Sputtered Indium Tin Oxide Films Research Articles

Control of preferred (222) crystalline orientation of sputtered indium tin oxide thin films

We report a two-step growth process for the fabrication of (222)-plane textured indium tin oxide (ITO) films. A thin ITO seed layer was grown in mixed Argon+Oxygen gases, followed by a thick ITO deposited in Argon gas. X-Ray diffraction shows that the sputtered ITO films exhibit strongly preferred (222) crystalline orientation. The (222)-plane textured ITO films have high transmittance above 80% in the visible range and carrier concentration, mobility and resistivity in the range of 1021cm−3, 40cm2/Vs and 10−4Ω·cm, respectively. The surface roughness of our (222) textured ITO films is 1.4nm, which is one of the smallest value obtained from sputtered ITO thin films.

Optical analysis of room temperature magnetron sputtered ITO films by reflectometry and spectroscopic ellipsometry

Abstract

Investigation into inhomogeneous electrical and optical properties of indium tin oxide film using spectroscopic ellipsometry with multi-layer optical models

Indium tin oxide (ITO) films with various thicknesses are deposited on glass substrates using a DC magnetron sputtering technique. The microstructure and chemical composition of the sputtered samples are examined by scanning electron microscopy (SEM), X-Ray Diffraction (XRD) and Energy Dispersive X-Ray Spectroscopy (EDS). Two-layer and three-layer optical models of the sputtered ITO films are constructed for fitting the experimental results of the spectroscopic ellipsometry. The results obtained from the two models for the resistivity, carrier density and carrier mobility are compared with those obtained via Hall effect measurements. Finally, the three-layer optical model is used to evaluate the refractive index and extinction coefficient spectra of the various samples. In general, the present results show that the three-layer model, in which the transition layer between the ITO film and the glass substrate is included, provides a better approximation of the SE results than the two-layer model. However, both models yield a reasonable estimate of the Hall resistivity. The results obtained using the three-layer model show that the carrier density and carrier mobility in the bulk layer are lower and higher, respectively, than those in the transition layer. In addition, it is shown that the refractive index of the bulk layer is lower than that of the transition layer in the UV and visible spectrum. Moreover, the extinction coefficient of the transition layer is significantly higher than that of the bulk layer in the near IR-region.

Effects of Post Annealing Temperatures on Sputtered Indium Tin Oxide Films for the Application to Resistive Touch Panel

Indium tin oxide (ITO) films were deposited on glass substrates by in-line DC sputtering and were annealed at different temperatures in the main chamber of sputter. The post-annealing effects on the optical and electrical properties of the ITO films were investigated and analyzed by various measurement systems. The results show that a higher annealing temperature makes an improvement on the electro-optical properties of the ITO films. The resistivity of the ITO films was reduced from 8.90×10−4Ω·cm to 2.91×10−4Ω·cm and the transmittance was increased from about 76.91% to 82.15% after post annealing at 300 °C in vacuum. The post annealed ITO glass was used in the fabrication of resistive touch panel and it was possible to obtain the better linearity characteristics than those from the touch panel fabricated with non-annealed ITO glass.

Gravure Printing of ITO Transparent Electrodes for Applications in Flexible Electronics

The possibility to directly pattern indium-tin-oxide (ITO) layers at ambient conditions by printing has many benefits. Printing, being an additive process, would greatly reduce the amount of energy, labor and material used by the current manufacturing processes to deposit and pattern ITO. In this work, gravure printability of ITO nanoparticles on polyethylene terephthalate (PET) was studied. A wide range of sheet resistivites and film thicknesses was obtained by varying the specifications of the gravure cells. From the regression analysis of the results, a good estimation of sheet resistivity of the printed films at different gravure cell volumes and aspect ratios (AR) was achieved. The films also showed transparency above 95% in the visible light region. In addition, printed ITO films were assessed for mechanical flexibility and the results compared to commercially available sputtered ITO films on PET. The electrical performance of printed ITO layers was not deteriorated with bending in contrast to the sputtered films. Therefore, printed ITO films can be of great benefit for applications in flexible electronics such as organic photovoltaics (OPV), liquid crystal displays (LCD), organic light-emitting diodes (OLED), touch screens, biosensors and utilization in the field of energy efficiency, especially in buildings.

Selectively transparent and conducting photonic crystal solar spectrum splitters made of alternating sputtered indium-tin oxide and spin-coated silica nanoparticle layers for enhanced photovoltaics

Selectively-transparent and conducting photonic crystals (STCPCs) made of alternating layers of sputtered indium-tin oxide (ITO) and spin-coated silica (SiO2) nanoparticle films exhibit Bragg-reflectance peaks in the visible spectrum of 95% reflectivity and have a full width at half maximum that is greater than 200nm. At the same time, their conductive properties are comparable to that of solid sputtered ITO films. Moreover, the average transmission of the STCPCs in the pass-band can be increased to ∼88%, or within 3.3% of the bare glass slide they are fabricated on. Furthermore, we also show that these STCPCs can readily be fabricated on textured surfaces similar to those used for micromorph solar cells. In this context wave optics analysis shows that these STCPCs can be utilized as intermediate reflectors that boost the relative photo-current generated in textured micromorph cells by more than 20% over a broad range of incident angles.

Structural, electrical and optical properties of indium tin oxide thin films prepared by RF sputtering using different density ceramic targets

There is an active demand for the commercial indium tin oxide (ITO) target with density above 99% of the theoretical density (TD). Some works found the increase of the target density could lead to a slight decrease of the resistivity of the direct current (DC) sputtered ITO films, however, the possible effect of target density on the radio frequency (RF) sputtered ITO films is not clear. In this paper, ITO targets with different densities are successfully prepared. The structural, electrical and optical properties of the thin films deposited from these targets are studied at the substrate temperature of 750 °C. It is found that the target density has no effect on the above properties and the deposition rate of the RF sputtered ITO thin films, different from the DC sputtered films. So for the RF sputtered process, the target needs not high density so that the used target can be just compacted from the powders without sintering. All the as-prepared ITO films with different densities have a resistivity of 1.56 × 10−4 Ω cm and a transmittance of ∼87%, which are lower than the ITO films prepared at temperatures lower than 400 °C.

Elemental distribution and oxygen deficiency of magnetron sputtered indium tin oxide films

The atomic structure and composition of noninterfacial ITO and ITO-Si interfaces were studied with transmission electron microscopy and x-ray photoelectron spectroscopy (XPS). The films were deposited by dc magnetron sputtering on monocrystalline p-type (100) Si wafers. Both as deposited and heat treated films consisted of crystalline ITO. The ITO/Si interface showed a more complicated composition. A thin layer of SiOx was found at the ITO/Si interface together with In and Sn nanoclusters, as well as highly oxygen deficient regions, as observed by XPS. High energy electron exposure of this area crystallized the In nanoclusters and at the same time increased the SiOx interface layer thickness.

Structural, optical, and electrical properties of E-beam and sputter-deposited ITO films for LED applications

The structural, electrical, and optical properties of e-beam and sputter-deposited Indium-Tin-Oxide (ITO) films on sapphire and p-GaN wafers, as well as the post-deposition annealing effect for light-emitting-diode applications, were analyzed and compared. The specific contact resistance of the sputtered ITO film on a p-GaN wafer was found to be slightly higher than that of the e-beam deposited ITO films. However, in general, the electrical, structural and optical properties of the sputtered ITO films that were annealed at comparably lower temperature are better than those of the e-beam deposited ITO films, which is the consequence of a larger average grain size. The sputtered ITO film that was annealed at 500°C demonstrated a resistivity of as low as 3.6 × 10−4 Ω·cm, along with a high transmittance of ∼98% at 450 nm.

Influence of film thickness on the texture, morphology and electro-optical properties of indium tin oxide films

Abstract In the present study, the structural, electrical, and optical properties of indium tin oxide (ITO) films are reported as a function of film thickness (162–840 nm). The properties are discussed in terms of the (100) preferred orientation evolution with the increase of film thickness. This preferred orientation allowed accommodation of more oxygen vacancies, resulting in the increase of carrier concentration from 2.43 × 10 20 cm −3 to 7.11 × 10 20 cm −3 and therefore enhancing the electrical conductivity. The absorption in the infrared region was also found to increase with the increasing free carrier concentration, which was attributed to the plasma excitation. The X-ray photoelectron spectroscopy depth profile showed that the Sn 4+ concentration did not change with film thickness. However, the oxygen concentration was decreased slightly after the thickness of the ITO films was increased to 100 nm, as the consequence of the formation of the (100) texture allowing the accommodation of more oxygen vacancies. The results show that the fabrication process can be manipulated to control the electrical properties and the infrared absorption of the sputtered ITO films.

Development of low temperature RF magnetron sputtered ITO films on flexible substrate

Indium tin oxide (ITO) is one of the important materials used as transparent conducting oxide (TCO) layer in thin film solar cells, digital displays and other similar applications. For applications involving flexible polymeric substrates, it is important that deposition of ITO is carried out at near room temperature. This requirement puts constraint on stoichiometry leading to undesired electrical and optical properties. Effect of oxygen partial pressure on ITO films deposited on flexible Kapton ® by the RF magnetron sputtering is reported in this paper.

HRBS/channeling studies of ultra-thin ITO films on Si

High-resolution Rutherford backscattering spectroscopy (HRBS)/channeling techniques have been utilized for a detailed characterization of ultra-thin indium tin oxide (ITO) films and to probe the nature of the interface between the ITO film and the Si(001) substrate. Channeling studies provide a direct measure of the lattice strain distribution in the crystalline Si substrate in the case of amorphous over layers. The measurements on DC magnetron sputtered ITO films have been carried out using the recently installed HRBS facility at the Centre for Ion Beam Applications (CIBA). The thickness of the ultra-thin (∼9.8nm) ITO films was calculated from the HRBS spectra having an energy resolution of about 1.4keV at the superimposed leading (In+Sn) edge of the ITO film. The films were near stoichiometric and the interface between ITO film and Si was found to include a thin SiOx transition layer. The backscattering yields from (In+Sn) of ITO were equal in random and channeling directions, thereby revealing the non-crystalline nature of the film. Angular scans of HRBS spectra around the off-normal [111] axis clearly showed a shift in the channeling minimum indicative of compressive strain of the Si lattice at the SiOx/Si interface. The observed strain was about 0.8% near the interface and decreased to values below our detection limits at a depth of ∼3nm from the SiOx/Si interface.

Room temperature crystallization of indium tin oxide films on glass and polyethylene terephthalate substrates using rf plasma

The crystallization of amorphous indium tin oxide (ITO) films was achieved by rf (13.56MHz) plasma treatment. Although the films were crystallized after 2min, the sample temperature was lower than 90°C without compulsory cooling even after 10min of treatment and polyethylene terephthalate (PET) substrates had no damage. Plasma-crystallized sputtered ITO films have a bixbite structure and the resistivity reached to 1.6×10−4Ω∙cm. ITO thin films have almost the same resistivity in both cases of PET and glass substrates used and plasma-treated PET ITO films have a bit higher resistivity than that of glass ITO films, while mass spectroscopy measurements indicated that ITO films deposited on PET substrates are expected to include no apparent gas species ejected from PET substrate. It was found that the plasma gas pressure is the key parameter for the effective crystallization and the appropriate gas pressure depends on the plasma gas species.

Structural, optical and electrical peculiarities of r.f. plasma sputtered indium tin oxide films

In this work the influence of the deposition conditions on the structural, electrical and optical properties of the ITO films was studied. Films were deposited by r.f. plasma sputtering technique in Ar and varying Ar + O 2 gas mixtures, with and without substrate heating. Transmittance and reflectance of the films were measured in the range 350–2500 nm; the refractive index ( n) and the extinction coefficient ( k) were calculated by the spectral data simulation. The sheet resistance of the films was measured by four-point probe method. X-ray diffraction analysis was performed to study the texture of the films. Threshold behaviour was observed in the optical and electrical properties of ITO films deposited in Ar + O 2 atmosphere at a certain oxygen concentration determined by a fix combination of all other deposition conditions. A schematic diagram for the change of the film properties versus composition was suggested, which explains the obtained results.

Preparation and properties of RF sputtered indium–tin oxide thin films for applications as heat mirrors in photothermal solar energy conversion

In the present research, in order to deposit indium–tin oxide (ITO) thin films the method of RF reactive sputtering was used. Sputtering of two types indium–tin targets in the presence of oxygen as reactive gas was made. The technological parameters were optimized to obtain films with good quality on different substrates. The films' microstructure was studied by TEM and SAED. To identify the optical properties of the films the methods of infrared spectrometry and laser ellipsometry were used. UV–VIS spectrophotometry showed the high visible transmittance of the RF sputtered ITO films. Heating of the substrates during the films sputtering and their post deposition thermal treatment also were studied. The ultimate goal of the present research activities was to develop new technological processes leading to low-cost, highly effective optical coatings for application in photo thermal solar energy conversion and utilization.

Effects of post-thermal treatment on the properties of rf reactive sputtered ITO films

Indium tin oxide (ITO) thin film prepared by rf sputtering at various Ar–O2 mixtures, were annealed at several temperatures. The electrical, optical and structural properties of the film were systematically investigated before and after post-thermal treatment. The influence of a reactive gas (O2) on the sputtering rate of a metallic (indium/tin) alloy target was also investigated. The films were characterized by X-ray diffraction (XRD) measurement, scanning electron microscopy, and transmittance as a function of wavelength. The resistivity of 8.3×10−4Ωcm has been achieved for the film thickness of 250nm, deposited in pure Ar at room temperature (RT).

Substrate Dependence of Properties of Sputtered ITO Films

High-quality indium-tin-oxide (ITO) films are deposited on p-typeCzochralski silicon and 7059 Corning glass by direct-current magnetronsputtering at various temperatures. The structural, electrical andoptical properties of the ITO films are investigated as functions ofthe substrate temperature. A comparison between the characteristics ofthe ITO films on silicon and Corning glass is presented. The resultsshow that for the ITO film on silicon, the nucleation begins from roomtemperature; the resistivity reaches a maximum value at 75°C;the reflectivity increases with increasing temperature; whentemperature is above 125°C, the ITO grows in athree-dimensional manner and forms a granular structure. However, forthe ITO film on glass, it is still in an amorphous state at75°C. Moreover, both the resistivity and the reflectivitydecrease with increasing temperature. Above 125°C, the ITOgrows in a two-dimensional manner and forms a domain structure.

GaN Photodetectors with Transparent Indium Tin Oxide Electrodes

Sputtering indium tin oxide (ITO) and e-beam ITO films deposited onto GaN as transparent electrodes for applications in metal–semiconductor–metal (MSM) photodetectors were fabricated and reported. The transmittances of 1000 Å-thick sputtering-ITO and e-beam ITO films were 78% and 67%, respectively, at a wavelength of 350 nm. The variation in the transmittance of the sputtering ITO films was not dependent on film thickness. The estimated effective barrier heights of the sputtering ITO and e-beam ITO films to GaN were 0.46 and 0.95 eV, respectively. This difference in barrier height originates from the formation of InGaN at the interface of ITO/GaN. Finally, GaN MSM photodetectors were fabricated using e-beam ITO electrodes. The peak responsivity of these e-beam ITO MSM photodetectors was 0.11 A/W at a 3 V bias. For a given bandwidth of 500 Hz, the corresponding noise equivalent power (NEP) and normalized detectivity D* were calculated to be 1.51×10-10 W and 2.96×109 cmHz0.5W-1, respectively.

Electro-structural and Film Growth Properties of Room-temperature Deposited Indium-Tin-Oxide on Polymer Substrates

ABSTRACTElectrical and structural properties of indium-tin-oxide (ITO) films on flexible polymer substrates were investigated. Room temperature sputtered ITO films on polymer substrates are initially amorphous but become partially crystalline as oxygen partial pressure decreases under 1.5%. The crystallinity shows more (400) and (222) preferentially oriented textures as decreasing of oxygen pressure resulting in lower resistivity. Moreover, an interesting growth property similar to 3D growth mechanism including larger grain size and columnar-like grain structure was also observed. It is considered that the columnar-like grain structure is probably attributed to the poor surface morphology of polymer substrates Based on the experiments, we obtained high performance ITO films on a polycarbonate substrate including 3.8 × 10 –4 Ω-cm in resistivity and transmittance above 80% in the visible ranges at 0.2% oxygen partial pressure.

Deposition of indium–tin-oxide films on polymer substrates for application in plastic-based flat panel displays

Indium–tin-oxide (ITO) films (1000±100 Å) were deposited on glass and polymer (polyethersulfone) substrates by RF-magnetron sputtering for plastic-based flat-panel displays. A novel device and a stepped heating process were used both to eliminate the tensile force and to diminish the thermal expansion of the polymer substrates. Therefore, we succeeded in sputtering ITO films without any cracking or shrinkage of the polymer substrates. The oxygen partial pressure and post-deposition annealing conditions were varied to observe the dependence of the optical, electrical and etching properties of ITO films on the process parameters. The substrate material was polyethersulfone with a gas barrier layer. Moreover, in order to investigate the influences of the process parameters, X-ray diffractometer observations and measurement of transmission, sheet resistance and residual resistance after etching process were performed. We found that oxygen content in the polymer matrix resulted from the gas absorption of polymer substrates cause different dependence of polymer substrates on oxygen partial pressure compare with glass substrates. Consequently, we could obtain high conductive ( 20–25 Ω □ −1) and transparent (above 80%) ITO films deposited on polymer substrates using the condition of 0.2% oxygen partial pressure and vacuum annealing at the temperature of 180°C.