Properties of indium tin oxide films prepared by ion-assisted deposition

Conducting transparent films of indium tin oxide were deposited by 100 eV oxygen-ion-assisted deposition. A refractive index of 2.13 at 550 nm was obtained for films deposited onto ambient temperature substrates. The refractive index decreased with increasing substrate temperature to a value of 2.0 at 400°C. The sheet resistance of films 135 nm thick decreased from 800 Ω/□ for layers deposited onto room temperature substrates to around 25 Ω/□ at 400°C. Structural studies revealed that ion-assisted deposition onto ambient temperature substrates produced amorphous films, and that at temperatures above 100°C the films exhibit In₂O₃ crystallinity. In addition, it was found that the number of voids in the ion-bombarded films was reduced relative to that in films produced by conventional reactive evaporation.     

Low temperature deposition of tin oxide films by inductively coupled plasma assisted chemical vapor deposition

Well-crystallized tin oxide films were successfully synthesized without additional heating by inductively coupled plasma assisted chemical vapor deposition (ICP-CVD). The degree of crystallization was affected by the ICP power and hydrogen flow rate. The substrate temperature was increased only up to 423-453 K by plasma heating, which suggests that the formation of the SnO₂ crystals was not caused by plasma heating, but by enhanced reactivity of precursors in high density plasma. The micro-hardness of deposited tin oxide films ranged from 5.5 to 11 GPa at different hydrogen flow rates.     

Pulsed laser deposition of conductive indium tin oxide thin films

Thin indium tin oxide (ITO) films have been grown on quartz glass substrates by pulsed laser deposition. The influence of ablation target composition and deposition conditions on the growth rate, optical transmission spectra, and carrier mobility and concentration of the films has been examined. The average surface roughness of the ITO films grown at substrate temperatures above 300°C is 2 nm. The films grown at an oxygen partial pressure of 5 mTorr using ablation targets with Sn/(In + Sn) = 5% possess high transmission (85-95%) in the visible range and low resistivity (1.8 × 10⁻⁴ Ω cm).     

Transparent and heat-reflecting indium tin oxide films prepared by reactive electron beam evaporation

Transparent and heat-reflecting indium tin oxide films were prepared by electron beam evaporation of In₂O₃9mol.%SnO₂ in an oxygen atmosphere of about 5×10^?4 Torr. A visible absorption of less than 2%, a thermal IR reflectance exceeding 90% and a d.c. resistivity of approximately 3×10^?4 Ω cm were obtained from films 0.4 μm thick deposited at a substrate temperature of 300°C. Films with similar properties could be prepared with substrate temperatures as low as 150°C.     

Low temperature remote plasma sputtering of indium tin oxide for flexible display applications

Tin doped indium oxide (ITO) has been directly deposited onto a variety of flexible materials by a reactive sputtering technique that utilises a remotely generated, high density plasma. This technique, known as high target utilisation sputtering (HiTUS), allows for the high rate deposition of good quality ITO films onto polymeric materials with no substrate heating or post deposition annealing. Coatings with a resistivity of 3.8 × 10^− 4 Ωcm and an average visible transmission of greater than 90% have been deposited onto PEN and PET substrate materials at a deposition rate of 70 nm/min. The electrical and optical properties are retained when the coatings are flexed through a 1.0 cm bend radius, making them of interest for flexible display applications.     

Tungsten-doped tin oxide thin films prepared by pulsed plasma deposition

Transparent conductive oxide tungsten-doped tin oxide thin films were deposited on glass substrates from ceramic targets by the pulsed plasma deposition method. The structural, electrical and optical properties have been investigated as functions of tungsten doping content and oxygen partial pressure. The lowest resistivity of 2.1 × 10^? 3 Ω?cm was reproducibly obtained, with carrier mobility of 30 cm²V^? 1s^? 1 and carrier concentration of 9.6 × 10¹⁹ cm^? 3 at the oxygen partial pressure of 1.8 Pa. The average optical transmission was in excess of 80% in the visible region from 400 to 700 nm, with the optical band gap ranging from 3.91 to 4.02 eV.     

Surface treatments of indium tin oxide films by using high density plasma

We investigated the effects of various surface treatments on the work function and chemical composition of an indium tin oxide (ITO) surface. Ultraviolet photoelectron spectroscopy (UPS) was used to measure the work function of ITO. X-ray photoelectron spectroscopy (XPS) was used to study the electron structures of ITO surface. We performed surface treatments on ITO using O₂ plasma and HCl solution. Our UPS/XPS analysis indicates increases in the work functions by O₂ plasma treatments. It is known that the Fermi energy level is controlled by the donor concentration, and thus the Fermi energy level is shifted toward the valence band minimum.     

Pulsed laser deposition of indium tin oxide films on flexible polyethylene naphthalate display substrates at room temperature

Pulsed laser deposition was used to deposit high-quality indium tin oxide (ITO) thin solid films on polyethylene napthalate (PEN) flexible display substrates. The electrical, optical, microstructural, mechanical and adhesive properties of the functional thin layer were investigated as a function of a narrow range of background oxygen gas pressure at room temperature, which is the most desirable thermal condition for growing transparent conducting oxides on flexible display polymer substrates. ITO films (240 ± 35 nm thick) deposited on PEN at room temperature in the range of 0.33 to 2.66 Pa background oxygen pressure are observed to exhibit low electrical resistivity (~ 10^− 4 Ω cm) and high optical transmission (~ 90%). Electromechanical uniaxial tensile testing, of the hybrid thin structures, results in crack onset nominal strains of around 2%. The ITO surface adhesion reaches a maximum at 1.33 Pa deposition pressure.     

Properties of indium oxide films prepared by the reactive evaporation of indium

Indium oxide films with an electrical resistivity of about $\text{4 × 10}{}^{\mathrm{?4}}\text{Ω}\text{cm}$ and good optical quality were prepared by the reactive evaporation of pure indium in the presence of 10^?4 Torr of oxygen. The Auger electron spectrum of these films shows a deficiency of oxygen and corresponds to a composition which can be represented as In₂O_2.85. In the absence of foreign doping agents, the conduction electrons are provided by indium atoms which are adjacent to oxygen vacancies and act as a donor level. The electrical conductivity of the films is shown to be modulated by variations in the partial pressure of oxygen over the film which change the extent of the non-stoichiometry of the oxide by incorporation of oxygen into or extraction of oxygen from the film.     

Characterization of nanocrystalline indium tin oxide thin films prepared by ion beam sputter deposition method

Indium tin oxide (ITO) thin films were deposited on glass substrates by ion beam sputter deposition method in three different deposition conditions [(i) oxygen (O₂) flow rate varied from 0.05 to 0.20 sccm at a fixed argon (1.65 sccm) flow rate, (ii) Ar flow rate changed from 1.00 to 1.65 sccm at a fixed O₂ (0.05 sccm) flow rate, and (iii) the variable parameter was the deposition time at fixed Ar (1.65 sccm) and O₂ (0.05 sccm) flow rates]. (i) The X-ray diffraction (XRD) patterns show that the ITO films have a preferred orientation along (400) plane; the orientation of ITO film changes from (400) to (222) direction as the O₂ flow rate is increased from 0.05 to 0.20 sccm. The optical transmittance in the visible region increases with increasing O₂ flow rate. The sheet resistance (R_s) of ITO films also increases with increasing O₂ flow rate; it is attributed to the decrease of oxygen vacancies in the ITO film. (ii) The XRD patterns show that the ITO film has a strong preferred orientation along (222) direction. The optical transmittance in the visible spectral region increases with an increase in Ar flow rate. The R_s of ITO films increases with increasing Ar flow rate; it is attributed to the decrease of grain size in the films. (iii) A change in the preferred orientations of ITO films from (400) to (222) was observed with increasing film thickness from 314 to 661 nm. The optical transmittance in the visible spectral region increases after annealing at 200 °C. The R_s of ITO film decreases with the increase of film thickness.     

Properties of indium tin oxide films deposited on unheated polymer substrates by ion beam assisted deposition

The optical, electrical and mechanical properties of indium tin oxide (ITO) films prepared on polyethylene terephthalate (PET) substrates by ion beam assisted deposition at room temperature were investigated. The properties of ITO films can be improved by introducing a buffer layer of silicon dioxide (SiO₂) between the ITO film and the PET substrate. ITO films deposited on SiO₂-coated PET have better crystallinity, lower electrical resistivity, and improved resistance stability under bending than those deposited on bare PET. The average transmittance and the resistivity of ITO films deposited on SiO₂-coated PET are 85% and 0.90 × 10^− 3 Ω cm, respectively, and when the films are bent, the resistance remains almost constant until a bending radius of 1 cm and it increases slowly under a given bending radius with an increase of the bending cycles. The improved resistance stability of ITO films deposited on SiO₂-coated PET is mainly attributed to the perfect adhesion of ITO films induced by the SiO₂ buffer layer.     

Etching methods for indium oxide/tin oxide films

Methods are described for etching patterns in conducting indium-tin oxide films on glass substrates. For patterns requiring maximum definition and resolution hydriodic acid is preferred, whereas hydrofluoric acid or zinc and hydrochloric acid are useful for other purposes.     

Annealing effects in indium oxide films prepared by reactive evaporation

The annealing effects of reactively evaporated indium oxide films in various ambients at temperatures of up to approximately 350°C are reported. It is concluded that the changes in the electrical parameters of the films are due to the chemisorption or desorption of oxygen atoms from the grain boundaries. From these studies the grain boundary barrier heights are found to be 26 meV and 43 meV for as-deposited and air-annealed films respectively.     

Eu-doped indium tin oxide thin films fabricated by sol-gel technique

We have fabricated Eu-doped indium tin oxide thin films via the conventional sol-gel technique, and confirmed that the doped Eu atoms were chemically incorporated into the indium tin oxide lattice by substituting the In sites. Optical spectra indicated that the Eu-doped films were free of any impurities leading to additional vibrational effects. Valence states of Eu ions in our Eu-doped indium tin oxide films were discussed in connection with Eu concentration.     

Deposition of indium tin oxide by atmospheric pressure chemical vapour deposition

We report the deposition of indium tin oxide (ITO) by atmospheric pressure chemical vapour deposition (APCVD). This process is potentially scalable for high throughput, large area production. We utilised a previously unreported precursor combination; dimethylindium acetylacetonate, [Me₂In(acac)] and monobutyltintrichloride, MBTC.[Me₂In(acac)] is a volatile solid. It is more stable and easier to handle than traditional indium oxide precursors such as pyrophoric trialkylindium compounds. Monobutyltintrichloride (MBTC) is also easily handled and can be readily vaporised. It is compatible with the process conditions required for using [Me₂In(acac)].Cubic ITO was deposited at a substrate temperature of 550 °C with growth rates exceeding 15 nm/s and growth efficiencies of between 20 and 30%. Resistivity was 3.5 × 10^− 4 Ω cm and transmission for a 200 nm film was > 85% with less than 2% haze.     

Variations in microstructure and composition of indium tin oxide films with the deposition technique

Indium tin oxide (ITO) films have been deposited by reactive d.c.-sputtering and also by the reactive thermal evaporation technique onto glass substrates. The relationship between the microstructure and composition of the ITO films was found to strongly depend on the deposition technique. In addition the application of pure water vapour as the reactive sputtering atmosphere and its influence on the structural and compositional properties of the ITO films has been studied.X-ray diffraction investigations showed that all the films exhibited the bixbite structure of In₂O₃. No other crystalline phases were observed. Highly crystallized ITO films have been obtained using the reactive thermal evaporation technique. These films show a large average grain size of about 80 nm and a very homogeneous morphology. In contrast the d.c.-sputtered ITO films have a smaller average grain size and a characteristic texture. All deposited ITO films show an enlarged lattice constant compared to that of In₂O₃. A strong dependence of the chemical composition of the ITO films on the deposition technique and parameters was detected.     

Ultraflat indium tin oxide films prepared by ion beam sputtering

Indium tin oxide (ITO) films with a smooth surface (root-mean-square roughness; R_rms=0.40 nm) were made using a combination of the deposition conditions in the ion beam-sputtering method. Sheet resistance was 13.8 Ω/sq for a 150-nm-thick film grown at 150 °C. Oxygen was fed into the growth chamber during film growth up to 15 nm, after which, the oxygen was turned off throughout the rest of the deposition. The surface of the films became smooth with the addition of ambient oxygen but electrical resistance increased. In films grown at 150 °C with no oxygen present, a rough surface (R_rms=2.1 nm) and low sheet resistance (14.4 Ω/sq) were observed. A flat surface (R_rms=0.5 nm) with high sheet resistance (41 Ω/sq) was obtained in the films grown with ambient oxygen throughout the film growth. Surface morphology and microstructure of the films were determined by the deposition conditions at the beginning of the growth. Therefore, fabrication of ITO films with a smooth surface and high electrical conductivity was possible by combining experimental conditions.     

Preparation of transparent conductive indium tin oxide thin films from nanocrystalline indium tin hydroxide by dip-coating method

Indium tin oxide (ITO) thin films with well-controlled layer thickness were produced by dip-coating method. The ITO was synthesized by a sol-gel technique involving the use of aqueous InCl₃, SnCl₄ and NH₃ solutions. To obtain stable sols for thin film preparation, as-prepared Sn-doped indium hydroxide was dialyzed, aged, and dispersed in ethanol. Polyvinylpyrrolidone (PVP) was applied to enhance the stability of the resulting ethanolic sols. The transparent, conductive ITO films on glass substrates were characterized by X-ray diffraction, scanning electron microscopy and UV-Vis spectroscopy. The ITO layer thickness increased linearly during the dipping cycles, which permits excellent controllability of the film thickness in the range ~ 40-1160 nm. After calcination at 550 °C, the initial indium tin hydroxide films were transformed completely to nanocrystalline ITO with cubic and rhombohedral structure. The effects of PVP on the optical, morphological and electrical properties of ITO are discussed.