These values were utilized to evaluate plasma wavelength (λP) of the conducting films which were in the range 1.72±0.24–4.07±0.58 μm. Considerable variations of the above properties were observed with increasing Sn content but minimum thermal emissivity and maximum IR reflectivity were observed in the case of In:Sn=70:30.